Recent Global Warming As Depicted by AIRS, GISSTEMP, and MERRA-2

NASA Astrophysics Data System (ADS)

Susskind, J.; Iredell, L. F.; Lee, J. N.

2017-12-01

We observed anomalously warm global mean surface temperatures since 2015. The year 2016 represents the warmest annual mean surface skin and surface air temperatures in the AIRS observational period, September 2002 through August 2017. Additionally, AIRS monthly mean surface skin temperature, from January 2016 through September 2016, and November 2016, were the warmest observed for each month of the year. Continuing this trend, the AIRS global surface temperatures of 2017 February and April show the second greatest positive anomalies from average. This recent warming is particularly significant over the Arctic where the snow and sea ice melt is closely tied to the spring and summer surface temperatures. In this paper, we show the global distribution of surface temperature anomalies as observed by AIRS over the period September 2002 through August 2017 and compare them with those from the GISSTEMP and MERRA-2 surface temperatures. The spatial patterns of warm and cold anomalies for a given month show reasonably good agreement in all three data set. AIRS anomalies, which do not have the benefit of in-situ measurements, are in almost perfect agreement with those of MERRA-2, which does use in-situ surface measurements. GISSTEMP anomaly patterns for the most part look similar to those of AIRS and MERRA-2, but are more spread out spatially, and consequently are also weaker.

The biogeophysical effects of extreme afforestation in modeling future climate

NASA Astrophysics Data System (ADS)

Wang, Ye; Yan, Xiaodong; Wang, Zhaomin

2014-11-01

Afforestation has been deployed as a mitigation strategy for global warming due to its substantial carbon sequestration, which is partly counterbalanced with its biogeophysical effects through modifying the fluxes of energy, water, and momentum at the land surface. To assess the potential biophysical effects of afforestation, a set of extreme experiments in an Earth system model of intermediate complexity, the McGill Paleoclimate Model-2 (MPM-2), is designed. Model results show that latitudinal afforestation not only has a local warming effect but also induces global and remote warming over regions beyond the forcing originating areas. Precipitation increases in the northern hemisphere and decreases in southern hemisphere in response to afforestation. The local surface warming over the forcing originating areas in northern hemisphere is driven by decreases in surface albedo and increases in precipitation. The remote surface warming in southern hemisphere is induced by decreases in surface albedo and precipitation. The results suggest that the potential impact of afforestation on regional and global climate depended critically on the location of the forest expansion. That is, afforestation in 0°-15°N leaves a relatively minor impact on global and regional temperature; afforestation in 45°-60°N results in a significant global warming, while afforestation in 30°-45°N results in a prominent regional warming. In addition, the afforestation leads to a decrease in annual mean meridional oceanic heat transport with a maximum decrease in forest expansion of 30°-45°N. These results can help to compare afforestation effects and find areas where afforestation mitigates climate change most effectively combined with its carbon drawdown effects.

Was early Mars warmed by ammonia?

NASA Technical Reports Server (NTRS)

Kasting, J. F.; Brown, L. L.; Acord, J. M.; Pollack, J. B.

1992-01-01

Runoff channels and valley networks present on ancient, heavily cratered Martian terrain suggests that the climate of Mars was originally warm and wet. One explanation for the formation of these channels is that the surface was warmed by the greenhouse effect of a dense, CO2 atmosphere. However, recent work shows that this theory is not consistent for the early period of the solar system. One way to increase the surface temperature predicted is to assume that other greenhouse gases were present in Mars' atmosphere in addition to CO2 and H2O. This possible gas is ammonia, NH3. If ammonia was present in sufficient quantities, it could have raised the surface temperature to 273 K. An adequate source would have been volcanic outgassing if the NH3 produced was shielded from photolysis by an ultraviolet light absorber.

Role of Stratospheric Water Vapor in Global Warming from GCM Simulations Constrained by MLS Observation

NASA Astrophysics Data System (ADS)

Wang, Y.; Stek, P. C.; Su, H.; Jiang, J. H.; Livesey, N. J.; Santee, M. L.

2014-12-01

Over the past century, global average surface temperature has warmed by about 0.16°C/decade, largely due to anthropogenic increases in well-mixed greenhouse gases. However, the trend in global surface temperatures has been nearly flat since 2000, raising a question regarding the exploration of the drivers of climate change. Water vapor is a strong greenhouse gas in the atmosphere. Previous studies suggested that the sudden decrease of stratospheric water vapor (SWV) around 2000 may have contributed to the stall of global warming. Since 2004, the SWV observed by Microwave Limb Sounder (MLS) on Aura satellite has shown a slow recovery. The role of recent SWV variations in global warming has not been quantified. We employ a coupled atmosphere-ocean climate model, the NCAR CESM, to address this issue. It is found that the CESM underestimates the stratospheric water vapor by about 1 ppmv due to limited representations of the stratospheric dynamic and chemical processes important for water vapor variabilities. By nudging the modeled SWV to the MLS observation, we find that increasing SWV by 1 ppmv produces a robust surface warming about 0.2°C in global-mean when the model reaches equilibrium. Conversely, the sudden drop of SWV from 2000 to 2004 would cause a surface cooling about -0.08°C in global-mean. On the other hand, imposing the observed linear trend of SWV based on the 10-year observation of MLS in the CESM yields a rather slow surface warming, about 0.04°C/decade. Our model experiments suggest that SWV contributes positively to the global surface temperature variation, although it may not be the dominant factor that drives the recent global warming hiatus. Additional sensitivity experiments show that the impact of SWV on surface climate is mostly governed by the SWV amount at 100 hPa in the tropics. Furthermore, the atmospheric model simulations driven by observed sea surface temperature (SST) show that the inter-annual variation of SWV follows that of SST, suggesting a close coupling between surface temperature and SWV.

Dependence of Arctic climate on the latitudinal position of stationary waves and to high-latitudes surface warming

NASA Astrophysics Data System (ADS)

Shin, Yechul; Kang, Sarah M.; Watanabe, Masahiro

2017-12-01

Previous studies suggest large uncertainties in the stationary wave response under global warming. Here, we investigate how the Arctic climate responds to changes in the latitudinal position of stationary waves, and to high-latitudes surface warming that mimics the effect of Arctic sea ice loss under global warming. To generate stationary waves in an atmospheric model coupled to slab ocean, a series of experiments is performed where the thermal forcing with a zonal wavenumber-2 (with zero zonal-mean) is prescribed at the surface at different latitude bands in the Northern Hemisphere. When the stationary waves are generated in the subtropics, the cooling response dominates over the warming response in the lower troposphere due to cloud radiative effects. Then, the low-level baroclinicity is reduced in the subtropics, which gives rise to a poleward shift of the eddy driven jet, thereby inducing substantial cooling in the northern high latitudes. As the stationary waves are progressively generated at higher latitudes, the zonal-mean climate state gradually becomes more similar to the integration with no stationary waves. These differences in the mean climate affect the Arctic climate response to high-latitudes surface warming. Additional surface heating over the Arctic is imposed to the reference climates in which the stationary waves are located at different latitude bands. When the stationary waves are positioned at lower latitudes, the eddy driven jet is located at higher latitude, closer to the prescribed Arctic heating. As baroclinicity is more effectively perturbed, the jet shifts more equatorward that accompanies a larger reduction in the poleward eddy transport of heat and momentum. A stronger eddy-induced descending motion creates greater warming over the Arctic. Our study calls for a more accurate simulation of the present-day stationary wave pattern to enhance the predictability of the Arctic warming response in a changing climate.

Climate Response to Negative Greenhouse Gas Radiative Forcing in Polar Winter

NASA Astrophysics Data System (ADS)

Flanner, M. G.; Huang, X.; Chen, X.; Krinner, G.

2018-02-01

Greenhouse gas (GHG) additions to Earth's atmosphere initially reduce global outgoing longwave radiation, thereby warming the planet. In select environments with temperature inversions, however, increased GHG concentrations can actually increase local outgoing longwave radiation. Negative top of atmosphere and effective radiative forcing (ERF) from this situation give the impression that local surface temperatures could cool in response to GHG increases. Here we consider an extreme scenario in which GHG concentrations are increased only within the warmest layers of winter near-surface inversions of the Arctic and Antarctic. We find, using a fully coupled Earth system model, that the underlying surface warms despite the GHG addition exerting negative ERF and cooling the troposphere in the vicinity of the GHG increase. This unique radiative forcing and thermal response is facilitated by the high stability of the polar winter atmosphere, which inhibit thermal mixing and amplify the impact of surface radiative forcing on surface temperature. These findings also suggest that strategies to exploit negative ERF via injections of short-lived GHGs into inversion layers would likely be unsuccessful in cooling the planetary surface.

The Question of Future Droughts in a CO2-Warmed World

NASA Technical Reports Server (NTRS)

Rind, David

1999-01-01

Increased droughts are to be expected in a warmer world, and so are increased floods. A warmer atmosphere can hold more moisture, and evaporate more water from the surface. Thus, when it is not raining, available soil water should be reduced. When it is raining, it could very well rain harder. Most researchers agree then that a warmer world will have greater hydrologic extremes. In addition, there is a basic imbalance that develops as climate warms, between the loss of moisture from the soil by evaporation and replenishment via precipitation. The land has a smaller heat capacity than the ocean, so it should warm faster. Evaporation from the land proceeds at the rate of its warming, while precipitation derives primarily from evaporation at the ocean surface. As the latter is increasing more slowly, in a warmer world, precipitation will not increase as rapidly as evaporation due to the fact that the oceans warm more slowly than the land surface (evaporation over the ocean is slower than over the land). Hence, more droughts are anticipated in a warmer world, but the specific location of such droughts is somewhat uncertain. To address the question of where droughts are likely to occur, one first needs to have a reasonable sense of what the future magnitude of warming will be, and what the latitudinal distribution of warming will be. For example, the greater the warming at high latitudes relative to low latitudes, the more likely there will be increased drought over the U.S. in summer. In contrast, substantial tropical warming could give us El Nino-like precipitation, with intensified flooding along the southern tier of the U.S. All of these conditions are likely to intensify as the global temperature rises.

Aerosol reductions could dominate regional climate responses in low GHG emission scenarios

NASA Astrophysics Data System (ADS)

Samset, B. H.; Sand, M.; Smith, C. J.; Bauer, S.; Forster, P.; Fuglestvedt, J. S.; Osprey, S. M.; Schleussner, C. F.

2017-12-01

Limiting global warming to current political goals requires strong, rapid mitigation of anthropogenic greenhouse gas (GHG) emissions. Concurrently, emissions of anthropogenic aerosols will decline sharply, due to co-emission with greenhouse gases, and future measures to improve air quality. As the net climate effect of GHG and aerosol emissions over the industrial era is poorly constrained, predicting the impact of strong aerosol emission reductions remains challenging. Here we investigate the isolated and compound climate impacts from removing present day anthropogenic emissions of black carbon (BC), organic carbon (OC) and SO2, and moderate, near term GHG dominated global warming, using four coupled climate models. As the dominating effect of aerosol emission reduction is a removal of cooling from sulphur, the resulting climate impacts amplify those of GHG induced warming. BC emissions contribute little to reducing surface warming, but have stronger regional impacts. For the major aerosol emission regions, extreme weather indices are more sensitive to aerosol removal than to GHG increases, per degree of surface warming. East Asia in particular stands out, mainly due to the high present regional aerosol emissions. We show how present climate models indicate that future regional climate change will depend strongly on changes in loading and distribution of aerosols in the atmosphere, in addition to surface temperature change.

Surface clay formation during short-term warmer and wetter conditions on a largely cold ancient Mars

NASA Astrophysics Data System (ADS)

Bishop, Janice L.; Fairén, Alberto G.; Michalski, Joseph R.; Gago-Duport, Luis; Baker, Leslie L.; Velbel, Michael A.; Gross, Christoph; Rampe, Elizabeth B.

2018-03-01

The ancient rock record for Mars has long been at odds with climate modelling. The presence of valley networks, dendritic channels and deltas on ancient terrains points towards running water and fluvial erosion on early Mars1, but climate modelling indicates that long-term warm conditions were not sustainable2. Widespread phyllosilicates and other aqueous minerals on the Martian surface3-6 provide additional evidence that an early wet Martian climate resulted in surface weathering. Some of these phyllosilicates formed in subsurface crustal environments5, with no association with the Martian climate, while other phyllosilicate-rich outcrops exhibit layered morphologies and broad stratigraphies7 consistent with surface formation. Here, we develop a new geochemical model for early Mars to explain the formation of these clay-bearing rocks in warm and wet surface locations. We propose that sporadic, short-term warm and wet environments during a generally cold early Mars enabled phyllosilicate formation without requiring long-term warm and wet conditions. We conclude that Mg-rich clay-bearing rocks with lateral variations in mixed Fe/Mg smectite, chlorite, talc, serpentine and zeolite occurrences formed in subsurface hydrothermal environments, whereas dioctahedral (Al/Fe3+-rich) smectite and widespread vertical horizonation of Fe/Mg smectites, clay assemblages and sulphates formed in variable aqueous environments on the surface of Mars. Our model for aluminosilicate formation on Mars is consistent with the observed geological features, diversity of aqueous mineralogies in ancient surface rocks and state-of-the-art palaeoclimate scenarios.

Amplification of global warming through pH dependence of DMS production simulated with a fully coupled Earth system model

NASA Astrophysics Data System (ADS)

Schwinger, Jörg; Tjiputra, Jerry; Goris, Nadine; Six, Katharina D.; Kirkevåg, Alf; Seland, Øyvind; Heinze, Christoph; Ilyina, Tatiana

2017-08-01

We estimate the additional transient surface warming ΔTs caused by a potential reduction of marine dimethyl sulfide (DMS) production due to ocean acidification under the high-emission scenario RCP8.5 until the year 2200. Since we use a fully coupled Earth system model, our results include a range of feedbacks, such as the response of marine DMS production to the additional changes in temperature and sea ice cover. Our results are broadly consistent with the findings of a previous study that employed an offline model set-up. Assuming a medium (strong) sensitivity of DMS production to pH, we find an additional transient global warming of 0.30 K (0.47 K) towards the end of the 22nd century when DMS emissions are reduced by 7.3 Tg S yr-1 or 31 % (11.5 Tg S yr-1 or 48 %). The main mechanism behind the additional warming is a reduction of cloud albedo, but a change in shortwave radiative fluxes under clear-sky conditions due to reduced sulfate aerosol load also contributes significantly. We find an approximately linear relationship between reduction of DMS emissions and changes in top of the atmosphere radiative fluxes as well as changes in surface temperature for the range of DMS emissions considered here. For example, global average Ts changes by -0. 041 K per 1 Tg S yr-1 change in sea-air DMS fluxes. The additional warming in our model has a pronounced asymmetry between northern and southern high latitudes. It is largest over the Antarctic continent, where the additional temperature increase of 0.56 K (0.89 K) is almost twice the global average. We find that feedbacks are small on the global scale due to opposing regional contributions. The most pronounced feedback is found for the Southern Ocean, where we estimate that the additional climate change enhances sea-air DMS fluxes by about 9 % (15 %), which counteracts the reduction due to ocean acidification.

An investigation of the effects from a urethral warming system on temperature distributions during cryoablation treatment of the prostate: a phantom study.

PubMed

Favazza, C P; Gorny, K R; King, D M; Rossman, P J; Felmlee, J P; Woodrum, D A; Mynderse, L A

2014-08-01

Introduction of urethral warmers to aid cryosurgery in the prostate has significantly reduced the incidence of urethral sloughing; however, the incidence rate still remains as high as 15%. Furthermore, urethral warmers have been associated with an increase of cancer recurrence rates. Here, we report results from our phantom-based investigation to determine the impact of a urethral warmer on temperature distributions around cryoneedles during cryosurgery. Cryoablation treatments were simulated in a tissue mimicking phantom containing a urethral warming catheter. Four different configurations of cryoneedles relative to urethral warming catheter were investigated. For each configuration, the freeze-thaw cycles were repeated with and without the urethral warming system activated. Temperature histories were recorded at various pre-arranged positions relative to the cryoneedles and urethral warming catheter. In all configurations, the urethral warming system was effective at maintaining sub-lethal temperatures at the simulated surface of the urethra. The warmer action, however, was additionally demonstrated to potentially negatively impact treatment lethality in the target zone by elevating minimal temperatures to sub-lethal levels. In all needle configurations, rates of freezing and thawing were not significantly affected by the use of the urethral warmer. The results indicate that the urethral warming system can protect urethral tissue during cryoablation therapy with cryoneedles placed as close as 5mm to the surface of the urethra. Using a urethral warming system and placing multiple cryoneedles within 1cm of each other delivers lethal cooling at least 5mm from the urethral surface while sparing urethral tissue. Copyright © 2014 Elsevier Inc. All rights reserved.

Causes of the large warm bias in the Angola-Benguela Frontal Zone in the Norwegian Earth System Model

NASA Astrophysics Data System (ADS)

Koseki, Shunya; Keenlyside, Noel; Demissie, Teferi; Toniazzo, Thomas; Counillon, Francois; Bethke, Ingo; Ilicak, Mehmet; Shen, Mao-Lin

2018-06-01

We have investigated the causes of the sea surface temperature (SST) bias in the Angola-Benguela Frontal Zone (ABFZ) of the southeastern Atlantic Ocean simulated by the Norwegian Earth System Model (NorESM). Similar to other coupled-models, NorESM has a warm SST bias in the ABFZ of up to 8 °C in the annual mean. Our analysis of NorESM reveals that a cyclonic surface wind bias over the ABFZ drives a locally excessively strong southward (0.05 m/s (relative to observation)) Angola Current displacing the ABFZ southward. A series of uncoupled stand-alone atmosphere and ocean model simulations are performed to investigate the cause of the coupled model bias. The stand-alone atmosphere model driven with observed SST exhibits a similar cyclonic surface circulation bias; while the stand-alone ocean model forced with the reanalysis data produces a warm SST in the ABFZ with a magnitude approximately half of that in the coupled NorESM simulation. An additional uncoupled sensitivity experiment shows that the atmospheric model's local negative surface wind curl generates anomalously strong Angola Current at the ocean surface. Consequently, this contributes to the warm SST bias in the ABFZ by 2 °C (compared to the reanalysis forced simulation). There is no evidence that local air-sea feedbacks among wind stress curl, SST, and sea level pressure (SLP) affect the ABFZ SST bias. Turbulent surface heat flux differences between coupled and uncoupled experiments explain the remaining 2 °C warm SST bias in NorESM. Ocean circulation, upwelling and turbulent heat flux errors all modulate the intensity and the seasonality of the ABFZ errors.

Recent global-warming hiatus tied to equatorial Pacific surface cooling.

PubMed

Kosaka, Yu; Xie, Shang-Ping

2013-09-19

Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century, challenging the prevailing view that anthropogenic forcing causes climate warming. Various mechanisms have been proposed for this hiatus in global warming, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970-2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Niña-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase.

Effect of the greenhouse gases (CO2, H2O, SO2) on Martian paleoclimate

NASA Technical Reports Server (NTRS)

Postawko, S. E.; Kuhn, W. R.

1986-01-01

There is general agreement that certain surface features on Mars are indicative of the presence of liquid water at various times in the geologic past. In particular, the valley networks are difficult to explain by a mechanism other than the flow of liquid water. It has been suggested in several studies that a thick CO2 atmosphere on Mars early in its history could have provided a greenhouse warming that would have allowed the flow of water either on the surface or just below the surface. However, this effect was examined with a detailed radiation model, and it was found that if reduced solar luminosity early in the history of the solar system is taken into account, even three bars of CO2 will not provide sufficient greeenhouse warming. The addition of water vapor and sulflur dioxide (both plausible gases that may have been emitted by Martian volcanoes) to the atmosphere also fail to warm the surface above 273 K for reduced solar luminosity conditions. The increase in temperature may be large enough, however, for the formation of these features by brines.

Arctic Sea Ice Basal Melt Onset Variability and Associated Ocean Surface Heating

NASA Astrophysics Data System (ADS)

Merrick, R. A.; Hutchings, J. K.

2015-12-01

The interannual and regional variability in Arctic sea ice melt has previously been characterized only in terms of surface melting. A focus on the variability in the onset of basal melt is additionally required to understand Arctic melt patterns. Monitoring basal melt provides a glimpse into the importance of ocean heating to sea ice melt. This warming is predominantly through seawater exposure due to lead opening and the associated solar warming at the ocean's surface. We present the temporal variability in basal melt onset observed by ice mass balance buoys throughout the Arctic Ocean since 2003, providing a different perspective than the satellite microwave data used to measure the onset of surface melt. We found that melt onset varies greatly, even for buoys deployed within 100km of each other. Therefore large volumes of data are necessary to accurately estimate the variability of basal melt onset. Once the variability of basal melt onset has been identified, we can investigate how this range has been changing as a response to atmospheric and oceanic warming, changes in ice morphology as well as the intensification of the ice albedo feedback.

The Impact of Transported Pollution on Arctic Climate

NASA Astrophysics Data System (ADS)

Quinn, P.; Stohl, A.; Arneth, A.; Berntsen, T.; Burkhart, J. F.; Flanner, M. G.; Kupiainen, K.; Shepherd, M.; Shevchenko, V. P.; Skov, H.; Vestreng, V.

2011-12-01

Arctic temperatures have increased at almost twice the global average rate over the past 100 years. Warming in the Arctic has been accompanied by an earlier onset of spring melt, a lengthening of the melt season, changes in the mass balance of the Greenland ice sheet, and a decrease in sea ice extent. Short-lived, climate warming pollutants such as black carbon (BC) have recently gained attention as a target for immediate mitigation of Arctic warming in addition to reductions in long lived greenhouse gases. Model calculations indicate that BC increases surface temperatures within the Arctic primarily through deposition on snow and ice surfaces with a resulting decrease in surface albedo and increase in absorbed solar radiation. In 2009, the Arctic Monitoring and Assessment Program (AMAP) established an Expert Group on BC with the goal of identifying source regions and energy sectors that have the largest impact on Arctic climate. Here we present the results of this work and investigate links between mid-latitude pollutants and Arctic climate.

Northwestern Pacific typhoon intensity controlled by changes in ocean temperatures.

PubMed

Mei, Wei; Xie, Shang-Ping; Primeau, François; McWilliams, James C; Pasquero, Claudia

2015-05-01

Dominant climatic factors controlling the lifetime peak intensity of typhoons are determined from six decades of Pacific typhoon data. We find that upper ocean temperatures in the low-latitude northwestern Pacific (LLNWP) and sea surface temperatures in the central equatorial Pacific control the seasonal average lifetime peak intensity by setting the rate and duration of typhoon intensification, respectively. An anomalously strong LLNWP upper ocean warming has favored increased intensification rates and led to unprecedentedly high average typhoon intensity during the recent global warming hiatus period, despite a reduction in intensification duration tied to the central equatorial Pacific surface cooling. Continued LLNWP upper ocean warming as predicted under a moderate [that is, Representative Concentration Pathway (RCP) 4.5] climate change scenario is expected to further increase the average typhoon intensity by an additional 14% by 2100.

Effects of turbulence on warm clouds and precipitation with various aerosol concentrations

NASA Astrophysics Data System (ADS)

Lee, Hyunho; Baik, Jong-Jin; Han, Ji-Young

2015-02-01

This study investigates the effects of turbulence-induced collision enhancement (TICE) on warm clouds and precipitation by changing the cloud condensation nuclei (CCN) number concentration using a two-dimensional dynamic model with bin microphysics. TICE is determined according to the Taylor microscale Reynolds number and the turbulent dissipation rate. The thermodynamic sounding used in this study is characterized by a warm and humid atmosphere with a capping inversion layer, which is suitable for simulating warm clouds. For all CCN concentrations, TICE slightly reduces the liquid water path during the early stage of cloud development and accelerates the onset of surface precipitation. However, changes in the rainwater path and in the amount of surface precipitation that are caused by TICE depend on the CCN concentrations. For high CCN concentrations, the mean cloud drop number concentration (CDNC) decreases and the mean effective radius increases due to TICE. These changes cause an increase in the amount of surface precipitation. However, for low CCN concentrations, changes in the mean CDNC and in the mean effective radius induced by TICE are small and the amount of surface precipitation decreases slightly due to TICE. A decrease in condensation due to the accelerated coalescence between droplets explains the surface precipitation decrease. In addition, an increase in the CCN concentration can lead to an increase in the amount of surface precipitation, and the relationship between the CCN concentration and the amount of surface precipitation is affected by TICE. It is shown that these results depend on the atmospheric relative humidity.

Evaluation of Foaming Performance of Bitumen Modified with the Addition of Surface Active Agent

NASA Astrophysics Data System (ADS)

Chomicz-Kowalska, Anna; Mrugała, Justyna; Maciejewski, Krzysztof

2017-10-01

The article presents the analysis of the performance of foamed bitumen modified using surface active agents. Although, bitumen foaming permits production of asphalt concrete and other asphalt mix types without using chemical additives in significantly reduced temperatures, the decrease in processing temperatures still impacts the adhesion performance and bitumen coating of aggregates in final mixes. Therefore, in some cases it may be feasible to incorporate adhesion promoters and surface active agents into warm and half-warm mixes with foamed bitumen to increase their service life and resilience. Because of the various nature of the available surface active agents, varying bitumen compatibility and their possible impact on the rheological properties of bitumen, the introduction of surface active agents may significantly alter the bitumen foaming performance. The tests included basic performance tests of bitumen before and after foaming. The two tested bitumen were designated as 35/50 and 50/70 penetration grade binders, which were modified with a surface active agent widely used for improving mixture workability, compactibility and adhesion in a wide range of asphalt mixes and techniques, specifically Warm Mix Asphalt. Alongside to the reference unmodified bitumen, binders with 0.2%, 0.4% and 0.6% surface active agent concentration were tested. The analysis has shown a positive influence of the modifier on the foaming performance of both of the base bitumen increasing their maximum expansion ratio and bitumen foam halflife. In the investigations, it was found that the improvement was dependent on the bitumen type and modifier content. The improved expansion ratio and foam half-life has a positive impact on the aggregate coating and adhesion, which together with the adhesion promoting action of the modifier will have a combined positive effect on the quality of produced final asphalt mixes.

The 2014-2015 warming anomaly in the Southern California Current System observed by underwater gliders

NASA Astrophysics Data System (ADS)

Zaba, Katherine D.; Rudnick, Daniel L.

2016-02-01

Large-scale patterns of positive temperature anomalies persisted throughout the surface waters of the North Pacific Ocean during 2014-2015. In the Southern California Current System, measurements by our sustained network of underwater gliders reveal the coastal effects of the recent warming. Regional upper ocean temperature anomalies were greatest since the initiation of the glider network in 2006. Additional observed physical anomalies included a depressed thermocline, high stratification, and freshening; induced biological consequences included changes in the vertical distribution of chlorophyll fluorescence. Contemporaneous surface heat flux and wind strength perturbations suggest that local anomalous atmospheric forcing caused the unusual oceanic conditions.

Mechanism for Surface Warming in the Equatorial Pacific during 1994-95

NASA Technical Reports Server (NTRS)

Rienecker, Michele M.; Borovikov, Anna; Schopf, Paul S.

1999-01-01

Mechanisms controlling the variation in sea surface temperature warm event in the equatorial Pacific were investigated through ocean model simulations. In addition, the mechanisms of the climatological SST cycle were investigated. The dominant mechanisms governing the seasonal cycle of SST vary significantly across the basin. In the western Pacific the annual cycle of SST is primarily in response to external heat flux. In the central basin the magnitude of zonal advection is comparable to that of the external heat flux. In the eastern basin the role of zonal advection is reduced and the vertical mixing is more important. In the easternmost equatorial Pacific the vertical entrainment contribution is as large as that of vertical diffusion. The model estimate of the vertical mixing contribution to the mixed layer heat budget compared well with estimates obtained by analysis of observations using the same diagnostic vertical mixing scheme. During 1994- 1995 the largest positive SST anomaly was observed in the mid-basin and was related to reduced latent heat flux due to weak surface winds. In the western basin the initial warming was related to enhanced external heating and reduced cooling effects of both vertical mixing and horizontal advection associated with weaker than usual wind stress. In the eastern Pacific where winds were not significantly anomalous throughout 1994-1995, only a moderate warm surface anomaly was detected. This is in contrast to strong El Nino events where the SST anomaly is largest in the eastern basin and, as shown by previous studies, the anomaly is due to zonal advection rather than anomalous surface heat flux. The end of the warm event was marked by cooling in July 1995 everywhere across the equatorial Pacific.

Atmospheric transport, clouds and the Arctic longwave radiation paradox

NASA Astrophysics Data System (ADS)

Sedlar, Joseph

2016-04-01

Clouds interact with radiation, causing variations in the amount of electromagnetic energy reaching the Earth's surface, or escaping the climate system to space. While globally clouds lead to an overall cooling radiative effect at the surface, over the Arctic, where annual cloud fractions are high, the surface cloud radiative effect generally results in a warming. The additional energy input from absorption and re-emission of longwave radiation by the clouds to the surface can have a profound effect on the sea ice state. Anomalous atmospheric transport of heat and moisture into the Arctic, promoting cloud formation and enhancing surface longwave radiation anomalies, has been identified as an important mechanism in preconditioning Arctic sea ice for melt. Longwave radiation is emitted equally in all directions, and changes in the atmospheric infrared emission temperature and emissivity associated with advection of heat and moisture over the Arctic should correspondingly lead to an anomalous signal in longwave radiation at the top of the atmosphere (TOA). To examine the role of atmospheric heat and moisture transport into the Arctic on TOA longwave radiation, infrared satellite sounder observations from AIRS during 2003-2014 are analyzed for summer (JJAS). Thermodynamic metrics are developed to identify months characterized by a high frequency of warm and moist advection into the Arctic, and segregate the 2003-14 time period into climatological and anomalously warm, moist summer months. We find that anomalously warm, moist months result in a significant TOA longwave radiative cooling, which is opposite the forcing signal that the surface experiences during these months. At the timescale of the advective events, 3-10 days, the TOA cooling can be as large as the net surface energy budget during summer. When averaged on the monthly time scale, and over the full Arctic basin (poleward of 75°N), summer months experiencing frequent warm, moist advection events are observed with a TOA longwave flux to space that is 2 to 4 W m-2 larger than climatology. This represents a significant climate cooling signal, suggestive of a regional climate buffering mechanism to combat excessive Arctic warming.

Temperature Data Shows Warming in 2001

NASA Technical Reports Server (NTRS)

2002-01-01

TThe figure above depicts how much air temperatures near the Earth's surface changed relative to the global mean temperature from 1951 to 1980. NASA researchers used maps of urban areas derived from city lights data to account for the 'heat island' effect of cities. The red and orange colors show that temperatures are warmer in most regions of the world when compared to the 1951 to 1980 'normal' temperatures. Warming around the world has been widespread, but it is not present everywhere. The largest warming is in Northern Canada, Alaska and Siberia, as indicated by the deeper red colors. The lower 48 United States have become warmer recently, but only enough to make the temperatures comparable to what they were in the 1930s. The scale on the bottom of these temperature anomaly images represent degrees in Celsius. The negative numbers represent cooling and the positive numbers depict warming. Overall, the air temperature near the Earth's surface has warmed by 1oF (0.6oC) globally, on average, over the last century. For more information and additional images, read Satellites Shed Light on a Warmer World. Image courtesy Goddard Institute for Space Studies (GISS).

Relative roles of differential SST warming, uniform SST warming and land surface warming in determining the Walker circulation changes under global warming

NASA Astrophysics Data System (ADS)

Zhang, Lei; Li, Tim

2017-02-01

Most of CMIP5 models projected a weakened Walker circulation in tropical Pacific, but what causes such change is still an open question. By conducting idealized numerical simulations separating the effects of the spatially uniform sea surface temperature (SST) warming, extra land surface warming and differential SST warming, we demonstrate that the weakening of the Walker circulation is attributed to the western North Pacific (WNP) monsoon and South America land effects. The effect of the uniform SST warming is through so-called "richest-get-richer" mechanism. In response to a uniform surface warming, the WNP monsoon is enhanced by competing moisture with other large-scale convective branches. The strengthened WNP monsoon further induces surface westerlies in the equatorial western-central Pacific, weakening the Walker circulation. The increase of the greenhouse gases leads to a larger land surface warming than ocean surface. As a result, a greater thermal contrast occurs between American Continent and equatorial Pacific. The so-induced zonal pressure gradient anomaly forces low-level westerly anomalies over the equatorial eastern Pacific and weakens the Walker circulation. The differential SST warming also plays a role in driving low-level westerly anomalies over tropical Pacific. But such an effect involves a positive air-sea feedback that amplifies the weakening of both east-west SST gradient and Pacific trade winds.

Development of an Urban Multilayer Radiation Scheme and Its Application to the Urban Surface Warming Potential

NASA Astrophysics Data System (ADS)

Aoyagi, Toshinori; Takahashi, Shunji

2012-02-01

To investigate how a three-dimensional structure such as an urban canyon can affect urban surface warming, we developed an urban multilayer radiation scheme. The complete consideration of multiple scattering of shortwave and longwave radiation using the radiosity method is an important feature of the present scheme. A brief description of this scheme is presented, followed by evaluations that compare its results with observations of the effective albedo and radiative temperature for urban blocks. Next, we calculate the urban surface warming potential (USWP), defined as the difference between the daily mean radiative temperature of urban surfaces (which are assumed to be black bodies), including their canyon effects and the daily mean temperature of a flat surface with the same material properties, under a radiative equilibrium state. Assuming standard material properties (albedo and emissivity of 0.4 and 0.9, respectively), we studied the sensitivity of the USWP to various aspect ratios of building heights to road widths. The results show that the temporally-averaged surface temperature of an urban area can be higher than that of a flat surface. In addition, we determined the overestimation of the effective temperature of urban surfaces induced by the overestimation of the radiation distribution to the walls when one uses a single-layer scheme for urban block arrays that have a low sky-view factor less than around 0.5.

Multiple climate regimes in an idealized lake-ice-atmosphere model

NASA Astrophysics Data System (ADS)

Sugiyama, Noriyuki; Kravtsov, Sergey; Roebber, Paul

2018-01-01

In recent decades, the Laurentian Great Lakes have undergone rapid surface warming with the summertime trends substantially exceeding the warming rates of surrounding land. Warming of the deepest (Lake Superior) was the strongest, and that of the shallowest (Lake Erie)—the weakest of all lakes. To investigate the dynamics of accelerated lake warming, we considered single-column and multi-column thermodynamic lake-ice models coupled to an idealized two-layer atmosphere. The variable temperature of the upper atmospheric layer—a proxy for the large-scale atmospheric forcing—consisted, in the most general case, of a linear trend mimicking the global warming and atmospheric interannual variability, both on top of the prescribed seasonal cycle of the upper-air temperature. The atmospheric boundary layer of the coupled model exchanged heat with the lake and exhibited lateral diffusive heat transports between the adjacent atmospheric columns. In simpler single-column models, we find that, for a certain range of periodic atmospheric forcing, each lake possesses two stable equilibrium seasonal cycles, which we call "regimes"—with and without lake-ice occurrence in winter and with corresponding cold and warm temperatures in the following summer, respectively, all under an identical seasonally varying external forcing. Deeper lakes exhibit larger differences in their summertime surface water temperature between the warm and cold regimes, due to their larger thermal and dynamical inertia. The regime behavior of multi-column coupled models is similar but more complex, and in some cases, they admit more than two stable equilibrium seasonal cycles, with varying degrees of wintertime ice-cover. The simulated lake response to climate change in the presence of the atmospheric noise rationalizes the observed accelerated warming of the lakes, the correlation between wintertime ice cover and next summer's lake-surface temperature, as well as higher warming trends of the (occasionally wintertime ice-covered) deep-lake vs. shallow-lake regions, in terms of the corresponding characteristics of the forced transitions between colder and warmer lake regimes. Since the regime behavior in our models arises due to nonlinear dynamics rooted in the ice-albedo feedback, this feedback is also the root cause of the accelerated lake warming simulated by these models. In addition, our results imply that if Lake Superior eventually becomes largely ice-free (<10% maximum ice cover every winter) under continuing global warming, the surface warming trends of the deeper regions of the lake will become modest, similar to those of the shallower regions of the lake.

Interhemispheric SST gradient trends in the Indian Ocean prior to and during the recent global warming hiatus

NASA Astrophysics Data System (ADS)

Dong, L.; McPhaden, M. J.

2016-12-01

Sea surface temperatures (SSTs) have been rising for decades in the Indian Ocean in response to greenhouse gas forcing. However, in this study we show that during the recent hiatus in global warming, a striking interhemispheric gradient in Indian Ocean SST trends developed around 2000, with relatively weak or little warming to the north of 10°S and accelerated warming to the south of 10oS. We present evidence from a wide variety of data sources that this interhemispheric gradient in SST trends is forced primarily by an increase of Indonesian Throughflow (ITF) transport from the Pacific into the Indian Ocean induced by stronger Pacific trade winds. This increased transport led to a depression of the thermocline that facilitated SST warming presumably through a reduction in the vertical turbulent transport of heat in the southern Indian Ocean. Surface wind changes in the Indian Ocean linked to the enhanced Walker circulation also may have contributed to thermocline depth variations and associated SST changes, with downwelling favorable wind stress curls between 10oS and 20oS and upwelling favorable wind stress curls between the equator and 10oS. In addition, the anomalous southwesterly wind stresses off the coast of Somalia favored intensified coastal upwelling and off-shore advection of upwelled water, which would have led to reduced warming of the northern Indian Ocean. Though highly uncertain, lateral heat advection associated with the ITF and surface heat fluxes may also have played a role in forming the interhemispheric SST gradient change.

Shifting grassland plant community structure drives positive interactive effects of warming and diversity on aboveground net primary productivity.

PubMed

Cowles, Jane M; Wragg, Peter D; Wright, Alexandra J; Powers, Jennifer S; Tilman, David

2016-02-01

Ecosystems worldwide are increasingly impacted by multiple drivers of environmental change, including climate warming and loss of biodiversity. We show, using a long-term factorial experiment, that plant diversity loss alters the effects of warming on productivity. Aboveground primary productivity was increased by both high plant diversity and warming, and, in concert, warming (≈1.5 °C average above and belowground warming over the growing season) and diversity caused a greater than additive increase in aboveground productivity. The aboveground warming effects increased over time, particularly at higher levels of diversity, perhaps because of warming-induced increases in legume and C4 bunch grass abundances, and facilitative feedbacks of these species on productivity. Moreover, higher plant diversity was associated with the amelioration of warming-induced environmental conditions. This led to cooler temperatures, decreased vapor pressure deficit, and increased surface soil moisture in higher diversity communities. Root biomass (0-30 cm) was likewise consistently greater at higher plant diversity and was greater with warming in monocultures and at intermediate diversity, but at high diversity warming had no detectable effect. This may be because warming increased the abundance of legumes, which have lower root : shoot ratios than the other types of plants. In addition, legumes increase soil nitrogen (N) supply, which could make N less limiting to other species and potentially decrease their investment in roots. The negative warming × diversity interaction on root mass led to an overall negative interactive effect of these two global change factors on the sum of above and belowground biomass, and thus likely on total plant carbon stores. In total, plant diversity increased the effect of warming on aboveground net productivity and moderated the effect on root mass. These divergent effects suggest that warming and changes in plant diversity are likely to have both interactive and divergent impacts on various aspects of ecosystem functioning. © 2015 John Wiley & Sons Ltd.

A warmer and wetter solution for early Mars and the challenges with transient warming

NASA Astrophysics Data System (ADS)

Ramirez, Ramses M.

2017-11-01

The climate of early Mars has been hotly debated for decades. Although most investigators believe that the geology indicates the presence of surface water, disagreement has persisted regarding how warm and wet the surface must have been and how long such conditions may have existed. Although the geologic evidence is most easily explained by a persistently warm climate, the perceived difficulty that climate models have in generating warm surface conditions has seeded various models that assume a cold and glaciated early Mars punctuated by transient warming episodes. However, I use a single-column radiative convective climate model to show that it is relatively more straightforward to satisfy warm and relatively non-glaciated early Mars conditions, requiring only ∼1% H2 and 3 bar CO2 or ∼20% H2 and 0.55 bar CO2. In contrast, the reflectivity of surface ice greatly increases the difficulty to transiently warm an initially frozen surface. Surface pressure thresholds required for warm conditions increase ∼10 - 60% for transient warming models, depending on ice cover fraction. No warm solution is possible for ice cover fractions exceeding 40%, 70%, and 85% for mixed snow/ice and 25%, 35%, and 49% for fresher snow/ice at H2 concentrations of 3%, 10%, and 20%, respectively. If high temperatures (298-323 K) were required to produce the observed surface clay amounts on a transiently warm early Mars (Bishop et al), I show that such temperatures would have required surface pressures that exceed available paleopressure constraints for nearly all H2 concentrations considered (1-20%). I then argue that a warm and semi-arid climate remains the simplest and most logical solution to Mars paleoclimate.

Sea Surface Warming and Increased Aridity at Mid-latitudes during Eocene Thermal Maximum 2

NASA Astrophysics Data System (ADS)

Harper, D. T.; Zeebe, R. E.; Hoenisch, B.; Schrader, C.; Lourens, L. J.; Zachos, J. C.

2017-12-01

Early Eocene hyperthermals, i.e. abrupt global warming events characterized by the release of isotopically light carbon to the atmosphere, can provide insight into the sensitivity of the Earth's climate system and hydrologic cycle to carbon emissions. Indeed, the largest Eocene hyperthermal, the Paleocene-Eocene Thermal Maximum (PETM), has provided one case study of extreme and abrupt global warming, with a mass of carbon release roughly equivalent to total modern fossil fuel reserves and a release rate 1/10 that of modern. Global sea surface temperatures (SST) increased by 5-8°C during the PETM and extensive evidence from marine and terrestrial records indicates significant shifts in the hydrologic cycle consistent with an increase in poleward moisture transport in response to surface warming. The second largest Eocene hyperthermal, Eocene Thermal Maximum 2 (ETM-2) provides an additional calibration point for determining the sensitivity of climate and the hydrologic cycle to massive carbon release. Marine carbon isotope excursions (CIE) and warming at the ETM-2 were roughly half as large as at the PETM, but reliable evidence for shifts in temperature and the hydrologic cycle are sparse for the ETM-2. Here, we utilize coupled planktic foraminiferal δ18O and Mg/Ca to determine ΔSST and ΔSSS (changes in sea surface temperature and salinity) for ETM-2 at ODP Sites 1209 (28°N paleolatitude in the Pacific) and 1265 (42°S paleolatitude in the S. Atlantic), accounting for potential pH influence on the two proxies by using LOSCAR climate-carbon cycle simulated ΔpH. Our results indicate a warming of 2-4°C at both mid-latitude sites and an increase in SSS of 1-3ppt, consistent with simulations of early Paleogene hydroclimate that suggest an increase in low- to mid-latitude aridity due to an intensification of moisture transport to high-latitudes. Furthermore, the magnitude of the CIE and warming for ETM-2 scales with the CIE and warming for the PETM, suggesting that the source of carbon was similar for both events.

Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice.

PubMed

Li, Xichen; Holland, David M; Gerber, Edwin P; Yoo, Changhyun

2014-01-23

In recent decades, Antarctica has experienced pronounced climate changes. The Antarctic Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land ice. Additionally, in contrast to the sea-ice decline over the Arctic, Antarctic sea ice has not declined, but has instead undergone a perplexing redistribution. Antarctic climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen-Bellingshausen-Weddell seas and to the Antarctic Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change.

Enhanced summer warming reduces fungal decomposer diversity and litter mass loss more strongly in dry than in wet tundra.

PubMed

Christiansen, Casper T; Haugwitz, Merian S; Priemé, Anders; Nielsen, Cecilie S; Elberling, Bo; Michelsen, Anders; Grogan, Paul; Blok, Daan

2017-01-01

Many Arctic regions are currently experiencing substantial summer and winter climate changes. Litter decomposition is a fundamental component of ecosystem carbon and nutrient cycles, with fungi being among the primary decomposers. To assess the impacts of seasonal climatic changes on litter fungal communities and their functioning, Betula glandulosa leaf litter was surface-incubated in two adjacent low Arctic sites with contrasting soil moisture regimes: dry shrub heath and wet sedge tundra at Disko Island, Greenland. At both sites, we investigated the impacts of factorial combinations of enhanced summer warming (using open-top chambers; OTCs) and deepened snow (using snow fences) on surface litter mass loss, chemistry and fungal decomposer communities after approximately 1 year. Enhanced summer warming significantly restricted litter mass loss by 32% in the dry and 17% in the wet site. Litter moisture content was significantly reduced by summer warming in the dry, but not in the wet site. Likewise, fungal total abundance and diversity were reduced by OTC warming at the dry site, while comparatively modest warming effects were observed in the wet site. These results suggest that increased evapotranspiration in the OTC plots lowered litter moisture content to the point where fungal decomposition activities became inhibited. In contrast, snow addition enhanced fungal abundance in both sites but did not significantly affect litter mass loss rates. Across sites, control plots only shared 15% of their fungal phylotypes, suggesting strong local controls on fungal decomposer community composition. Nevertheless, fungal community functioning (litter decomposition) was negatively affected by warming in both sites. We conclude that although buried soil organic matter decomposition is widely expected to increase with future summer warming, surface litter decay and nutrient turnover rates in both xeric and relatively moist tundra are likely to be significantly restricted by the evaporative drying associated with warmer air temperatures. © 2016 John Wiley & Sons Ltd.

Unabated global surface temperature warming: evaluating the evidence

NASA Astrophysics Data System (ADS)

Karl, T. R.; Arguez, A.

2015-12-01

New insights related to time-dependent bias corrections in global surface temperatures have led to higher rates of warming over the past few decades than previously reported in the IPCC Fifth Assessment Report (2014). Record high global temperatures in the past few years have also contributed to larger trends. The combination of these factors and new analyses of the rate of temperature change show unabated global warming since at least the mid-Twentieth Century. New time-dependent bias corrections account for: (1) differences in temperatures measured from ships and drifting buoys; (2) improved corrections to ship measured temperatures; and (3) the larger rates of warming in polar regions (particularly the Arctic). Since 1951, the period over which IPCC (2014) attributes over half of the observed global warming to human causes, it is shown that there has been a remarkably robust and sustained warming, punctuated with inter-annual and decadal variability. This finding is confirmed through simple trend analysis and Empirical Mode Decomposition (EMD). Trend analysis however, especially for decadal trends, is sensitive to selection bias of beginning and ending dates. EMD has no selection bias. Additionally, it can highlight both short- and long-term processes affecting the global temperature times series since it addresses both non-linear and non-stationary processes. For the new NOAA global temperature data set, our analyses do not support the notion of a hiatus or slowing of long-term global warming. However, sub-decadal periods of little (or no warming) and rapid warming can also be found, clearly showing the impact of inter-annual and decadal variability that previously has been attributed to both natural and human-induced non-greenhouse forcings.

Effects of warming on the structure and function of a boreal black spruce forest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stith T.Gower

2010-03-03

A strong argument can be made that there is a greater need to study the effect of warming on boreal forests more than on any other terrestrial biome. Boreal forests, the second largest forest biome, are predicted to experience the greatest warming of any forest biome in the world, but a process-based understanding of how warming will affect the structure and function of this economically and ecologically important forest biome is lacking. The effects of warming on species composition, canopy structure and biogeochemical cycles are likely to be complex; elucidating the underlying mechanisms will require long-term whole-ecosystem manipulation to capturemore » all the complex feedbacks (Shaver et al. 2000, Rustad et al. 2001, Stromgren 2001). The DOE Program for Ecosystem Research funded a three year project (2002-2005) to use replicated heated chambers on soil warming plots in northern Manitoba to examine the direct effects of whole-ecosystem warming. We are nearing completion of our first growing season of measurements (fall 2004). In spite of the unforeseen difficulty of installing the heating cable, our heating and irrigation systems worked extremely well, maintaining environmental conditions within 5-10% of the specified design 99% of the time. Preliminary data from these systems, all designed and built by our laboratory at the University of Wisconsin, support our overall hypothesis that warming will increase the carbon sink strength of upland boreal black spruce forests. I request an additional three years of funding to continue addressing the original objectives: (1) Examine the effect of warming on phenology of overstory, understory and bryophyte strata. Sap flux systems and dendrometer bands, monitored by data loggers, will be used to quantify changes in phenology and water use. (2) Quantify the effects of warming on nitrogen and water use by overstory, understory and bryophytes. (3) Compare effects of warming on autotrophic respiration and above- and belowground net primary production (NPP) budgets. Autotrophic respiration budgets will be constructed using chamber measurements for each tissue and NPP and standard allometry techniques (Gower et al. 1999). (4) Compare microbial and root dynamics, and net soil surface CO2 flux, of control and warmed soils to identify causes that may explain the hypothesized minimal effect of soil warming on soil surface CO2 flux. Fine root production and turnover will be quantified using minirhizotrons, and microbial dynamics will be determined using laboratory mineralization incubations. Soil surface CO2 flux will be measured using automated soil surface CO2 flux systems and portable CO2 analyzers. The proposed study builds on the existing research programs Gower has in northern Manitoba and would not be possible without in-kind services and financial support from Manitoba Hydro and University of Wisconsin.« less

Climate, ocean circulation, and sea level changes under stabilization and overshoot pathways to 1.5 K warming

NASA Astrophysics Data System (ADS)

Palter, Jaime B.; Frölicher, Thomas L.; Paynter, David; John, Jasmin G.

2018-06-01

The Paris Agreement has initiated a scientific debate on the role that carbon removal - or net negative emissions - might play in achieving less than 1.5 K of global mean surface warming by 2100. Here, we probe the sensitivity of a comprehensive Earth system model (GFDL-ESM2M) to three different atmospheric CO2 concentration pathways, two of which arrive at 1.5 K of warming in 2100 by very different pathways. We run five ensemble members of each of these simulations: (1) a standard Representative Concentration Pathway (RCP4.5) scenario, which produces 2 K of surface warming by 2100 in our model; (2) a stabilization pathway in which atmospheric CO2 concentration never exceeds 440 ppm and the global mean temperature rise is approximately 1.5 K by 2100; and (3) an overshoot pathway that passes through 2 K of warming at mid-century, before ramping down atmospheric CO2 concentrations, as if using carbon removal, to end at 1.5 K of warming at 2100. Although the global mean surface temperature change in response to the overshoot pathway is similar to the stabilization pathway in 2100, this similarity belies several important differences in other climate metrics, such as warming over land masses, the strength of the Atlantic Meridional Overturning Circulation (AMOC), ocean acidification, sea ice coverage, and the global mean sea level change and its regional expressions. In 2100, the overshoot ensemble shows a greater global steric sea level rise and weaker AMOC mass transport than in the stabilization scenario, with both of these metrics close to the ensemble mean of RCP4.5. There is strong ocean surface cooling in the North Atlantic Ocean and Southern Ocean in response to overshoot forcing due to perturbations in the ocean circulation. Thus, overshoot forcing in this model reduces the rate of sea ice loss in the Labrador, Nordic, Ross, and Weddell seas relative to the stabilized pathway, suggesting a negative radiative feedback in response to the early rapid warming. Finally, the ocean perturbation in response to warming leads to strong pathway dependence of sea level rise in northern North American cities, with overshoot forcing producing up to 10 cm of additional sea level rise by 2100 relative to stabilization forcing.

Air-sea heat flux climatologies in the Mediterranean Sea: Surface energy balance and its consistency with ocean heat storage

NASA Astrophysics Data System (ADS)

Song, Xiangzhou; Yu, Lisan

2017-05-01

This study provides an analysis of the Mediterranean Sea surface energy budget using nine surface heat flux climatologies. The ensemble mean estimation shows that the net downward shortwave radiation (192 ± 19 W m-2) is balanced by latent heat flux (-98 ± 10 W m-2), followed by net longwave radiation (-78 ± 13 W m-2) and sensible heat flux (-13 ± 4 W m-2). The resulting net heat budget (Qnet) is 2 ± 12 W m-2 into the ocean, which appears to be warm biased. The annual-mean Qnet should be -5.6 ± 1.6 W m-2 when estimated from the observed net transport through the Strait of Gibraltar. To diagnose the uncertainty in nine Qnet climatologies, we constructed Qnet from the heat budget equation by using historic hydrological observations to determine the heat content changes and advective heat flux. We also used the Qnet from a data-assimilated global ocean state estimation as an additional reference. By comparing with the two reference Qnet estimates, we found that seven products (NCEP 1, NCEP 2, CFSR, ERA-Interim, MERRA, NOCSv2.0, and OAFlux+ISCCP) overestimate Qnet, with magnitude ranging from 6 to 27 W m-2, while two products underestimate Qnet by -6 W m-2 (JRA55) and -14 W m-2 (CORE.2). Together with the previous warm pool work of Song and Yu (2013), we show that CFSR, MERRA, NOCSv2.0, and OAFlux+ISCCP are warm-biased not only in the western Pacific warm pool but also in the Mediterranean Sea, while CORE.2 is cold-biased in both regions. The NCEP 1, 2, and ERA-Interim are cold-biased over the warm pool but warm-biased in the Mediterranean Sea.

The Effect of Impacts on the Early Martian Climate

NASA Technical Reports Server (NTRS)

Colaprete, A.; Haberle, R. M.; Segura, T. L.; Toon, O. B.; Zahnle, K.

2004-01-01

The first images returned by the Mariner 7 spacecraft of the Martian surface showed a landscape heavily scared by impacts. Mariner 9 imaging revealed geomorphic features including valley networks and outflow channels that suggest liquid water once flowed at the surface of Mars. Further evidence for water erosion and surface modification has come from the Viking Spacecraft, Mars Pathfinder, Mars Global Surveyor's (MGS) Mars Orbiter Camera (MOC), and Mars Odyssey's THEMIS instrument. In addition to network channels, this evidence includes apparent paleolake beds, fluvial fans and sedimentary layers. The estimated erosion rates necessary to explain the observed surface morphologies present a conundrum. The rates of erosion appear to be highest when the early sun was fainter and only 75% as luminous as it is today. All of this evidence points to a very different climate than what exists on Mars today. The most popular paradigm for the formation of the valley networks is that Mars had at one time a warm (T average > 273), wetter and stable climate. Possible warming mechanisms have included increased surface pressures, carbon dioxide clouds and trace greenhouse gasses. Yet to date climate models have not been able to produce a continuously warm and wet early Mars. The rates of erosion appear to correlate with the rate at which Mars was impacted thus an alternate possibility is transient warm and wet conditions initiated by large impacts. It is widely accepted that even relatively small impacts (approx. 10 km) have altered the past climate of Earth to such an extent as to cause mass extinctions. Mars has been impacted with a similar distribution of objects. The impact record at Mars is preserved in the abundance of observable craters on it surface. Impact induced climate change must have occurred on Mars.

Investigations of Heat Transfer in Vacuum between Room Temperature and 80 K

NASA Astrophysics Data System (ADS)

Hooks, J.; Demko, J. A.; E Fesmire, J.; Matsumoto, T.

2017-12-01

The heat transfer between room temperature and 80 K is controlled using various insulating material combinations. The modes of heat transfer are well established to be conduction and thermal radiation when in a vacuum. Multi-Layer Insulation (MLI) in a vacuum has long been the best approach. Typically this layered system is applied to the cold surface. This paper investigates the application of MLI to both the cold and warm surface to see whether there is a significant difference. In addition if MLI is on the warm surface, the cold side of the MLI may be below the critical temperature of some high temperature superconducting (HTS) materials. It has been proposed that HTS materials can serve to block thermal radiation. An experiment is conducted to measure this effect. Boil-off calorimetry is the method of measuring the heat transfer.

Sensitivity of the Palaeocene-Eocene Thermal Maximum climate to cloud properties.

PubMed

Kiehl, Jeffrey T; Shields, Christine A

2013-10-28

The Palaeocene-Eocene Thermal Maximum (PETM) was a significant global warming event in the Earth's history (approx. 55 Ma). The cause for this warming event has been linked to increases in greenhouse gases, specifically carbon dioxide and methane. This rapid warming took place in the presence of the existing Early Eocene warm climate. Given that projected business-as-usual levels of atmospheric carbon dioxide reach concentrations of 800-1100 ppmv by 2100, it is of interest to study past climates where atmospheric carbon dioxide was higher than present. This is especially the case given the difficulty of climate models in simulating past warm climates. This study explores the sensitivity of the simulated pre-PETM and PETM periods to change in cloud condensation nuclei (CCN) and microphysical properties of liquid water clouds. Assuming lower levels of CCN for both of these periods leads to significant warming, especially at high latitudes. The study indicates that past differences in cloud properties may be an important factor in accurately simulating past warm climates. Importantly, additional shortwave warming from such a mechanism would imply lower required atmospheric CO2 concentrations for simulated surface temperatures to be in reasonable agreement with proxy data for the Eocene.

TOPEX/El Nino Watch - El Nino Warm Water Pool Decreasing, Jan, 08, 1998

NASA Technical Reports Server (NTRS)

1998-01-01

This image of the Pacific Ocean was produced using sea surface height measurements taken by the U.S.-French TOPEX/Poseidon satellite. The image shows sea surface height relative to normal ocean conditions on Jan. 8, 1998, and sea surface height is an indicator of the heat content of the ocean. The volume of the warm water pool related to the El Nino has decreased by about 40 percent since its maximum in early November, but the area of the warm water pool is still about one and a half times the size of the continental United States. The volume measurements are computed as the sum of all the sea surface height changes as compared to normal ocean conditions. In addition, the maximum water temperature in the eastern tropical Pacific, as measured by the National Oceanic and Atmospheric Administration (NOAA), is still higher than normal. Until these high temperatures diminish, the El Nino warm water pool still has great potential to disrupt global weather because the high water temperatures directly influence the atmosphere. Oceanographers believe the recent decrease in the size of the warm water pool is a normal part of El Nino's natural rhythm. TOPEX/Poseidon has been tracking these fluctuations of the El Nino warm pool since it began in early 1997. These sea surface height measurements have provided scientists with their first detailed view of how El Nino's warm pool behaves because the TOPEX/Poseidon satellite measures the changing sea surface height with unprecedented precision. In this image, the white and red areas indicate unusual patterns of heat storage; in the white areas, the sea surface is between 14 and 32 centimeters (6 to 13 inches) above normal; in the red areas, it's about 10 centimeters (4 inches) above normal. The green areas indicate normal conditions, while purple (the western Pacific) means at least 18 centimeters (7 inches) below normal sea level.

The El Nino phenomenon is thought to be triggered when the steady westward blowing trade winds weaken and even reverse direction. This change in the winds allows a large mass of warm water (the red and white area) that is normally located near Australia to move eastward along the equator until it reaches the coast of South America. The displacement of so much warm water affects evaporation, where rain clouds form and, consequently, alters the typical atmospheric jet stream patterns around the world. Using these global data, limited regional measurements from buoys and ships, and a forecasting model of the ocean-atmosphere system, the National Centers for Environmental Prediction (NCEP) of the National Oceanic and Atmospheric Administration, (NOAA), has issued an advisory indicating the presence of a strong El Nino condition throughout the winter.

For more information, please visit the TOPEX/Poseidon project web page at http://topex-www.jpl.nasa.gov

[A comparison of the effects of intravenous fluid warming and skin surface warming on peri-operative body temperature and acid base balance of elderly patients with abdominal surgery].

PubMed

Park, Hyosun; Yoon, Haesang

2007-12-01

The purpose of this study was to compare the effects of intravenous fluid warming and skin surface warming on peri-operative body temperature and acid base balance of abdominal surgical patients under general anesthesia. Data collection was performed from January 4th, to May 31, 2004. The intravenous fluid warming(IFW) group (30 elderly patients) was warmed through an IV line by an Animec set to 37 degrees C. The skin surface warming (SSW) group (30 elderly patients) was warmed by a circulating-water blanket set to 38 degrees C under the back and a 60W heating lamp 40 cm above the chest. The warming continued from induction of general anesthesia to two hours after completion of surgery. Collected data was analyzed using Repeated Measures ANOVA, and Bonferroni methods. SSW was more effective than IFW in preventing hypothermia(p= .043), preventing a decrease of HCO(3)(-)(p= .000) and preventing base excess (p= .000) respectively. However, there was no difference in pH between the SSW and IFW (p= .401) groups. We conclude that skin surface warming is more effective in preventing hypothermia, and HCO(3)(-) and base excess during general anesthesia, and returning to normal body temperature after surgery than intravenous fluid warming; however, skin surface warming wasn't able to sustain a normal body temperature in elderly patients undergoing abdominal surgery under general anesthesia.

Polar Research with Unmanned Aircraft and Tethered Balloons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivey, M; Petty, R; Desilets, D

2014-01-24

The Arctic is experiencing rapid climate change, with nearly double the rate of surface warming observed elsewhere on the planet. While various positive feedback mechanisms have been suggested, the reasons for Arctic amplification are not well understood, nor are the impacts to the global carbon cycle well quantified. Additionally, there are uncertainties associated with the complex interactions between Earth’s surface and the atmosphere. Elucidating the causes and consequences of Arctic warming is one of the many goals of the Climate and Environmental Sciences Division (CESD) of the U.S. Department of Energy’s (DOE) Biological and Environmental Research (BER) program, and ismore » part of the larger CESD initiative to develop a robust predictive understanding of Earth’s climate system.« less

Evolution of CO2 and H2O on Mars: A cold Early History?

NASA Technical Reports Server (NTRS)

Niles, P. B.; Michalski, J.

2011-01-01

The martian climate has long been thought to have evolved substantially through history from a warm and wet period to the current cold and dry conditions on the martian surface. This view has been challenged based primarily on evidence that the early Sun had a substantially reduced luminosity and that a greenhouse atmosphere would be difficult to sustain on Mars for long periods of time. In addition, the evidence for a warm, wet period of martian history is far from conclusive with many of the salient features capable of being explained by an early cold climate. An important test of the warm, wet early Mars hypothesis is the abundance of carbonates in the crust [1]. Recent high precision isotopic measurements of the martian atmosphere and discoveries of carbonates on the martian surface provide new constraints on the evolution of the martian atmosphere. This work seeks to apply these constraints to test the feasibility of the cold early scenario

The December 2015 North Pole Warming Event and the Increasing Occurrence of Such Events

PubMed Central

Moore, G. W. K.

2016-01-01

In late December 2015, widespread media interest revolved around forecasts that the surface air temperature at the North Pole would rise above freezing. Although there has been significant interest in the enhanced warming that is occurring at high northern latitudes, a process known as arctic amplification, remarkably little is known about these midwinter warming events at the pole including their frequency, duration and magnitude as well as the environmental conditions responsible for their occurrence. Here we use buoy and radiosonde data along with operational weather forecasts and atmospheric reanalyses to show that such events are associated with surface cyclones near the pole as well as a highly perturbed polar vortex. They occur once or twice each decade with the earliest identified event taking place in 1959. In addition, the warmest midwinter temperatures at the North Pole have been increasing at a rate that is twice as large as that for mean midwinter temperatures at the pole. It is argued that this enhanced trend is consistent with the loss of winter sea ice from the Nordic Seas that moves the reservoir of warm air over this region northwards making it easier for weather systems to transport this heat polewards. PMID:27976745

Abrupt warming of the Red Sea

NASA Astrophysics Data System (ADS)

Raitsos, D. E.; Hoteit, I.; Prihartato, P. K.; Chronis, T.; Triantafyllou, G.; Abualnaja, Y.

2011-07-01

Coral reef ecosystems, often referred to as “marine rainforests,” concentrate the most diverse life in the oceans. Red Sea reef dwellers are adapted in a very warm environment, fact that makes them vulnerable to further and rapid warming. The detection and understanding of abrupt temperature changes is an important task, as ecosystems have more chances to adapt in a slowly rather than in a rapid changing environment. Using satellite derived sea surface and ground based air temperatures, it is shown that the Red Sea is going through an intense warming initiated in the mid-90s, with evidence for an abrupt increase after 1994 (0.7°C difference pre and post the shift). The air temperature is found to be a key parameter that influences the Red Sea marine temperature. The comparisons with Northern Hemisphere temperatures revealed that the observed warming is part of global climate change trends. The hitherto results also raise additional questions regarding other broader climatic impacts over the area.

Long-terms Change of Sea Surface Temperature in the South China Sea

NASA Astrophysics Data System (ADS)

Park, Y. G.; Choi, A.

2016-02-01

Using the Hadley Centre Global Sea Ice and Sea Surface Temperature (HadISST) the long term trend in the South China Sea (SCS) sea surface temperature (SST) between 1950 and 2008 is investigated. Both in winter and summer SST was increased by comparable amounts, but the warming patterns and the governing processes was different. During winter warming rate was greater in the deep basin in the central part, while during summer near the southern part. In winter the net heat flux into the sea was increased and could contribute to the warming. The pattern of the heat flux, however, was different from that of the warming. The heat flux was increased over the coastal area where warming was weaker, but decreased in deeper part where warming was stronger. The northeasterly monsoon wind weakened to lower the shoreward Ekman transport and the sea surface height gradient. The cyclonic gyre that transports cold northern water to south was weakened to warm the ocean. The effect manifested more strongly southward western boundary currents, and subsequently cold advection. In summer the net surface heat flux, however, was reduced and could not contribute to the warming. Over the southern part of the ocean the weakening of the southwesterly summer monsoon reduced southeastward Ekman transport, which is antiparallel to the mean SST gradient. Firstly, southeastward cold advection is reduced to warm the surface near the southeastern boundary of the SCS. The upwelling southeast of Vietnam was also weakened to raise the SST east of Vietnam. Thus the weakening of the wind in each season was the ultimate cause of the warming, but the responses of the ocean that lead to the warming were different.

Experimental and ecosystem model approach to assessing the sensitivity of High arctic deep permafrost to changes in surface temperature and precipitation

NASA Astrophysics Data System (ADS)

Rasmussen, L. H.; Zhang, W.; Elberling, B.; Cable, S.

2016-12-01

Permafrost affected areas in Greenland are expected to experience large temperature increases within the 21st century. Most previous studies on permafrost consider near-surface soil, where changes will happen first. However, how sensitive the deep permafrost temperature is to near-surface conditions through changes in soil thermal properties, snow depth and soil moisture, is not known. In this study, we measured the sensitivity of thermal conductivity (TC) to gravimetric water content (GWC) in frozen and thawed deep permafrost sediments from deltaic, alluvial and fluvial depositional environments in the Zackenberg valley, NE Greenland. We also calibrated a coupled heat and water transfer model, the "CoupModel", for the two closely situated deltaic sites, one with average snow depth and the other with topographic snow accumulation. With the calibrated model, we simulated deep permafrost thermal dynamics in four scenarios with changes in surface forcing: a. 3 °C warming and 20 % increase in precipitation; b. 3 °C warming and 100 % increase in precipitation; c. 6 °C warming and 20 % increase in precipitation; d. 6 °C warming and 100 % increase in precipitation.Our results indicated that frozen sediments had higher TC than thawed sediments. All sediments showed a positive linear relation between TC and soil moisture when frozen, and a logarithmic one when thawed. Fluvial sediments had high sensitivity, but never reached above 12 % GWC, indicating a field effect of water retention capacity. Alluvial sediments were less sensitive to soil moisture than deltaic and fluvial sediments, indicating the importance of unfrozen water in frozen sediment. The deltaic site with snow accumulation had 1 °C higher annual mean ground temperature than the average snow site. The soil temperature at the depth of 18 m increased with 1.5 °C and 3.5 °C in the scenarios with 3 °C and 6 °C warming, respectively. Precipitation had no significant additional effect to warming. We conclude that below-ground sediment properties affect the sensitivity of TC to GWC, that surface temperature changes can significantly affect the deep permafrost within a short period, and that differences in snow depth affect surface temperatures. Geology, pedology and precipitation should thus be considered if estimating future High arctic deep permafrost sensitivity.

Can biomass responses to warming at plant to ecosystem levels be predicted by leaf-level responses?

NASA Astrophysics Data System (ADS)

Xia, J.; Shao, J.; Zhou, X.; Yan, W.; Lu, M.

2015-12-01

Global warming has the profound impacts on terrestrial C processes from leaf to ecosystem scales, potentially feeding back to climate dynamics. Although numerous studies had investigated the effects of warming on C processes from leaf to plant and ecosystem levels, how leaf-level responses to warming scale up to biomass responses at plant, population, and community levels are largely unknown. In this study, we compiled a dataset from 468 papers at 300 experimental sites and synthesized the warming effects on leaf-level parameters, and plant, population and ecosystem biomass. Our results showed that responses of plant biomass to warming mainly resulted from the changed leaf area rather than the altered photosynthetic capacity. The response of ecosystem biomass to warming was weaker than those of leaf area and plant biomass. However, the scaling functions from responses of leaf area to plant biomass to warming were different in diverse forest types, but functions were similar in non-forested biomes. In addition, it is challenging to scale the biomass responses from plant up to ecosystem. These results indicated that leaf area might be the appropriate index for plant biomass response to warming, and the interspecific competition might hamper the scaling of the warming effects on plant and ecosystem levels, suggesting that the acclimation capacity of plant community should be incorporated into land surface models to improve the prediction of climate-C cycle feedback.

Striking Seasonality in the Secular Warming of the Northern Continents: Structure and Mechanisms

NASA Astrophysics Data System (ADS)

Nigam, S.; Thomas, N. P.

2017-12-01

The linear trend in twentieth-century surface air temperature (SAT)—a key secular warming signal— exhibits striking seasonal variations over Northern Hemisphere continents; SAT trends are pronounced in winter and spring but notably weaker in summer and fall. The SAT trends in historical twentieth-century climate simulations informing the Intergovernmental Panel for Climate Change's Fifth Assessment show varied (and often unrealistic) strength and structure, and markedly weaker seasonal variation. The large intra-ensemble spread of winter SAT trends in some historical simulations was surprising, especially in the context of century-long linear trends, with implications for the detection of the secular warming signal. The striking seasonality of observed secular warming over northern continents warrants an explanation and the representation of related processes in climate models. Here, the seasonality of SAT trends over North America is shown to result from land surface-hydroclimate interactions and, to an extent, also from the secular change in low-level atmospheric circulation and related thermal advection. It is argued that the winter dormancy and summer vigor of the hydrologic cycle over middle- to high-latitude continents permit different responses to the additional incident radiative energy from increasing greenhouse gas concentrations. The seasonal cycle of climate, despite its monotony, provides an expanded phase space for the exposition of the dynamical and thermodynamical processes generating secular warming, and an exceptional cost-effective opportunity for benchmarking climate projection models.

Evolution of surface sensible heat over the Tibetan Plateau under the recent global warming hiatus

NASA Astrophysics Data System (ADS)

Zhu, Lihua; Huang, Gang; Fan, Guangzhou; Qu, Xia; Zhao, Guijie; Hua, Wei

2017-10-01

Based on regular surface meteorological observations and NCEP/DOE reanalysis data, this study investigates the evolution of surface sensible heat (SH) over the central and eastern Tibetan Plateau (CE-TP) under the recent global warming hiatus. The results reveal that the SH over the CE-TP presents a recovery since the slowdown of the global warming. The restored surface wind speed together with increased difference in ground-air temperature contribute to the recovery in SH. During the global warming hiatus, the persistent weakening wind speed is alleviated due to the variation of the meridional temperature gradient. Meanwhile, the ground surface temperature and the difference in ground-air temperature show a significant increasing trend in that period caused by the increased total cloud amount, especially at night. At nighttime, the increased total cloud cover reduces the surface effective radiation via a strengthening of atmospheric counter radiation and subsequently brings about a clear upward trend in ground surface temperature and the difference in ground-air temperature. Cloud-radiation feedback plays a significant role in the evolution of the surface temperature and even SH during the global warming hiatus. Consequently, besides the surface wind speed, the difference in ground-air temperature becomes another significant factor for the variation in SH since the slowdown of global warming, particularly at night.

Temperature and size variabilities of the Western Pacific Warm Pool

NASA Technical Reports Server (NTRS)

Yan, Xiao-Hai; Ho, Chung-Ru; Zheng, Quanan; Klemas, Vic

1992-01-01

Variabilities in sea-surface temperature and size of the Western Pacific Warm Pool were tracked with 10 years of satellite multichannel sea-surface temperature observations from 1982 to 1991. The results show that both annual mean sea-surface temperature and the size of the warm pool increased from 1983 to 1987 and fluctuated after 1987. Possible causes of these variations include solar irradiance variabilities, El Nino-Southern Oscillaton events, volcanic activities, and global warming.

Early 20th Century Arctic Warming Intensified by Pacific and Atlantic Multidecadal Variability

NASA Astrophysics Data System (ADS)

Tokinaga, H.; Xie, S. P.; Mukougawa, H.

2017-12-01

We investigate the influence of Pacific and Atlantic multidecadal variability on the Arctic temperature, with a particular focus on the early 20th century Arctic warming. Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing than at present. We find that the concurrent phase shift of Pacific and Atlantic multidecadal variability is the major driver for the early 20th century Arctic warming. Atmospheric model simulations reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early Arctic warming is associated with the cold-to-warm phase shifts of Atlantic and Pacific multidecadal variability modes, a SST pattern reminiscent of the positive phase of the Pacific decadal and Atlantic multidecadal oscillations. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. The equatorial Pacific warming deepens the Aleutian low, advecting warm air to the North American Arctic. Coupled ocean-atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, cold-to-warm phase shift of the Pacific and Atlantic multidecadal variability. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region.

Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

NASA Astrophysics Data System (ADS)

Tokinaga, Hiroki; Xie, Shang-Ping; Mukougawa, Hitoshi

2017-06-01

With amplified warming and record sea ice loss, the Arctic is the canary of global warming. The historical Arctic warming is poorly understood, limiting our confidence in model projections. Specifically, Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing. Here, we show that the concurrent phase shift of Pacific and Atlantic interdecadal variability modes is the major driver for the rapid early 20th-century Arctic warming. Atmospheric model simulations successfully reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early 20th-century Arctic warming is associated with positive SST anomalies over the tropical and North Atlantic and a Pacific SST pattern reminiscent of the positive phase of the Pacific decadal oscillation. Atmospheric circulation changes are important for the early 20th-century Arctic warming. The equatorial Pacific warming deepens the Aleutian low, advecting warm air into the North American Arctic. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. Coupled ocean-atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, negative-to-positive phase shift of the Pacific and Atlantic interdecadal modes. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region.

Controls on the Archean climate system investigated with a global climate model.

PubMed

Wolf, E T; Toon, O B

2014-03-01

The most obvious means of resolving the faint young Sun paradox is to invoke large quantities of greenhouse gases, namely, CO2 and CH4. However, numerous changes to the Archean climate system have been suggested that may have yielded additional warming, thus easing the required greenhouse gas burden. Here, we use a three-dimensional climate model to examine some of the factors that controlled Archean climate. We examine changes to Earth's rotation rate, surface albedo, cloud properties, and total atmospheric pressure following proposals from the recent literature. While the effects of increased planetary rotation rate on surface temperature are insignificant, plausible changes to the surface albedo, cloud droplet number concentrations, and atmospheric nitrogen inventory may each impart global mean warming of 3-7 K. While none of these changes present a singular solution to the faint young Sun paradox, a combination can have a large impact on climate. Global mean surface temperatures at or above 288 K could easily have been maintained throughout the entirety of the Archean if plausible changes to clouds, surface albedo, and nitrogen content occurred.

Regional seasonal warming anomalies and land-surface feedbacks

NASA Astrophysics Data System (ADS)

Coffel, E.; Horton, R. M.

2017-12-01

Significant seasonal variations in warming are projected in some regions, especially central Europe, the southeastern U.S., and central South America. Europe in particular may experience up to 2°C more warming during June, July, and August than in the annual mean, enhancing the risk of extreme summertime heat. Previous research has shown that heat waves in Europe and other regions are tied to seasonal soil moisture variations, and that in general land-surface feedbacks have a strong effect on seasonal temperature anomalies. In this study, we show that the seasonal anomalies in warming are also due in part to land-surface feedbacks. We find that in regions with amplified warming during the hot season, surface soil moisture levels generally decline and Bowen ratios increase as a result of a preferential partitioning of incoming energy into sensible vs. latent. The CMIP5 model suite shows significant variability in the strength of land-atmosphere coupling and in projections of future precipitation and soil moisture. Due to the dependence of seasonal warming on land-surface processes, these inter-model variations influence the projected summertime warming amplification and contribute to the uncertainty in projections of future extreme heat.

Mechanisms controlling the dependence of surface warming on cumulative carbon emissions over the next century in a suite of Earth system models

NASA Astrophysics Data System (ADS)

Williams, Richard; Roussenov, Vassil; Goodwin, Philip; Resplandy, Laure; Bopp, Laurent

2017-04-01

Insight into how to avoid dangerous climate may be obtained from Earth system model projections, which reveal a near-linear dependence of global-mean surface warming on cumulative carbon emissions. This dependence of surface warming on carbon emissions is interpreted in terms of a product of three terms: the dependence of surface warming on radiative forcing, the fractional radiative forcing contribution from atmospheric CO2 and the dependence of radiative forcing from atmospheric CO2 on cumulative carbon emissions. Mechanistically each of these dependences varies, respectively, with ocean heat uptake, the CO2 and non-CO2 radiative forcing, and the ocean and terrestrial uptake of carbon. An ensemble of 9 Earth System models forced by up to 4 Representative Concentration Pathways are diagnosed. In all cases, the dependence of surface warming on carbon emissions evolves primarily due to competing effects of heat and carbon uptake over the upper ocean: there is a reduced effect of radiative forcing from CO2 due to ocean carbon uptake, which is partly compensated by enhanced surface warming due to a reduced effect of ocean heat uptake. There is a wide spread in the dependence of surface warming on carbon emissions, undermining the ability to identify the maximum permitted carbon emission to avoid dangerous climate. Our framework reveals how uncertainty in the future warming trend is high over the next few decades due to relatively high uncertainties in ocean heat uptake, non-CO2 radiative forcing and the undersaturation of carbon in the ocean.

Evaluation of evapotranspiration on paddy rice using non-weighting lysimeters under the different air temperature

NASA Astrophysics Data System (ADS)

Oh, D.; Ryu, J. H.; Cho, J.

2017-12-01

Estimation of the crop evapotranspiration (ETc), as a representative of crop water needs, is important for not only high crop productivity, but also improving irrigation water management. In farm lands crop coefficient (Kc), the ratio of ETc to potential ET, is often used to simply estiamte ETc. However, the traits of Kc under the global warming condition will different with current one because plant transpiration and surface evaporaiton will be changed by the alternative crop growth and evaporative energy. In this study, Non-Weighting Lysimeter (NWL) was used to directly estimate ETc under the warmed condition, particularly for paddy riace which has one of lower water use efficiency. The different air t emperature (Ta) conditions for the NWL were provided by Temperature Gradient Chamber (TGC), which was formed gradually warmed conditions. The water body evporation and paddy rice evapotransipiration in the NWL were at the two places of ambient Ta (AT) and AT+3° in the TGC. In addition, we installed Infra-Red thermometer (IRT) to understand the surface energy balance. The result was shown that the different partitioning of evaporation and transpiration of paddy rice at the AT+3°, comparing at AT. Further, the water use efficiency, the ratio of yield to total ET, was also decreased in the warmed condition. These experiments for paddy rice ET in the warmed conditions during growth period will be useful to understand the effect of global warming on the hydrological cycle and manamge the irrigation schedule for more efficient water use.

Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions

PubMed Central

Zeebe, Richard E.

2013-01-01

Climate sensitivity measures the response of Earth’s surface temperature to changes in forcing. The response depends on various climate processes that feed back on the initial forcing on different timescales. Understanding climate sensitivity is fundamental to reconstructing Earth’s climatic history as well as predicting future climate change. On timescales shorter than centuries, only fast climate feedbacks including water vapor, lapse rate, clouds, and snow/sea ice albedo are usually considered. However, on timescales longer than millennia, the generally higher Earth system sensitivity becomes relevant, including changes in ice sheets, vegetation, ocean circulation, biogeochemical cycling, etc. Here, I introduce the time-dependent climate sensitivity, which unifies fast-feedback and Earth system sensitivity. I show that warming projections, which include a time-dependent climate sensitivity, exhibit an enhanced feedback between surface warming and ocean CO2 solubility, which in turn leads to higher atmospheric CO2 levels and further warming. Compared with earlier studies, my results predict a much longer lifetime of human-induced future warming (23,000–165,000 y), which increases the likelihood of large ice sheet melting and major sea level rise. The main point regarding the legacy of anthropogenic greenhouse gas emissions is that, even if the fast-feedback sensitivity is no more than 3 K per CO2 doubling, there will likely be additional long-term warming from slow climate feedbacks. Time-dependent climate sensitivity also helps explaining intense and prolonged warming in response to massive carbon release as documented for past events such as the Paleocene–Eocene Thermal Maximum. PMID:23918402

Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions.

PubMed

Zeebe, Richard E

2013-08-20

Climate sensitivity measures the response of Earth's surface temperature to changes in forcing. The response depends on various climate processes that feed back on the initial forcing on different timescales. Understanding climate sensitivity is fundamental to reconstructing Earth's climatic history as well as predicting future climate change. On timescales shorter than centuries, only fast climate feedbacks including water vapor, lapse rate, clouds, and snow/sea ice albedo are usually considered. However, on timescales longer than millennia, the generally higher Earth system sensitivity becomes relevant, including changes in ice sheets, vegetation, ocean circulation, biogeochemical cycling, etc. Here, I introduce the time-dependent climate sensitivity, which unifies fast-feedback and Earth system sensitivity. I show that warming projections, which include a time-dependent climate sensitivity, exhibit an enhanced feedback between surface warming and ocean CO2 solubility, which in turn leads to higher atmospheric CO2 levels and further warming. Compared with earlier studies, my results predict a much longer lifetime of human-induced future warming (23,000-165,000 y), which increases the likelihood of large ice sheet melting and major sea level rise. The main point regarding the legacy of anthropogenic greenhouse gas emissions is that, even if the fast-feedback sensitivity is no more than 3 K per CO2 doubling, there will likely be additional long-term warming from slow climate feedbacks. Time-dependent climate sensitivity also helps explaining intense and prolonged warming in response to massive carbon release as documented for past events such as the Paleocene-Eocene Thermal Maximum.

Geothermal Heating, Convective Flow and Ice Thickness on Mars

NASA Technical Reports Server (NTRS)

Rosenberg, N. D.; Travis, B. J.; Cuzzi, J.

2001-01-01

Our 3D calculations suggest that hydrothermal circulation may occur in the martian regolith and may significantly thin the surface ice layer on Mars at some locations due to the upwelling of warm convecting fluids driven solely by background geothermal heating. Additional information is contained in the original extended abstract.

Ocean Heat Uptake Slows 21st Century Surface Warming Driven by Extratropical Cloud Feedbacks

NASA Astrophysics Data System (ADS)

Frey, W.; Maroon, E.; Pendergrass, A. G.; Kay, J. E.

2017-12-01

Equilibrium climate sensitivity (ECS), the warming in response to instantaneously doubled CO2, has long been used to compare climate models. In many models, ECS is well correlated with warming produced by transient forcing experiments. Modifications to cloud phase at high latitudes in a state-of-the-art climate model, the Community Earth System Model (CESM), produce a large increase in ECS (1.5 K) via extratropical cloud feedbacks. However, only a small surface warming increase occurs in a realistic 21st century simulation including a full-depth dynamic ocean and the "business as usual" RCP8.5 emissions scenario. In fact, the increase in surface warming is only barely above the internal variability-generated range in the CESM Large Ensemble. The small change in 21st century warming is attributed to subpolar ocean heat uptake in both hemispheres. In the Southern Ocean, the mean-state circulation takes up heat while in the North Atlantic a slowdown in circulation acts as a feedback to slow surface warming. These results show the importance of subpolar ocean heat uptake in controlling the pace of warming and demonstrate that ECS cannot be used to reliably infer transient warming when it is driven by extratropical feedbacks.

Do Southern Ocean Cloud Feedbacks Matter for 21st Century Warming?

NASA Astrophysics Data System (ADS)

Frey, W. R.; Maroon, E. A.; Pendergrass, A. G.; Kay, J. E.

2017-12-01

Cloud phase improvements in a state-of-the-art climate model produce a large 1.5 K increase in equilibrium climate sensitivity (ECS, the surface warming in response to instantaneously doubled CO2) via extratropical shortwave cloud feedbacks. Here we show that the same model improvements produce only a small surface warming increase in a realistic 21st century emissions scenario. The small 21st century warming increase is attributed to extratropical ocean heat uptake. Southern Ocean mean-state circulation takes up heat while a slowdown in North Atlantic circulation acts as a feedback to slow surface warming. Persistent heat uptake by extratropical oceans implies that extratropical cloud biases may not be as important to 21st century warming as biases in other regions. Observational constraints on cloud phase and shortwave radiation that produce a large ECS increase do not imply large changes in 21st century warming.

The rising greenhouse effect: experiments and observations in and around the Alps

NASA Astrophysics Data System (ADS)

Philipona, R.

2010-09-01

The rapid temperature increase of more than 1°C in central Europe over the last three decades is larger than expected from anthropogenic greenhouse warming. Surface radiation flux measurements in and around the Alps in fact confirm that not only thermal longwave radiation but also solar shortwave radiation increased since the 1980s. Surface energy budget analyses reveal the rising surface temperature to be well correlated with the radiative forcing, and also show an increase of the kinetic energy fluxes explaining the rise of atmospheric water vapor. Solar radiation mainly increased due to a strong decline of anthropogenic aerosols since mid of the 1980s. While anthropogenic aerosols were mainly accumulated in the boundary layer, this reduction let solar radiation to recover (solar brightening after several decades of solar dimming) mainly at low altitudes around the Alps. At high elevations in the Alps, solar forcing is much smaller and the respective temperature rise is also found to be smaller than in the lowlands. The fact that temperature increases less in the Alps than at low elevations is unexpected in the concept of greenhouse warming, but the radiation budget analyses clearly shows that in the plains solar forcing due to declining aerosols additionally increased surface temperature, whereas in the Alps temperature increased primarily due to greenhouse warming that is particularly manifested by a strong water vapor feedback.

Climate change threatens the world's marine protected areas

NASA Astrophysics Data System (ADS)

Bruno, John F.; Bates, Amanda E.; Cacciapaglia, Chris; Pike, Elizabeth P.; Amstrup, Steven C.; van Hooidonk, Ruben; Henson, Stephanie A.; Aronson, Richard B.

2018-06-01

Marine protected areas (MPAs) are a primary management tool for mitigating threats to marine biodiversity1,2. MPAs and the species they protect, however, are increasingly being impacted by climate change. Here we show that, despite local protections, the warming associated with continued business-as-usual emissions (RCP8.5)3 will likely result in further habitat and species losses throughout low-latitude and tropical MPAs4,5. With continued business-as-usual emissions, mean sea-surface temperatures within MPAs are projected to increase 0.035 °C per year and warm an additional 2.8 °C by 2100. Under these conditions, the time of emergence (the year when sea-surface temperature and oxygen concentration exceed natural variability) is mid-century in 42% of 309 no-take marine reserves. Moreover, projected warming rates and the existing `community thermal safety margin' (the inherent buffer against warming based on the thermal sensitivity of constituent species) both vary among ecoregions and with latitude. The community thermal safety margin will be exceeded by 2050 in the tropics and by 2150 for many higher latitude MPAs. Importantly, the spatial distribution of emergence is stressor-specific. Hence, rearranging MPAs to minimize exposure to one stressor could well increase exposure to another. Continued business-as-usual emissions will likely disrupt many marine ecosystems, reducing the benefits of MPAs.

CO2 condensation and the climate of early Mars.

PubMed

Kasting, J F

1991-01-01

A one-dimensional, radiative-convective climate model was used to reexamine the question of whether early Mars could have been kept warm by the greenhouse effect of a dense, CO2 atmosphere. The new model differs from previous models by considering the influence of CO2 clouds on the convective lapse rate and on the the planetary radiation budget. Condensation of CO2 decreases the lapse rate and, hence, reduces the magnitude of the greenhouse effect. This phenomenon becomes increasingly important at low solar luminosities and may preclude warm (0 degree C), globally averaged surface temperatures prior to approximately 2 billion years ago unless other greenhouse gases were present in addition to CO2 and H2O. Alternative mechanisms for warming early Mars and explaining channel formation are discussed.

Surface Heat Budgets and Sea Surface Temperature in the Pacific Warm Pool During TOGA COARE

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Zhao, Wenzhong; Chou, Ming-Dah

1998-01-01

The daily mean heat and momentum fluxes at the surface derived from the SSM/I and Japan's GMS radiance measurements are used to study the temporal and spatial variability of the surface energy budgets and their relationship to the sea surface temperature during the COARE intensive observing period (IOP). For the three time legs observed during the IOP, the retrieved surface fluxes compare reasonably well with those from the IMET buoy, RV Moana Wave, and RV Wecoma. The characteristics of surface heat and momentum fluxes are very different between the southern and northern warm pool. In the southern warm pool, the net surface heat flux is dominated by solar radiation which is, in turn, modulated by the two Madden-Julian oscillations. The surface winds are generally weak, leading to a shallow ocean mixed layer. The solar radiation penetrating through the bottom of the mixed layer is significant, and the change in the sea surface temperature during the IOP does not follow the net surface heat flux. In the northern warm pool, the northeasterly trade wind is strong and undergoes strong seasonal variation. The variation of the net surface heat flux is dominated by evaporation. The two westerly wind bursts associated with the Madden-Julian oscillations seem to have little effect on the net surface heat flux. The ocean mixed layer is deep, and the solar radiation penetrating through the bottom of the mixed layer is small. As opposed to the southern warm pool, the trend of the sea surface temperature in the northern warm pool during the IOP is in agreement with the variation of the net heat flux at the surface.

Large Scale Drivers for the Extreme Storm Season over the North Atlantic and the UK in Winter 2013-14

NASA Astrophysics Data System (ADS)

Wild, Simon; Befort, Daniel J.; Leckebusch, Gregor C.

2016-04-01

The British Isles experienced exceptional stormy and rainy weather conditions in winter 2013-2014 while large parts of central North America recorded near record minimum surface temperatures values. Potential drivers for these cold conditions include increasingly warm surface waters of the tropical west Pacific. It has been suggested these increasing sea surface temperatures could also be the cause for extreme weather over the Europe, particularly the UK. Testing this hypothesis, we investigate mechanisms linking the tropical west Pacific and European wind storm activity. We will firstly analyse anomaly patterns along such a potential link in winter 2013-14. Secondly, we will investigate whether these identified anomaly patterns show a strong interannual relationship in the recent past. Our results, using primarily ERA-Interim Reanalysis from 1979 to 2014, show an absolute maximum of wind storm frequency over the northeast Atlantic and the British Isles in winter 2013-14. We also find absolute minimum surface temperatures in central North America and increased convective activity over the tropical west Pacific in the same season. The winter 2013-14 was additionally characterized by anomalous warm sea surface temperatures over the subtropical northwest Atlantic. Although the interannual variability of wind storms in the northeast Atlantic and surface temperatures in North America are significantly anti-correlated, we cannot directly relate wind storm frequency with tropical west Pacific anomalies. We thus conclude that the conditions over the Pacific in winter 2013-14 were favourable but not sufficient to explain the record number of wind storms in this season. Instead, we suggest that warm north Atlantic sea surface temperature anomalies in combination with cold surface temperatures over North America played a more important role for generating higher wind storm counts over the northeast Atlantic and the UK.

An assessment of warm fog: Nucleation, control, and recommended research

NASA Technical Reports Server (NTRS)

Corrin, M. L.; Connell, J. R.; Gero, A. J.

1974-01-01

A state-of-the-art survey is given of warm fog research which has been performed up to, and including, 1974. Topics covered are nucleation, growth, coalescence, fog structures and visibility, effects of surface films, drop size spectrum, optical properties, instrumentation, liquid water content, condensation nuclei. Included is a summary of all reported fog modification experiments. Additional data is provided on air flow, turbulence, a summary of recommendations on instruments to be developed for determining turbulence, air flow, etc., as well as recommendations of various fog research tasks which should be performed for a better understanding of fog microphysics.

Local atmospheric response to warm mesoscale ocean eddies in the Kuroshio-Oyashio Confluence region.

PubMed

Sugimoto, Shusaku; Aono, Kenji; Fukui, Shin

2017-09-19

In the extratropical regions, surface winds enhance upward heat release from the ocean to atmosphere, resulting in cold surface ocean: surface ocean temperature is negatively correlated with upward heat flux. However, in the western boundary currents and eddy-rich regions, the warmer surface waters compared to surrounding waters enhance upward heat release-a positive correlation between upward heat release and surface ocean temperature, implying that the ocean drives the atmosphere. The atmospheric response to warm mesoscale ocean eddies with a horizontal extent of a few hundred kilometers remains unclear because of a lack of observations. By conducting regional atmospheric model experiments, we show that, in the Kuroshio-Oyashio Confluence region, wintertime warm eddies heat the marine atmospheric boundary layer (MABL), and accelerate westerly winds in the near-surface atmosphere via the vertical mixing effect, leading to wind convergence around the eastern edge of eddies. The warm-eddy-induced convergence forms local ascending motion where convective precipitation is enhanced, providing diabatic heating to the atmosphere above MABL. Our results indicate that warm eddies affect not only near-surface atmosphere but also free atmosphere, and possibly synoptic atmospheric variability. A detailed understanding of warm eddy-atmosphere interaction is necessary to improve in weather and climate projections.

Responses of ecosystem CO 2 fluxes to short-term experimental warming and nitrogen enrichment in an Alpine meadow, northern Tibet Plateau.

PubMed

Zong, Ning; Shi, Peili; Jiang, Jing; Song, Minghua; Xiong, Dingpeng; Ma, Weiling; Fu, Gang; Zhang, Xianzhou; Shen, Zhenxi

2013-01-01

Over the past decades, the Tibetan Plateau has experienced pronounced warming, yet the extent to which warming will affect alpine ecosystems depends on how warming interacts with other influential global change factors, such as nitrogen (N) deposition. A long-term warming and N manipulation experiment was established to investigate the interactive effects of warming and N deposition on alpine meadow. Open-top chambers were used to simulate warming. N addition, warming, N addition × warming, and a control were set up. In OTCs, daytime air and soil temperature were warmed by 2.0°C and 1.6°C above ambient conditions, but soil moisture was decreased by 4.95 m(3) m(-3). N addition enhanced ecosystem respiration (Reco); nevertheless, warming significantly decreased Reco. The decline of Reco resulting from warming was cancelled out by N addition in late growing season. Our results suggested that N addition enhanced Reco by increasing soil N availability and plant production, whereas warming decreased Reco through lowering soil moisture, soil N supply potential, and suppression of plant activity. Furthermore, season-specific responses of Reco indicated that warming and N deposition caused by future global change may have complicated influence on carbon cycles in alpine ecosystems.

Responses of Ecosystem CO2 Fluxes to Short-Term Experimental Warming and Nitrogen Enrichment in an Alpine Meadow, Northern Tibet Plateau

PubMed Central

Shi, Peili; Jiang, Jing; Song, Minghua; Xiong, Dingpeng; Ma, Weiling; Fu, Gang; Zhang, Xianzhou; Shen, Zhenxi

2013-01-01

Over the past decades, the Tibetan Plateau has experienced pronounced warming, yet the extent to which warming will affect alpine ecosystems depends on how warming interacts with other influential global change factors, such as nitrogen (N) deposition. A long-term warming and N manipulation experiment was established to investigate the interactive effects of warming and N deposition on alpine meadow. Open-top chambers were used to simulate warming. N addition, warming, N addition × warming, and a control were set up. In OTCs, daytime air and soil temperature were warmed by 2.0°C and 1.6°C above ambient conditions, but soil moisture was decreased by 4.95 m3 m−3. N addition enhanced ecosystem respiration (Reco); nevertheless, warming significantly decreased Reco. The decline of Reco resulting from warming was cancelled out by N addition in late growing season. Our results suggested that N addition enhanced Reco by increasing soil N availability and plant production, whereas warming decreased Reco through lowering soil moisture, soil N supply potential, and suppression of plant activity. Furthermore, season-specific responses of Reco indicated that warming and N deposition caused by future global change may have complicated influence on carbon cycles in alpine ecosystems. PMID:24459432

Global Ocean Circulation During Cretaceous Time

NASA Astrophysics Data System (ADS)

Haupt, B. J.; Seidov, D.

2001-12-01

Present--day global thermohaline ocean circulation (TOC) is usually associated with high--latitude deep-water formation due to surface cooling. In this understanding of the TOC driven by the deep--water production, the warm deep ocean during Mesozoic--Cenozoic time is a challenge. It may be questioned whether warm deep--ocean water, which is direct geologic evidence, does reflect warm polar surface--ocean regions. For the warm Cretaceous, it is difficult to maintain strong poleward heat transport in the case of reduced oceanic thermal contrasts. Usually, atmospheric feedbacks, in conjunction with the increase of atmospheric concentrations of greenhouse gases, are employed in order to explain the warm equable Cretaceous--Eocene climate. However, there is no feasible physical mechanism that could maintain warm subpolar surface oceans in both hemispheres, an assumption often used in atmospheric modeling. Our numerical experiments indicate that having a relatively cool but saltier high--latitude sea surface in at least one hemisphere is sufficient for driving a strong meridional overturning. Thus freshwater impacts in the high latitudes may be responsible for a vigorous conveyor capable of maintaining sufficient poleward oceanic heat transport needed to keep the polar oceans ice--free. These results imply that evaporation-precipitation patterns during warm climates are especially important climatic factors that can redistribute freshwater to create hemispheric asymmetry of sea surface conditions capable of generating a sufficiently strong TOC, otherwise impossible in warm climates.

Enhanced seasonal forecast skill following stratospheric sudden warmings

NASA Astrophysics Data System (ADS)

Sigmond, M.; Scinocca, J. F.; Kharin, V. V.; Shepherd, T. G.

2013-02-01

Advances in seasonal forecasting have brought widespread socio-economic benefits. However, seasonal forecast skill in the extratropics is relatively modest, prompting the seasonal forecasting community to search for additional sources of predictability. For over a decade it has been suggested that knowledge of the state of the stratosphere can act as a source of enhanced seasonal predictability; long-lived circulation anomalies in the lower stratosphere that follow stratospheric sudden warmings are associated with circulation anomalies in the troposphere that can last up to two months. Here, we show by performing retrospective ensemble model forecasts that such enhanced predictability can be realized in a dynamical seasonal forecast system with a good representation of the stratosphere. When initialized at the onset date of stratospheric sudden warmings, the model forecasts faithfully reproduce the observed mean tropospheric conditions in the months following the stratospheric sudden warmings. Compared with an equivalent set of forecasts that are not initialized during stratospheric sudden warmings, we document enhanced forecast skill for atmospheric circulation patterns, surface temperatures over northern Russia and eastern Canada and North Atlantic precipitation. We suggest that seasonal forecast systems initialized during stratospheric sudden warmings are likely to yield significantly greater forecast skill in some regions.

Quantifying the Negative Feedback of Vegetation to Greenhouse Warming: A Modeling Approach

NASA Technical Reports Server (NTRS)

Bounous, L.; Hall, F. G.; Sellers, P. J.; Kumar, A.; Collatz, G. J.; Tucker, C. J.; Imhoff, M. L.

2010-01-01

Several climate models indicate that in a 2 x CO2 environment, temperature and precipitation would increase and runoff would increase faster than precipitation. These models, however, did not allow the vegetation to increase its leaf density as a response to the physiological effects of increased CO2 and consequent changes in climate. Other assessments included these interactions but did not account for the vegetation down-regulation to reduce plant's photosynthetic activity and as such resulted in a weak vegetation negative response. When we combine these interactions in climate simulations with 2 x CO2, the associated increase in precipitation contributes primarily to increase evapotranspiration rather than surface runoff, consistent with observations, and results in an additional cooling effect not fully accounted for in previous simulations with elevated CO2. By accelerating the water cycle, this feedback slows but does not alleviate the projected warming, reducing the land surface warming by 0.6 C. Compared to previous studies, these results imply that long term negative feedback from CO2-induced increases in vegetation density could reduce temperature following a stabilization of CO2 concentration.

Warming and Nitrogen Addition Increase Litter Decomposition in a Temperate Meadow Ecosystem

PubMed Central

Gong, Shiwei; Guo, Rui; Zhang, Tao; Guo, Jixun

2015-01-01

Background Litter decomposition greatly influences soil structure, nutrient content and carbon sequestration, but how litter decomposition is affected by climate change is still not well understood. Methodology/Principal Findings A field experiment with increased temperature and nitrogen (N) addition was established in April 2007 to examine the effects of experimental warming, N addition and their interaction on litter decomposition in a temperate meadow steppe in northeastern China. Warming, N addition and warming plus N addition reduced the residual mass of L. chinensis litter by 3.78%, 7.51% and 4.53%, respectively, in 2008 and 2009, and by 4.73%, 24.08% and 16.1%, respectively, in 2010. Warming, N addition and warming plus N addition had no effect on the decomposition of P. communis litter in 2008 or 2009, but reduced the residual litter mass by 5.58%, 15.53% and 5.17%, respectively, in 2010. Warming and N addition reduced the cellulose percentage of L. chinensis and P. communis, specifically in 2010. The lignin percentage of L. chinensis and P. communis was reduced by warming but increased by N addition. The C, N and P contents of L. chinensis and P. communis litter increased with time. Warming and N addition reduced the C content and C:N ratios of L. chinensisand P. communis litter, but increased the N and P contents. Significant interactive effects of warming and N addition on litter decomposition were observed (P<0.01). Conclusion/Significance The litter decomposition rate was highly correlated with soil temperature, soil water content and litter quality. Warming and N addition significantly impacted the litter decomposition rate in the Songnen meadow ecosystem, and the effects of warming and N addition on litter decomposition were also influenced by the quality of litter. These results highlight how climate change could alter grassland ecosystem carbon, nitrogen and phosphorus contents in soil by influencing litter decomposition. PMID:25774776

Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

PubMed Central

Tokinaga, Hiroki; Xie, Shang-Ping; Mukougawa, Hitoshi

2017-01-01

With amplified warming and record sea ice loss, the Arctic is the canary of global warming. The historical Arctic warming is poorly understood, limiting our confidence in model projections. Specifically, Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing. Here, we show that the concurrent phase shift of Pacific and Atlantic interdecadal variability modes is the major driver for the rapid early 20th-century Arctic warming. Atmospheric model simulations successfully reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early 20th-century Arctic warming is associated with positive SST anomalies over the tropical and North Atlantic and a Pacific SST pattern reminiscent of the positive phase of the Pacific decadal oscillation. Atmospheric circulation changes are important for the early 20th-century Arctic warming. The equatorial Pacific warming deepens the Aleutian low, advecting warm air into the North American Arctic. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. Coupled ocean–atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, negative-to-positive phase shift of the Pacific and Atlantic interdecadal modes. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region. PMID:28559341

An increase in aerosol burden due to the land-sea warming contrast

NASA Astrophysics Data System (ADS)

Hassan, T.; Allen, R.; Randles, C. A.

2017-12-01

Climate models simulate an increase in most aerosol species in response to warming, particularly over the tropics and Northern Hemisphere midlatitudes. This increase in aerosol burden is related to a decrease in wet removal, primarily due to reduced large-scale precipitation. Here, we show that the increase in aerosol burden, and the decrease in large-scale precipitation, is related to a robust climate change phenomenon—the land/sea warming contrast. Idealized simulations with two state of the art climate models, the National Center for Atmospheric Research Community Atmosphere Model version 5 (NCAR CAM5) and the Geophysical Fluid Dynamics Laboratory Atmospheric Model 3 (GFDL AM3), show that muting the land-sea warming contrast negates the increase in aerosol burden under warming. This is related to smaller decreases in near-surface relative humidity over land, and in turn, smaller decreases in large-scale precipitation over land—especially in the NH midlatitudes. Furthermore, additional idealized simulations with an enhanced land/sea warming contrast lead to the opposite result—larger decreases in relative humidity over land, larger decreases in large-scale precipitation, and larger increases in aerosol burden. Our results, which relate the increase in aerosol burden to the robust climate projection of enhanced land warming, adds confidence that a warmer world will be associated with a larger aerosol burden.

Mechanisms of elevation-dependent warming over complex terrain in high-resolution simulations of regional climate change

NASA Astrophysics Data System (ADS)

Minder, J. R.; Letcher, T.; Liu, C.

2016-12-01

Numerous observational and modeling studies have suggested that over mountainous terrain certain elevations can experience systematically enhanced rates of near-surface climate warming relative to the surrounding region, a phenomenon referred to as elevation-dependent warming (EDW). In many of these studies high-elevation locations were found to experience the fastest warming rates. A variety of physical mechanisms for EDW have been proposed but there is no consensus as to the dominant cause. We examine EDW in regional climate model (RCM) simulations with very high horizontal resolution (4-km horizontal grid). The simulation domain centers on the Rocky Mountains and intermountain west of the United States. Climate change simulations are conducted using the "pseudo global warming" framework to focus on the regional response to large-scale thermodynamic and radiative climate changes representative of mid-century anthropogenic global climate change. Substantial EDW is found in these simulations. Warming varies with elevation by up to 1°C depending on the season considered. The structure of EDW is only weakly sensitive to variations in horizontal grid spacing ranging from 4 to 36 km. The snow-albedo feedback (SAF) plays a major role in causing the simulated EDW. The elevation band of maximum warming varies seasonally, mostly following the margin of the seasonal snowpack where snow cover and albedo reductions are maximized under climate warming. Additional simulations where the SAF is artificially suppressed demonstrate that EDW variations of up to 0.6°C can be attributed to the SAF. Simulations with a suppressed SAF still exhibit EDW variations up to 0.8°C that must be explained by other mechanisms. This remaining EDW shows a near linear increase in warming with elevation in most months and does not appear to be inherited from the profile of large-scale free-tropospheric warming. Simple theoretical calculations suggest that the non-linear dependence of surface emission on temperature offers one promising mechanism. The role of water vapor and cloud feedbacks are also considered as alternative mechanisms.

Spring snow albedo feedback in daily data over Russia: Comparing in-situ measurements with reanalysis products.

NASA Astrophysics Data System (ADS)

Wegmann, M.; Zolina, O.; Jacobi, H. W.

2016-12-01

Global warming is enhanced at high northern latitudes where the Arctic surface air temperature has risen at twice the rate of the global average in recent decades - a feature called Arctic amplification. This recent Arctic warming signal likely results from several factors such as the albedo feedback due to a diminishing cryosphere, enhanced poleward atmospheric and oceanic heat transport, and changes in humidity. Surface albedo feedback is stating that the additional amount of shortwave radiation at the top of the atmosphere decreases with decreasing surface albedo whereas surface air temperature increases with decreasing surface albedo. It is considered a positive feedback in that an initial warming perturbation than kicks off a strengthening warming. Looking at the Northern Hemisphere with its large landmasses, snow albedo feedback is especially strong since most of these landmasses experience snow cover during boreal wintertime. Unfortunately, so far there remains a lack of reliable observational data over large parts of the cryosphere. Satellite products cover large parts of the NH, however lack high temporal resolution and have problems with large solar zenith angles as well as over complex terrain (eg. Wang et al. 2014). Our analysis focuses at the Russian territory where we utilize in-situ radiation and snow depth measurements. We found 50 stations which measure both variables on a daily basis for the period 2000-2013. Since Hall (2004) found that 50% of the notal NH snow albedo feedback caused by global warming occurs during NH spring, we focus on the transition period of March to June (MAMJ). Thackeray & Fletcher 2006 compared albedo feedback processes CMIP3 and CMIP5 model families and found while the models represent the feedback process accurately, there are still inherent biases and outdated parameterizations. Therefore we use the daily observations and state of the art reanalysis products to 1) evaluate reanalysis and model products in respect to radiation properties, 2) investigate snow albedo feedbacks on a daily scale during spring and 3) to suggest climate change signals over Russia in albedo feedback between 2000 - 2013 based on in-situ measurements.

Revisiting the Cause of the 1989-2009 Arctic Surface Warming Using the Surface Energy Budget: Downward Infrared Radiation Dominates the Surface Fluxes

NASA Astrophysics Data System (ADS)

Lee, Sukyoung; Gong, Tingting; Feldstein, Steven B.; Screen, James A.; Simmonds, Ian

2017-10-01

The Arctic has been warming faster than elsewhere, especially during the cold season. According to the leading theory, ice-albedo feedback warms the Arctic Ocean during the summer, and the heat gained by the ocean is released during the winter, causing the cold-season warming. Screen and Simmonds (2010; SS10) concluded that the theory is correct by comparing trend patterns in surface air temperature (SAT), surface turbulence heat flux (HF), and net surface infrared radiation (IR). However, in this comparison, downward IR is more appropriate to use. By analyzing the same data used in SS10 using the surface energy budget, it is shown here that over most of the Arctic the skin temperature trend, which closely resembles the SAT trend, is largely accounted for by the downward IR, not the HF, trend.

The tropical Pacific as a key pacemaker of the variable rates of global warming

NASA Astrophysics Data System (ADS)

Kosaka, Yu; Xie, Shang-Ping

2016-09-01

Global mean surface temperature change over the past 120 years resembles a rising staircase: the overall warming trend was interrupted by the mid-twentieth-century big hiatus and the warming slowdown since about 1998. The Interdecadal Pacific Oscillation has been implicated in modulations of global mean surface temperatures, but which part of the mode drives the variability in warming rates is unclear. Here we present a successful simulation of the global warming staircase since 1900 with a global ocean-atmosphere coupled model where tropical Pacific sea surface temperatures are forced to follow the observed evolution. Without prescribed tropical Pacific variability, the same model, on average, produces a continual warming trend that accelerates after the 1960s. We identify four events where the tropical Pacific decadal cooling markedly slowed down the warming trend. Matching the observed spatial and seasonal fingerprints we identify the tropical Pacific as a key pacemaker of the warming staircase, with radiative forcing driving the overall warming trend. Specifically, tropical Pacific variability amplifies the first warming epoch of the 1910s-1940s and determines the timing when the big hiatus starts and ends. Our method of removing internal variability from the observed record can be used for real-time monitoring of anthropogenic warming.

Independent effects of warming and nitrogen addition on plant phenology in the Inner Mongolian steppe.

PubMed

Xia, Jianyang; Wan, Shiqiang

2013-06-01

Phenology is one of most sensitive traits of plants in response to regional climate warming. Better understanding of the interactive effects between warming and other environmental change factors, such as increasing atmosphere nitrogen (N) deposition, is critical for projection of future plant phenology. A 4-year field experiment manipulating temperature and N has been conducted in a temperate steppe in northern China. Phenology, including flowering and fruiting date as well as reproductive duration, of eight plant species was monitored and calculated from 2006 to 2009. Across all the species and years, warming significantly advanced flowering and fruiting time by 0·64 and 0·72 d per season, respectively, which were mainly driven by the earliest species (Potentilla acaulis). Although N addition showed no impact on phenological times across the eight species, it significantly delayed flowering time of Heteropappus altaicus and fruiting time of Agropyron cristatum. The responses of flowering and fruiting times to warming or N addition are coupled, leading to no response of reproductive duration to warming or N addition for most species. Warming shortened reproductive duration of Potentilla bifurca but extended that of Allium bidentatum, whereas N addition shortened that of A. bidentatum. No interactive effect between warming and N addition was found on any phenological event. Such additive effects could be ascribed to the species-specific responses of plant phenology to warming and N addition. The results suggest that the warming response of plant phenology is larger in earlier than later flowering species in temperate grassland systems. The effects of warming and N addition on plant phenology are independent of each other. These findings can help to better understand and predict the response of plant phenology to climate warming concurrent with other global change driving factors.

Modeling the Warming Impact of Urban Land Expansion on Hot Weather Using the Weather Research and Forecasting Model: A Case Study of Beijing, China

NASA Astrophysics Data System (ADS)

Liu, Xiaojuan; Tian, Guangjin; Feng, Jinming; Ma, Bingran; Wang, Jun; Kong, Lingqiang

2018-06-01

The impacts of three periods of urban land expansion during 1990-2010 on near-surface air temperature in summer in Beijing were simulated in this study, and then the interrelation between heat waves and urban warming was assessed. We ran the sensitivity tests using the mesoscaleWeather Research and Forecasting model coupled with a single urban canopy model, as well as high-resolution land cover data. The warming area expanded approximately at the same scale as the urban land expansion. The average regional warming induced by urban expansion increased but the warming speed declined slightly during 2000-2010. The smallest warming occurred at noon and then increased gradually in the afternoon before peaking at around 2000 LST—the time of sunset. In the daytime, urban warming was primarily caused by the decrease in latent heat flux at the urban surface. Urbanization led to more ground heat flux during the day and then more release at night, which resulted in nocturnal warming. Urban warming at night was higher than that in the day, although the nighttime increment in sensible heat flux was smaller. This was because the shallower planetary boundary layer at night reduced the release efficiency of near-surface heat. The simulated results also suggested that heat waves or high temperature weather enhanced urban warming intensity at night. Heat waves caused more heat to be stored in the surface during the day, greater heat released at night, and thus higher nighttime warming. Our results demonstrate a positive feedback effect between urban warming and heat waves in urban areas.

Putting oxygen and temperature thresholds of marine animals in context of environmental change in coastal seas: a regional perspective for the Scotian Shelf and Gulf of St. Lawrence

NASA Astrophysics Data System (ADS)

Brennan, Catherine E.; Blanchard, Hannah; Fennel, Katja

2014-05-01

We surveyed the literature in order to compile reported oxygen, temperature, salinity and depth preferences and thresholds of important marine species found in the Gulf of St. Lawrence and the Scotian Shelf regions of the northwest North Atlantic. We determined species importance based on the existence of a commercial fishery, a threatened or at risk status, or by meeting the following criteria: bycatch, baitfish, invasive, vagrant, important for ecosystem energy transfer, and predators and prey of the above species. Using the dataset compiled for the 53 regional fishes and macroinvertebrates, we rank species (including for different lifestages) by their maximum thermal limit, as well as by the lowest oxygen concentration tolerated before negative impacts (e.g. physiological stress), 50% mortality or 100% mortality are experienced. Additionally, we compare these thresholds to observed marine deoxygenation trends at multiple sites, and observed surface warming trends. This results in an assessment of which regional species are most vulnerable to future warming and oxygen depletion, and a first-order estimate of the consequences of thermal and oxygen stress on a highly productive marine shelf. If regional multi-decadal oxygen and temperature trends continue through the 21st century, many species will lose favorable oxygen conditions, experience oxygen-stress, or disappear due to insufficient oxygen. Future warming can additionally displace vulnerable species, though we note that large natural variability in environmental conditions may amplify or dampen the effects of anthropogenic surface warming trends. This dataset may be combined with regional ocean model predictions to map future species distributions.

Dynamical Core in Atmospheric Model Does Matter in the Simulation of Arctic Climate

NASA Astrophysics Data System (ADS)

Jun, Sang-Yoon; Choi, Suk-Jin; Kim, Baek-Min

2018-03-01

Climate models using different dynamical cores can simulate significantly different winter Arctic climates even if equipped with virtually the same physics schemes. Current climate simulated by the global climate model using cubed-sphere grid with spectral element method (SE core) exhibited significantly warmer Arctic surface air temperature compared to that using latitude-longitude grid with finite volume method core. Compared to the finite volume method core, SE core simulated additional adiabatic warming in the Arctic lower atmosphere, and this was consistent with the eddy-forced secondary circulation. Downward longwave radiation further enhanced Arctic near-surface warming with a higher surface air temperature of about 1.9 K. Furthermore, in the atmospheric response to the reduced sea ice conditions with the same physical settings, only the SE core showed a robust cooling response over North America. We emphasize that special attention is needed in selecting the dynamical core of climate models in the simulation of the Arctic climate and associated teleconnection patterns.

Enhanced wintertime greenhouse effect reinforcing Arctic amplification and initial sea-ice melting.

PubMed

Cao, Yunfeng; Liang, Shunlin; Chen, Xiaona; He, Tao; Wang, Dongdong; Cheng, Xiao

2017-08-16

The speeds of both Arctic surface warming and sea-ice shrinking have accelerated over recent decades. However, the causes of this unprecedented phenomenon remain unclear and are subjects of considerable debate. In this study, we report strong observational evidence, for the first time from long-term (1984-2014) spatially complete satellite records, that increased cloudiness and atmospheric water vapor in winter and spring have caused an extraordinary downward longwave radiative flux to the ice surface, which may then amplify the Arctic wintertime ice-surface warming. In addition, we also provide observed evidence that it is quite likely the enhancement of the wintertime greenhouse effect caused by water vapor and cloudiness has advanced the time of onset of ice melting in mid-May through inhibiting sea-ice refreezing in the winter and accelerating the pre-melting process in the spring, and in turn triggered the positive sea-ice albedo feedback process and accelerated the sea ice melting in the summer.

Ice Core Records of West Greenland Melt and Climate Forcing

NASA Astrophysics Data System (ADS)

Graeter, K. A.; Osterberg, E. C.; Ferris, D. G.; Hawley, R. L.; Marshall, H. P.; Lewis, G.; Meehan, T.; McCarthy, F.; Overly, T.; Birkel, S. D.

2018-04-01

Remote sensing observations and climate models indicate that the Greenland Ice Sheet (GrIS) has been losing mass since the late 1990s, mostly due to enhanced surface melting from rising summer temperatures. However, in situ observational records of GrIS melt rates over recent decades are rare. Here we develop a record of frozen meltwater in the west GrIS percolation zone preserved in seven firn cores. Quantifying ice layer distribution as a melt feature percentage (MFP), we find significant increases in MFP in the southernmost five cores over the past 50 years to unprecedented modern levels (since 1550 CE). Annual to decadal changes in summer temperatures and MFP are closely tied to changes in Greenland summer blocking activity and North Atlantic sea surface temperatures since 1870. However, summer warming of 1.2°C since 1870-1900, in addition to warming attributable to recent sea surface temperature and blocking variability, is a critical driver of high modern MFP levels.

Potential causes of differences between ground and surface air temperature warming across different ecozones in Alberta, Canada

NASA Astrophysics Data System (ADS)

Majorowicz, Jacek A.; Skinner, Walter R.

1997-10-01

Analysis and modelling of temperature anomalies from 25 selected deep wells in Alberta show that the differences between GST (ground surface temperature) warming for the northern Boreal Forest ecozone and the combined Prairie Grassland ecozone and Aspen Parkland transition region to the south occur during the latter half of this century. This corresponds with recent changes in surface albedo resulting from permanent land development in the northern areas and also to increases in natural forest fires in the past 20 years. Differences between GST and SAT (surface air temperature) warming are much higher in the Boreal Forest ecozone than in the Prairie Grassland ecozone and Aspen Parkland transition region. Various hypotheses which could account for the existing differences between the GST and SAT warming in the different ecozones of Alberta, and western Canada in general, are tested. Analysis of existing data on soil temperature, hydrological piezometric surfaces, snowfall and moisture patterns, and land clearing and forest fires, indicate that large areas of Alberta, characterised by anomalous GST warming, have experienced widespread changes to the surface landscape in this century. It is postulated that this has resulted in a lower surface albedo with a subsequent increase in the absorption of solar energy. Heat flow modelling shows that, after climatic SAT warming, permanent clearing of the land is the most effective and likely cause of the observed changes in the GST warming. The greater GST warming in the Boreal Forest ecozone in the latter half of this century is related to landscape change due to land development and increasing forest fire activity. It appears to account for a portion of the observed SAT warming in this region through a positive feedback loop with the overlying air. The anthropogenic effect on regional climatic warming through 20th century land clearing and landscape alteration requires further study. In future, more accurate quantification of these various forcings will be necessary in order to distinguish between, and to detect, the variety of natural and anthropogenic influences and on climate.

The relationship between interannual and long-term cloud feedbacks

DOE PAGES

Zhou, Chen; Zelinka, Mark D.; Dessler, Andrew E.; ...

2015-12-11

The analyses of Coupled Model Intercomparison Project phase 5 simulations suggest that climate models with more positive cloud feedback in response to interannual climate fluctuations also have more positive cloud feedback in response to long-term global warming. Ensemble mean vertical profiles of cloud change in response to interannual and long-term surface warming are similar, and the ensemble mean cloud feedback is positive on both timescales. However, the average long-term cloud feedback is smaller than the interannual cloud feedback, likely due to differences in surface warming pattern on the two timescales. Low cloud cover (LCC) change in response to interannual andmore » long-term global surface warming is found to be well correlated across models and explains over half of the covariance between interannual and long-term cloud feedback. In conclusion, the intermodel correlation of LCC across timescales likely results from model-specific sensitivities of LCC to sea surface warming.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Chen; Zelinka, Mark D.; Dessler, Andrew E.

The analyses of Coupled Model Intercomparison Project phase 5 simulations suggest that climate models with more positive cloud feedback in response to interannual climate fluctuations also have more positive cloud feedback in response to long-term global warming. Ensemble mean vertical profiles of cloud change in response to interannual and long-term surface warming are similar, and the ensemble mean cloud feedback is positive on both timescales. However, the average long-term cloud feedback is smaller than the interannual cloud feedback, likely due to differences in surface warming pattern on the two timescales. Low cloud cover (LCC) change in response to interannual andmore » long-term global surface warming is found to be well correlated across models and explains over half of the covariance between interannual and long-term cloud feedback. In conclusion, the intermodel correlation of LCC across timescales likely results from model-specific sensitivities of LCC to sea surface warming.« less

Small change, big difference: Sea surface temperature distributions for tropical coral reef ecosystems, 1950-2011

NASA Astrophysics Data System (ADS)

Lough, J. M.

2012-09-01

Changes in tropical sea surface temperature (SST) are examined over the period 1950-2011 during which global average temperature warmed by 0.4°C. Average tropical SST is warming about 70% of the global average rate. Spatially, significant warming between the two time periods, 1950-1980 and 1981-2011, has occurred across 65% of the tropical oceans. Coral reef ecosystems occupy 10% of the tropical oceans, typically in regions of warmer (+1.8°C) and less variable SST (80% of months within 3.3°C range) compared to non-reef areas (80% of months within 7.0°C range). SST is a primary controlling factor of coral reef distribution and coral reef organisms have already shown their sensitivity to the relatively small amount of warming observed so far through, for example, more frequent coral bleaching events and outbreaks of coral disease. Experimental evidence is also emerging of possible thermal thresholds in the range 30°C-32°C for some physiological processes of coral reef organisms. Relatively small changes in SST have already resulted in quite large differences in SST distribution with a maximum ‘hot spot’ of change in the near-equatorial Indo-Pacific which encompasses both the Indo-Pacific warm pools and the center of coral reef biodiversity. Identification of this hot spot of SST change is not new but this study highlights its significance with respect to tropical coral reef ecosystems. Given the modest amount of warming to date, changes in SST distribution are of particular concern for coral reefs given additional local anthropogenic stresses on many reefs and ongoing ocean acidification likely to increasingly compromise coral reef processes.

Foehn and temperature-based melt patterns over the Larsen C Ice Shelf as simulated by the MAR regional climate model

NASA Astrophysics Data System (ADS)

Datta, R.; Tedesco, M.; Agosta, C.; Fettweis, X.; Kuipers Munneke, P.; van den Broeke, M. R.

2017-12-01

Surface melting has been implicated in the collapse of Antarctic Peninsula ice shelves, most dramatically in the Larsen A (1995) and Larsen B (2002) ice shelves. In July of this year, a rift in the remaining Larsen C ice shelf broke away one of the largest icebergs ever recorded. Ice-shelf retreat is likely related to strong atmospheric warming in this area, by means of hydrofracturing and possibly by the warming atmosphere itself. According the hydrofracture mechanism, meltwater produced during anomalously warm summers infiltrates and deepens pre-existent crevasses, leading to the eventual break-up of the ice shelf. In addition to region-wide warming, melting in the East Antarctic Peninsula can be caused by frequent intrusions of westerly foehn winds. The remaining Larsen C ice shelf, as well as glaciers previously feeding to the former Larsen B ice shelf, are therefore vulnerable to both (a) the atmospheric circulation patterns that influence foehn wind frequency and intensity and (b) regional interannual temperature trends. We discuss spatial patterns of meltwater production in the northeast basin of the Antarctic Peninsula as modeled by the Modèle Atmosphérique Régionale (MAR) at a 10km resolution between 2001 and 2014. The timeseries associated with these patterns are used to identify interannual changes in the frequency of foehn-induced melt, and compare foehn-induced melting to melt associated with regional warming. Melt occurrence in MAR is evaluated against multiple satellite datasets and near-surface automatic weather station data from three sites. Finally, we discuss the seasonal depth to which meltwater percolates into the snowpack (as modeled by MAR) because of the potential influence of meltwater on both warming and densification of the ice shelf.

Tropical Pacific variability as a key pacemaker of the global warming staircase

NASA Astrophysics Data System (ADS)

Kosaka, Y.; Xie, S. P.

2016-12-01

Global-mean surface temperature (GMST) has increased since the 19th century with notable interdecadal accelerations and slowdowns, forming the global-warming "staircase". The last step of this staircase is the surface warming slowdown since the late 1990s, for which the transition of the Interdecadal Pacific Oscillation (IPO) from a positive to negative state has been suggested as the leading mechanism. To examine the role of IPO in the entire warming staircase, a long pacemaker experiment is performed with a coupled climate model where tropical Pacific sea surface temperatures are forced to follow the observed evolution since the late 19th century. The pacemaker experiment successfully reproduces the staircase-like global warming remarkably well since 1900. Without the tropical Pacific effect, the same model produces a continual warming from the 1900s to the 1960 followed by rapid warming. The successful reproduction identifies the tropical Pacific decadal variability as a key pacemaker of the GMST staircase. We further propose a method to remove internal variability from observed GMST changes for real-time monitoring of anthropogenic warming.

Does the climate warming hiatus exist over the Tibetan Plateau?

PubMed

Duan, Anmin; Xiao, Zhixiang

2015-09-02

The surface air temperature change over the Tibetan Plateau is determined based on historical observations from 1980 to 2013. In contrast to the cooling trend in the rest of China, and the global warming hiatus post-1990s, an accelerated warming trend has appeared over the Tibetan Plateau during 1998-2013 (0.25 °C decade(-1)), compared with that during 1980-1997 (0.21 °C decade(-1)). Further results indicate that, to some degree, such an accelerated warming trend might be attributable to cloud-radiation feedback. The increased nocturnal cloud over the northern Tibetan Plateau would warm the nighttime temperature via enhanced atmospheric back-radiation, while the decreased daytime cloud over the southern Tibetan Plateau would induce the daytime sunshine duration to increase, resulting in surface air temperature warming. Meanwhile, the in situ surface wind speed has recovered gradually since 1998, and thus the energy concentration cannot explain the accelerated warming trend over the Tibetan Plateau after the 1990s. It is suggested that cloud-radiation feedback may play an important role in modulating the recent accelerated warming trend over the Tibetan Plateau.

Observational Evidence for Desert Amplification Using Multiple Satellite Datasets.

PubMed

Wei, Nan; Zhou, Liming; Dai, Yongjiu; Xia, Geng; Hua, Wenjian

2017-05-17

Desert amplification identified in recent studies has large uncertainties due to data paucity over remote deserts. Here we present observational evidence using multiple satellite-derived datasets that desert amplification is a real large-scale pattern of warming mode in near surface and low-tropospheric temperatures. Trend analyses of three long-term temperature products consistently confirm that near-surface warming is generally strongest over the driest climate regions and this spatial pattern of warming maximizes near the surface, gradually decays with height, and disappears in the upper troposphere. Short-term anomaly analyses show a strong spatial and temporal coupling of changes in temperatures, water vapor and downward longwave radiation (DLR), indicating that the large increase in DLR drives primarily near surface warming and is tightly associated with increasing water vapor over deserts. Atmospheric soundings of temperature and water vapor anomalies support the results of the long-term temperature trend analysis and suggest that desert amplification is due to comparable warming and moistening effects of the troposphere. Likely, desert amplification results from the strongest water vapor feedbacks near the surface over the driest deserts, where the air is very sensitive to changes in water vapor and thus efficient in enhancing the longwave greenhouse effect in a warming climate.

Global warming 2007. An update to global warming: the balance of evidence and its policy implications.

PubMed

Keller, Charles F

2007-03-09

In the four years since my original review (Keller[25]; hereafter referred to as CFK03), research has clarified and strengthened our understanding of how humans are warming the planet. So many of the details highlighted in the IPCC's Third Assessment Report[21] and in CFK03 have been resolved that I expect many to be a bit overwhelmed, and I hope that, by treating just the most significant aspects of the research, this update may provide a road map through the expected maze of new information. In particular, while most of CFK03 remains current, there are important items that have changed: Most notable is the resolution of the conundrum that mid-tropospheric warming did not seem to match surface warming. Both satellite and radiosonde (balloon-borne sensors) data reduction showed little warming in the middle troposphere (4-8 km altitude). In the CFK03 I discussed potential solutions to this problem, but at that time there was no clear resolution. This problem has now been solved, and the middle troposphere is seen to be warming apace with the surface. There have also been advances in determinations of temperatures over the past 1,000 years showing a cooler Little Ice Age (LIA) but essentially the same warming during medieval times (not as large as recent warming). The recent uproar over the so-called "hockey stick" temperature determination is much overblown since at least seven other groups have made relatively independent determinations of northern hemisphere temperatures over the same time period and derived essentially the same results. They differ on how cold the LIA was but essentially agree with the Mann's hockey stick result that the Medieval Warm Period was not as warm as the last 25 years. The question of the sun's influence on climate continues to generate controversy. It appears there is a growing consensus that, while the sun was a major factor in earlier temperature variations, it is incapable of having caused observed warming in the past quarter century or so. However, this conclusion is being challenged by differing interpretations of satellite observations of Total Solar Insolation (TSI). Different satellites give different estimates of TSI during the 1996-7 solar activity minimum. A recent study using the larger TSI satellite interpretation indicates a stronger role for the sun, and until there is agreement on TSI at solar minimum, we caution completely disregarding the sun as a significant factor in recent warming. Computer models continue to improve and, while they still do not do a satisfactory job of predicting regional changes, their simulations of global aspects of climate change and of individual forcings are increasingly reliable. In addition to these four areas, the past five years have seen advances in our understanding of many other aspects of climate change--from albedo changes due to land use to the dynamics of glacier movement. However, these more are of second order importance and will only be treated very briefly. The big news since CFK03 is the first of these, the collapse of the climate critics' last real bastion, namely that satellites and radiosondes show no significant warming in the past quarter century. Figuratively speaking, this was the center pole that held up the critics' entire "tent." Their argument was that, if there had been little warming in the past 25 years or so, then what warming was observed would have been within the range of natural variations with solar forcing as the major player. Further, the models would have been shown to be unreliable since they were predicting warming that was not happening. But now both satellite and in-situ radiosonde observations have been shown to corroborate both the surface observations of warming and the model predictions. Thus, while uncertainties still remain, we are now seeing a coherent picture in which past climate variations, solar and other forcings, model predictions and other indicators such as glacier recession all point to a human-induced warming that needs to be considered carefully. A final topic touched on briefly here is the new understanding of the phenomenon called "global dimming." Several sets of observations of the sun's total radiation at the surface have shown that there has been a reduction in sunlight reaching it. This has been related to the scattering of sunlight by aerosols and has led to a better quantification of the possibility that cleaning up our atmospheric pollution will lead to greater global warming. Adding all these advances together, there is a growing consensus that the 21st century will indeed see some 2 degrees C (3.5 degrees F) or more in additional warming. This is corroborated in the new IPCC Assessment, an early release of which is touched on very briefly here.

Influence of Sub-grid-Scale Isentropic Transports on McRAS Evaluations using ARM-CART SCM Datasets

NASA Technical Reports Server (NTRS)

Sud, Y. C.; Walker, G. K.; Tao, W. K.

2004-01-01

In GCM-physics evaluations with the currently available ARM-CART SCM datasets, McRAS produced very similar character of near surface errors of simulated temperature and humidity containing typically warm and moist biases near the surface and cold and dry biases aloft. We argued it must have a common cause presumably rooted in the model physics. Lack of vertical adjustment of horizontal transport was thought to be a plausible source. Clearly, debarring such a freedom would force the incoming air to diffuse into the grid-cell which would naturally bias the surface air to become warm and moist while the upper air becomes cold and dry, a characteristic feature of McRAS biases. Since, the errors were significantly larger in the two winter cases that contain potentially more intense episodes of cold and warm advective transports, it further reaffirmed our argument and provided additional motivation to introduce the corrections. When the horizontal advective transports were suitably modified to allow rising and/or sinking following isentropic pathways of subgrid scale motions, the outcome was to cool and dry (or warm and moisten) the lower (or upper) levels. Ever, crude approximations invoking such a correction reduced the temperature and humidity biases considerably. The tests were performed on all the available ARM-CART SCM cases with consistent outcome. With the isentropic corrections implemented through two different numerical approximations, virtually similar benefits were derived further confirming the robustness of our inferences. These results suggest the need for insentropic advective transport adjustment in a GCM due to subgrid scale motions.

Causes of irregularities in trends of global mean surface temperature since the late 19th century

PubMed Central

2018-01-01

The time series of monthly global mean surface temperature (GST) since 1891 is successfully reconstructed from known natural and anthropogenic forcing factors, including internal climate variability, using a multiple regression technique. Comparisons are made with the performance of 40 CMIP5 models in predicting GST. The relative contributions of the various forcing factors to GST changes vary in time, but most of the warming since 1891 is found to be attributable to the net influence of increasing greenhouse gases and anthropogenic aerosols. Separate statistically independent analyses are also carried out for three periods of GST slowdown (1896–1910, 1941–1975, and 1998–2013 and subperiods); two periods of strong warming (1911–1940 and 1976–1997) are also analyzed. A reduction in total incident solar radiation forcing played a significant cooling role over 2001–2010. The only serious disagreements between the reconstructions and observations occur during the Second World War, especially in the period 1944–1945, when observed near-worldwide sea surface temperatures (SSTs) may be significantly warm-biased. In contrast, reconstructions of near-worldwide SSTs were rather warmer than those observed between about 1907 and 1910. However, the generally high reconstruction accuracy shows that known external and internal forcing factors explain all the main variations in GST between 1891 and 2015, allowing for our current understanding of their uncertainties. Accordingly, no important additional factors are needed to explain the two main warming and three main slowdown periods during this epoch. PMID:29881771

Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect.

PubMed

Swann, Abigail L; Fung, Inez Y; Levis, Samuel; Bonan, Gordon B; Doney, Scott C

2010-01-26

Arctic climate is projected to change dramatically in the next 100 years and increases in temperature will likely lead to changes in the distribution and makeup of the Arctic biosphere. A largely deciduous ecosystem has been suggested as a possible landscape for future Arctic vegetation and is seen in paleo-records of warm times in the past. Here we use a global climate model with an interactive terrestrial biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is up to 1.5 times larger than the forcing due to albedo change from the forest. Furthermore, the greenhouse warming by additional water vapor melts sea-ice and triggers a positive feedback through changes in ocean albedo and evaporation. Land surface albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration of water vapor and feedbacks from the ocean and sea-ice.

Increasing occurrence of cold and warm extremes during the recent global warming slowdown.

PubMed

Johnson, Nathaniel C; Xie, Shang-Ping; Kosaka, Yu; Li, Xichen

2018-04-30

The recent levelling of global mean temperatures after the late 1990s, the so-called global warming hiatus or slowdown, ignited a surge of scientific interest into natural global mean surface temperature variability, observed temperature biases, and climate communication, but many questions remain about how these findings relate to variations in more societally relevant temperature extremes. Here we show that both summertime warm and wintertime cold extreme occurrences increased over land during the so-called hiatus period, and that these increases occurred for distinct reasons. The increase in cold extremes is associated with an atmospheric circulation pattern resembling the warm Arctic-cold continents pattern, whereas the increase in warm extremes is tied to a pattern of sea surface temperatures resembling the Atlantic Multidecadal Oscillation. These findings indicate that large-scale factors responsible for the most societally relevant temperature variations over continents are distinct from those of global mean surface temperature.

Red cell surface changes in cold agglutination

PubMed Central

Salsbury, A. J.; Clarke, J. A.; Shand, W. S.

1968-01-01

Surface changes in red blood cells undergoing cold agglutination have been investigated using the Cambridge Stereoscan electron microscope. On incubation of red cells with a cold agglutinin of anti-I specificity at 4°C, circular shadows on the red cell membrane developed within 2 min. At the same time the membrane showed a granularity and processes began to develop on the surface. These processes increased in length, the processes of contiguous cells became interlinked and agglutination was complete after incubation of 1 hr. On warming an agglutinated specimen, the process was reversed with separation of red cells and retraction of the finger-like processes to yield discrete red cells of normal appearance. The addition of heparin in vivo prevented agglutination but did not inhibit surface changes completely. Complement appeared to play no part in the production of cold agglutination due to these antibodies or in the reversal of agglutination by warming. The significance of the surface changes described in relation to previous information on the mechanism of agglutination, has been discussed. ImagesFig. 1Fig. 2Fig. 3Fig. 4Fig. 5Fig. 6Fig. 7Fig. 8Fig. 9Fig. 10Fig. 11 PMID:5655472

From global to regional and back again: common climate stressors of marine ecosystems relevant for adaptation across five ocean warming hotspots.

PubMed

Popova, Ekaterina; Yool, Andrew; Byfield, Valborg; Cochrane, Kevern; Coward, Andrew C; Salim, Shyam S; Gasalla, Maria A; Henson, Stephanie A; Hobday, Alistair J; Pecl, Gretta T; Sauer, Warwick H; Roberts, Michael J

2016-06-01

Ocean warming 'hotspots' are regions characterized by above-average temperature increases over recent years, for which there are significant consequences for both living marine resources and the societies that depend on them. As such, they represent early warning systems for understanding the impacts of marine climate change, and test-beds for developing adaptation options for coping with those impacts. Here, we examine five hotspots off the coasts of eastern Australia, South Africa, Madagascar, India and Brazil. These particular hotspots have underpinned a large international partnership that is working towards improving community adaptation by characterizing, assessing and projecting the likely future of coastal-marine food resources through the provision and sharing of knowledge. To inform this effort, we employ a high-resolution global ocean model forced by Representative Concentration Pathway 8.5 and simulated to year 2099. In addition to the sea surface temperature, we analyse projected stratification, nutrient supply, primary production, anthropogenic CO2 -driven ocean acidification, deoxygenation and ocean circulation. Our simulation finds that the temperature-defined hotspots studied here will continue to experience warming but, with the exception of eastern Australia, may not remain the fastest warming ocean areas over the next century as the strongest warming is projected to occur in the subpolar and polar areas of the Northern Hemisphere. Additionally, we find that recent rapid change in SST is not necessarily an indicator that these areas are also hotspots of the other climatic stressors examined. However, a consistent facet of the hotspots studied here is that they are all strongly influenced by ocean circulation, which has already shown changes in the recent past and is projected to undergo further strong change into the future. In addition to the fast warming, change in local ocean circulation represents a distinct feature of present and future climate change impacting marine ecosystems in these areas. © 2016 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.

Tracking ocean heat uptake during the surface warming hiatus

DOE PAGES

Liu, Wei; Xie, Shang -Ping; Lu, Jian

2016-03-30

Ocean heat uptake is observed to penetrate deep during the recent hiatus1,2,3 of global warming in the Atlantic and Southern Ocean. This has been suggested to indicate that the two regions are the driver of the surface warming hiatus4. We show that the deep heat penetration in the Atlantic and Southern Ocean is not unique to the hiatus but common to the past four decades including the 1970s-90s epoch of accelerated surface warming. Our analyses of a large ensemble simulation5 confirm the deep heat penetration in the Atlantic and Southern Ocean in ensemble members with or without surface warming hiatusmore » in the early 21th century. During the past four decades, the global ocean heat content (OHC) of upper 1500m is dominated by a warming trend, and the depth of anthropogenic heat penetration merely reflects the depth of the mean meridional overturning circulation in the basin. Furthermore, the heat penetration depth is not a valid basis to infer the hiatus mechanism.« less

Determination and impact of surface radiative processes for TOGA COARE

NASA Technical Reports Server (NTRS)

Curry, Judith A.; Ackerman, Thomas; Rossow, William B.; Webster, Peter J.

1991-01-01

Experiments using atmospheric general circulation models have shown that the atmospheric circulation is very sensitive to small changes in sea surface temperature in the tropical western Pacific Ocean warm pool region. The mutual sensitivity of the ocean and the atmosphere in the warm pool region places stringent requirements on models of the coupled ocean atmosphere system. At present, the situation is such that diagnostic studies using available data sets have been unable to balance the surface energy budget in the warm pool region to better than 50 to 80 W/sq m. The Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE) is an observation and modelling program that aims specifically at the elucidation of the physical process which determine the mean and transient state of the warm pool region and the manner in which the warm pool interacts with the global ocean and atmosphere. This project focuses on one very important aspect of the ocean atmosphere interface component of TOGA COARE, namely the temporal and spatial variability of surface radiative fluxes in the warm pool region.

Tracking ocean heat uptake during the surface warming hiatus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei; Xie, Shang -Ping; Lu, Jian

Ocean heat uptake is observed to penetrate deep during the recent hiatus1,2,3 of global warming in the Atlantic and Southern Ocean. This has been suggested to indicate that the two regions are the driver of the surface warming hiatus4. We show that the deep heat penetration in the Atlantic and Southern Ocean is not unique to the hiatus but common to the past four decades including the 1970s-90s epoch of accelerated surface warming. Our analyses of a large ensemble simulation5 confirm the deep heat penetration in the Atlantic and Southern Ocean in ensemble members with or without surface warming hiatusmore » in the early 21th century. During the past four decades, the global ocean heat content (OHC) of upper 1500m is dominated by a warming trend, and the depth of anthropogenic heat penetration merely reflects the depth of the mean meridional overturning circulation in the basin. Furthermore, the heat penetration depth is not a valid basis to infer the hiatus mechanism.« less

[Responses of plant community structure and species composition to warming and N addition in an alpine meadow, northern Tibetan Plateau, China].

PubMed

Zong, Ning; Chai, Xi; Shi, Pei Li; Jiang, Jing; Niu, Ben; Zhang, Xian Zhou; He, Yong Tao

2016-12-01

Global climate warming and increasing nitrogen (N) deposition, as controversial global environmental issues, may distinctly affect the functions and processes of terrestrial ecosystems. It has been reported that the Qinghai-Tibet Plateau has been experiencing significant warming in recent decades, especially in winter. Previous studies have mainly focused on the effects of warming all the year round; however, few studies have tested the effects of winter warming. To investigate the effects of winter warming and N addition on plant community structure and species composition of alpine meadow, long-term N addition and simulated warming experiment was conducted in alpine meadow from 2010 in Damxung, northern Tibet. The experiment consisted of three warming patterns: Year-round warming (YW), winter warming (WW) and control (NW), crossed respectively with five N gradients: 0, 10, 20, 40, 80 kg N·hm -2 ·a -1 . From 2012 to 2014, both warming and N addition significantly affected the total coverage of plant community. Specifically, YW significantly decreased the total coverage of plant community. Without N addition, WW remarkably reduced the vegetation coverage. However, with N addition, the total vegetation coverage gradually increased with the increase of N level. Warming and N addition had different effects on plants from different functional groups. Warming significantly reduced the plant coverage of grasses and sedges, while N addition significantly enhanced the plant coverage of grasses. Regression analyses showed that the total coverage of plant community was positively related to soil water content in vigorous growth stages, indicating that the decrease in soil water content resulted from warming during dry seasons might be the main reason for the decline of total community coverage. As soil moisture in semi-arid alpine meadow is mainly regulated by rainfalls, our results indicated that changes in spatial and temporal patterns of rainfalls under the future climate change scenarios would dramatically influence the vegetation coverage and species composition. Additionally, the effects of increasing atmospheric N deposition on vegetation community might also depend on the change of rainfall patterns.

Independent effects of warming and nitrogen addition on plant phenology in the Inner Mongolian steppe

PubMed Central

Xia, Jianyang; Wan, Shiqiang

2013-01-01

Background and Aims Phenology is one of most sensitive traits of plants in response to regional climate warming. Better understanding of the interactive effects between warming and other environmental change factors, such as increasing atmosphere nitrogen (N) deposition, is critical for projection of future plant phenology. Methods A 4-year field experiment manipulating temperature and N has been conducted in a temperate steppe in northern China. Phenology, including flowering and fruiting date as well as reproductive duration, of eight plant species was monitored and calculated from 2006 to 2009. Key Results Across all the species and years, warming significantly advanced flowering and fruiting time by 0·64 and 0·72 d per season, respectively, which were mainly driven by the earliest species (Potentilla acaulis). Although N addition showed no impact on phenological times across the eight species, it significantly delayed flowering time of Heteropappus altaicus and fruiting time of Agropyron cristatum. The responses of flowering and fruiting times to warming or N addition are coupled, leading to no response of reproductive duration to warming or N addition for most species. Warming shortened reproductive duration of Potentilla bifurca but extended that of Allium bidentatum, whereas N addition shortened that of A. bidentatum. No interactive effect between warming and N addition was found on any phenological event. Such additive effects could be ascribed to the species-specific responses of plant phenology to warming and N addition. Conclusions The results suggest that the warming response of plant phenology is larger in earlier than later flowering species in temperate grassland systems. The effects of warming and N addition on plant phenology are independent of each other. These findings can help to better understand and predict the response of plant phenology to climate warming concurrent with other global change driving factors. PMID:23585496

Effects of Soil Warming and Nitrogen Addition on Soil Respiration in a New Zealand Tussock Grassland

PubMed Central

Graham, Scott L.; Hunt, John E.; Millard, Peter; McSeveny, Tony; Tylianakis, Jason M.; Whitehead, David

2014-01-01

Soil respiration (R S) represents a large terrestrial source of CO2 to the atmosphere. Global change drivers such as climate warming and nitrogen deposition are expected to alter the terrestrial carbon cycle with likely consequences for R S and its components, autotrophic (R A) and heterotrophic respiration (R H). Here we investigate the impacts of a 3°C soil warming treatment and a 50 kg ha−1 y−1 nitrogen addition treatment on R S, R H and their respective seasonal temperature responses in an experimental tussock grassland. Average respiration in untreated soils was 0.96±0.09 μmol m−2 s−1 over the course of the experiment. Soil warming and nitrogen addition increased R S by 41% and 12% respectively. These treatment effects were additive under combined warming and nitrogen addition. Warming increased R H by 37% while nitrogen addition had no effect. Warming and nitrogen addition affected the seasonal temperature response of R S by increasing the basal rate of respiration (R 10) by 14% and 20% respectively. There was no significant interaction between treatments for R 10. The treatments had no impact on activation energy (E 0). The seasonal temperature response of R H was not affected by either warming or nitrogen addition. These results suggest that the additional CO2 emissions from New Zealand tussock grassland soils as a result of warming-enhanced R S constitute a potential positive feedback to rising atmospheric CO2 concentration. PMID:24621790

Enhanced Climatic Warming in the Tibetan Plateau Due to Double CO2: A Model Study

NASA Technical Reports Server (NTRS)

Chen, Baode; Chao, Winston C.; Liu, Xiao-Dong; Lau, William K. M. (Technical Monitor)

2001-01-01

The NCAR (National Center for Atmospheric Research) regional climate model (RegCM2) with time-dependent lateral meteorological fields provided by a 130-year transient increasing CO2 simulation of the NCAR Climate System Model (CSM) has been used to investigate the mechanism of enhanced ground temperature warming over the TP (Tibetan Plateau). From our model results, a remarkable tendency of warming increasing with elevation is found for the winter season, and elevation dependency of warming is not clearly recognized in the summer season. This simulated feature of elevation dependency of ground temperature is consistent with observations. Based on an analysis of surface energy budget, the short wave solar radiation absorbed at the surface plus downward long wave flux reaching the surface shows a strong elevation dependency, and is mostly responsible for enhanced surface warming over the TP. At lower elevations, the precipitation forced by topography is enhanced due to an increase in water vapor supply resulted from a warming in the atmosphere induced by doubling CO2. This precipitation enhancement must be associated with an increase in clouds, which results in a decline in solar flux reaching surface. At higher elevations, large snow depletion is detected in the 2xCO2run. It leads to a decrease in albedo, therefore more solar flux is absorbed at the surface. On the other hand, much more uniform increase in downward long wave flux reaching the surface is found. The combination of these effects (i.e. decrease in solar flux at lower elevations, increase in solar flux at higher elevation and more uniform increase in downward long wave flux) results in elevation dependency of enhanced ground temperature warming over the TP.

Contributions of radiative factors to enhanced dryland warming over East Asia

NASA Astrophysics Data System (ADS)

Zhang, Yanting; Guan, Xiaodan; Yu, Haipeng; Xie, Yongkun; Jin, Hongchun

2017-08-01

Enhanced near-surface atmospheric warming has occurred over East Asia in recent decades, especially in drylands. Although local factors have been confirmed to provide considerable contributions to this warming, such factors have not been sufficiently analyzed. In this study, we extracted the radiatively forced temperature (RFT) associated with the built-up greenhouse gases, aerosol emission, and various other radiative forcing over East Asia and found a close relationship between RFT and CO2. In addition, using climate model experiments, we explored the responses of temperature changes to black carbon (BC), CO2, and SO4 and found that the enhanced dryland warming induced by CO2 had the largest magnitude and was strengthened by the warming effect of BC. Moreover, the sensitivity of daily maximum and minimum temperature changes to BC, CO2, and SO4 was examined. It showed asymmetric responses of daily maximum and minimum temperature to radiative factors, which led to an obvious change of diurnal temperature range (DTR), especially in drylands. The DTR's response to CO2 is the most significant. Therefore, CO2 not only plays a dominant role in enhanced warming but also greatly affects the decrease of DTR in drylands. However, the mechanisms of these radiative factors' effects in the process of DTR change are not clear and require more investigation.

A revised, hazy methane greenhouse for the Archean Earth.

PubMed

Haqq-Misra, Jacob D; Domagal-Goldman, Shawn D; Kasting, Patrick J; Kasting, James F

2008-12-01

Geological and biological evidence suggests that Earth was warm during most of its early history, despite the fainter young Sun. Upper bounds on the atmospheric CO2 concentration in the Late Archean/Paleoproterozoic (2.8-2.2 Ga) from paleosol data suggest that additional greenhouse gases must have been present. Methanogenic bacteria, which were arguably extant at that time, may have contributed to a high concentration of atmospheric CH4, and previous calculations had indicated that a CH4-CO2-H2O greenhouse could have produced warm Late Archean surface temperatures while still satisfying the paleosol constraints on pCO2. Here, we revisit this conclusion. Correction of an error in the CH4 absorption coefficients, combined with the predicted early onset of climatically cooling organic haze, suggest that the amount of greenhouse warming by CH4 was more limited and that pCO2 must therefore have been 0.03 bar, at or above the upper bound of the value obtained from paleosols. Enough warming from CH4 remained in the Archean, however, to explain why Earth's climate cooled and became glacial when atmospheric O2 levels rose in the Paleoproterozoic. Our new model also shows that greenhouse warming by higher hydrocarbon gases, especially ethane (C2H6), may have helped to keep the Late Archean Earth warm.

A comparison of Argo nominal surface and near-surface temperature for validation of AMSR-E SST

NASA Astrophysics Data System (ADS)

Liu, Zenghong; Chen, Xingrong; Sun, Chaohui; Wu, Xiaofen; Lu, Shaolei

2017-05-01

Satellite SST (sea surface temperature) from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) is compared with in situ temperature observations from Argo profiling floats over the global oceans to evaluate the advantages of Argo NST (near-surface temperature: water temperature less than 1 m from the surface). By comparing Argo nominal surface temperature ( 5 m) with its NST, a diurnal cycle caused by daytime warming and nighttime cooling was found, along with a maximum warming of 0.08±0.36°C during 14:00-15:00 local time. Further comparisons between Argo 5-m temperature/Argo NST and AMSR-E SST retrievals related to wind speed, columnar water vapor, and columnar cloud water indicate warming biases at low wind speed (<5 m/s) and columnar water vapor >28 mm during daytime. The warming tendency is more remarkable for AMSR-E SST/Argo 5-m temperature compared with AMSR-E SST/Argo NST, owing to the effect of diurnal warming. This effect of diurnal warming events should be excluded before validation for microwave SST retrievals. Both AMSR-E nighttime SST/Argo 5-m temperature and nighttime SST/Argo NST show generally good agreement, independent of wind speed and columnar water vapor. From our analysis, Argo NST data demonstrated their advantages for validation of satellite-retrieved SST.

Sources of Intermodel Spread in the Lapse Rate and Water Vapor Feedbacks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Po-Chedley, Stephen; Armour, Kyle C.; Bitz, Cecilia M.

Sources of intermodel differences in the global lapse rate (LR) and water vapor (WV) feedbacks are assessed using CO 2 forcing simulations from 28 general circulation models. Tropical surface warming leads to significant warming and moistening in the tropical and extratropical upper troposphere, signifying a nonlocal, tropical influence on extratropical radiation and feedbacks. Model spread in the locally defined LR and WV feedbacks is pronounced in the Southern Ocean because of large-scale ocean upwelling, which reduces surface warming and decouples the surface from the tropospheric response. The magnitude of local extratropical feedbacks across models and over time is well characterizedmore » using the ratio of tropical to extratropical surface warming. It is shown that model differences in locally defined LR and WV feedbacks, particularly over the southern extratropics, drive model variability in the global feedbacks. The cross-model correlation between the global LR and WV feedbacks therefore does not arise from their covariation in the tropics, but rather from the pattern of warming exerting a common control on extratropical feedback responses. Because local feedbacks over the Southern Hemisphere are an important contributor to the global feedback, the partitioning of surface warming between the tropics and the southern extratropics is a key determinant of the spread in the global LR and WV feedbacks. It is also shown that model Antarctic sea ice climatology influences sea ice area changes and southern extratropical surface warming. In conclusion, as a result, model discrepancies in climatological Antarctic sea ice area have a significant impact on the intermodel spread of the global LR and WV feedbacks.« less

Sources of Intermodel Spread in the Lapse Rate and Water Vapor Feedbacks

DOE PAGES

Po-Chedley, Stephen; Armour, Kyle C.; Bitz, Cecilia M.; ...

2018-03-23

Sources of intermodel differences in the global lapse rate (LR) and water vapor (WV) feedbacks are assessed using CO 2 forcing simulations from 28 general circulation models. Tropical surface warming leads to significant warming and moistening in the tropical and extratropical upper troposphere, signifying a nonlocal, tropical influence on extratropical radiation and feedbacks. Model spread in the locally defined LR and WV feedbacks is pronounced in the Southern Ocean because of large-scale ocean upwelling, which reduces surface warming and decouples the surface from the tropospheric response. The magnitude of local extratropical feedbacks across models and over time is well characterizedmore » using the ratio of tropical to extratropical surface warming. It is shown that model differences in locally defined LR and WV feedbacks, particularly over the southern extratropics, drive model variability in the global feedbacks. The cross-model correlation between the global LR and WV feedbacks therefore does not arise from their covariation in the tropics, but rather from the pattern of warming exerting a common control on extratropical feedback responses. Because local feedbacks over the Southern Hemisphere are an important contributor to the global feedback, the partitioning of surface warming between the tropics and the southern extratropics is a key determinant of the spread in the global LR and WV feedbacks. It is also shown that model Antarctic sea ice climatology influences sea ice area changes and southern extratropical surface warming. In conclusion, as a result, model discrepancies in climatological Antarctic sea ice area have a significant impact on the intermodel spread of the global LR and WV feedbacks.« less

Scale-dependency of the global mean surface temperature trend and its implication for the recent hiatus of global warming.

PubMed

Lin, Yong; Franzke, Christian L E

2015-08-11

Studies of the global mean surface temperature trend are typically conducted at a single (usually annual or decadal) time scale. The used scale does not necessarily correspond to the intrinsic scales of the natural temperature variability. This scale mismatch complicates the separation of externally forced temperature trends from natural temperature fluctuations. The hiatus of global warming since 1999 has been claimed to show that human activities play only a minor role in global warming. Most likely this claim is wrong due to the inadequate consideration of the scale-dependency in the global surface temperature (GST) evolution. Here we show that the variability and trend of the global mean surface temperature anomalies (GSTA) from January 1850 to December 2013, which incorporate both land and sea surface data, is scale-dependent and that the recent hiatus of global warming is mainly related to natural long-term oscillations. These results provide a possible explanation of the recent hiatus of global warming and suggest that the hiatus is only temporary.

Does the climate warming hiatus exist over the Tibetan Plateau?

PubMed Central

Duan, Anmin; Xiao, Zhixiang

2015-01-01

The surface air temperature change over the Tibetan Plateau is determined based on historical observations from 1980 to 2013. In contrast to the cooling trend in the rest of China, and the global warming hiatus post-1990s, an accelerated warming trend has appeared over the Tibetan Plateau during 1998–2013 (0.25 °C decade−1), compared with that during 1980–1997 (0.21 °C decade−1). Further results indicate that, to some degree, such an accelerated warming trend might be attributable to cloud–radiation feedback. The increased nocturnal cloud over the northern Tibetan Plateau would warm the nighttime temperature via enhanced atmospheric back-radiation, while the decreased daytime cloud over the southern Tibetan Plateau would induce the daytime sunshine duration to increase, resulting in surface air temperature warming. Meanwhile, the in situ surface wind speed has recovered gradually since 1998, and thus the energy concentration cannot explain the accelerated warming trend over the Tibetan Plateau after the 1990s. It is suggested that cloud–radiation feedback may play an important role in modulating the recent accelerated warming trend over the Tibetan Plateau. PMID:26329678

CAUSES: Diagnosis of the Summertime Warm Bias in CMIP5 Climate Models at the ARM Southern Great Plains Site

NASA Astrophysics Data System (ADS)

Zhang, Chengzhu; Xie, Shaocheng; Klein, Stephen A.; Ma, Hsi-yen; Tang, Shuaiqi; Van Weverberg, Kwinten; Morcrette, Cyril J.; Petch, Jon

2018-03-01

All the weather and climate models participating in the Clouds Above the United States and Errors at the Surface project show a summertime surface air temperature (T2 m) warm bias in the region of the central United States. To understand the warm bias in long-term climate simulations, we assess the Atmospheric Model Intercomparison Project simulations from the Coupled Model Intercomparison Project Phase 5, with long-term observations mainly from the Atmospheric Radiation Measurement program Southern Great Plains site. Quantities related to the surface energy and water budget, and large-scale circulation are analyzed to identify possible factors and plausible links involved in the warm bias. The systematic warm season bias is characterized by an overestimation of T2 m and underestimation of surface humidity, precipitation, and precipitable water. Accompanying the warm bias is an overestimation of absorbed solar radiation at the surface, which is due to a combination of insufficient cloud reflection and clear-sky shortwave absorption by water vapor and an underestimation in surface albedo. The bias in cloud is shown to contribute most to the radiation bias. The surface layer soil moisture impacts T2 m through its control on evaporative fraction. The error in evaporative fraction is another important contributor to T2 m. Similar sources of error are found in hindcast from other Clouds Above the United States and Errors at the Surface studies. In Atmospheric Model Intercomparison Project simulations, biases in meridional wind velocity associated with the low-level jet and the 500 hPa vertical velocity may also relate to T2 m bias through their control on the surface energy and water budget.

Correcting Borehole Temperture Profiles for the Effects of Postglacial Warming

NASA Astrophysics Data System (ADS)

Rath, V.; Gonzalez-Rouco, J. F.

2010-09-01

Though the investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories, there are many open questions concerning the signifcance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last glacial Maximum (LGM) is still present in borehole temperature proiles. It also influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries. This is shown using Monte Carlo experiments on past surface temperature change, using plausible distributions for the most important parameters, i.e.,amplitude and timing of the glacial-interglacial transition, the prior average temperature, and petrophysical properties. It has been argued that the signature of the last glacial-interglacial transition could be responsible for the high amplitudes of millennial temperature reconstructions. However, in shallow boreholes the additional effect of past climate can reasonably approximated by a linear variation of temperature with depth, and thus be accommodated by a "biased" background heat flow. This is good news for borehole climatology. A simple correction based on subtracting an appropriate prior surface temperature history shows promising results reducing these errors considerably, in particular with deeper boreholes, where the warming signal in heat flow can no longer be approximated linearly. We will show examples from North America and Eurasia, comparing temperatures reduced the proposed algoritm with AOGCM modeling results.

More than carbon sequestration: Biophysical climate benefits of restored savanna woodlands.

PubMed

Syktus, Jozef I; McAlpine, Clive A

2016-07-04

Deforestation and climate change are interconnected and represent major environmental challenges. Here, we explore the capacity of regional-scale restoration of marginal agricultural lands to savanna woodlands in Australia to reduce warming and drying resulting from increased concentration of greenhouse gases. We show that restoration triggers a positive feedback loop between the land surface and the atmosphere, characterised by increased evaporative fraction, eddy dissipation and turbulent mixing in the boundary-layer resulting in enhanced cloud formation and precipitation over the restored regions. The increased evapotranspiration results from the capacity deep-rooted woody vegetation to access soil moisture. As a consequence, the increase in precipitation provides additional moisture to soil and trees, thus reinforcing the positive feedback loop. Restoration reduced the rate of warming and drying under the transient increase in the radiative forcing of greenhouse gas emissions (RCP8.5). At the continental scale, average summer warming for all land areas was reduced by 0.18 (o)C from 4.1 (o)C for the period 2056-2075 compared to 1986-2005. For the restored regions (representing 20% of Australia), the averaged surface temperature increase was 3.2 °C which is 0.82 °C cooler compared to agricultural landscapes. Further, there was reduction of 12% in the summer drying of the near-surface soil for the restored regions.

Modeling long-term permafrost degradation

NASA Astrophysics Data System (ADS)

Nicolsky, D.; Romanovsky, V. E.

2017-12-01

Permafrost, as an important part of the Cryosphere, has been also strongly affected by climate warming and a wide spread of the permafrost responses to the warming is currently observed. In particular, at some locations rather slow rates of the permafrost degradations are noticed. We related this behavior to the presence of unfrozen water in frozen fine-grained earth material. In this research, we examine not-very-commonly-discussed heat flux from the ground surface into the permafrost and consequently discuss implications of the unfrozen liquid water content on the long-term thawing of permafrost. We conduct a series of numerical experiments and demonstrate that the presence of fine-grained material with substantial unfrozen liquid water content at below 0C temperature can significantly slow down the thawing rate and hence can increase resilience of permafrost to the warming events. This effect is highly nonlinear and a difference between the rates of thawing in fine- and coarse-grained materials is more drastic for lower values of the incoming into permafrost heat flux. For the high heat flux, the difference between these rates almost disappears. As near-surface permafrost temperature increases towards 0C and the changes in the ground temperature become less evident, the future observation networks should try to incorporate measurements of the unfrozen liquid water content in the near-surface permafrost and heat flux into permafrost in addition to the existing temperature observations.

Rapid and highly variable warming of lake surface waters around the globe

USGS Publications Warehouse

O'Reilly, Catherine; Sharma, Sapna; Gray, Derek; Hampton, Stephanie; Read, Jordan S.; Rowley, Rex J.; Schneider, Philipp; Lenters, John D.; McIntyre, Peter B.; Kraemer, Benjamin M.; Weyhenmeyer, Gesa A.; Straile, Dietmar; Dong, Bo; Adrian, Rita; Allan, Mathew G.; Anneville, Orlane; Arvola, Lauri; Austin, Jay; Bailey, John L.; Baron, Jill S.; Brookes, Justin D; de Eyto, Elvira; Dokulil, Martin T.; Hamilton, David P.; Havens, Karl; Hetherington, Amy L.; Higgins, Scott N.; Hook, Simon; Izmest'eva, Lyubov R.; Jöhnk, Klaus D.; Kangur, Külli; Kasprzak, Peter; Kumagai, Michio; Kuusisto, Esko; Leshkevich, George; Livingstone, David M.; MacIntyre, Sally; May, Linda; Melack, John M.; Mueller-Navara, Doerthe C.; Naumenko, Mikhail; Noges, Peeter; Noges, Tiina; North, Ryan P.; Plisnier, Pierre-Denis; Rigosi, Anna; Rimmer, Alon; Rogora, Michela; Rudstam, Lars G.; Rusak, James A.; Salmaso, Nico; Samal, Nihar R.; Schindler, Daniel E.; Schladow, Geoffrey; Schmid, Martin; Schmidt, Silke R.; Silow, Eugene A.; Soylu, M. Evren; Teubner, Katrin; Verburg, Piet; Voutilainen, Ari; Watkinson, Andrew; Williamson, Craig E.; Zhang, Guoqing

2015-01-01

In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global mean = 0.34°C decade−1) between 1985 and 2009. Our analyses show that surface water warming rates are dependent on combinations of climate and local characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factors—from seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72°C decade−1) to ice-free lakes experiencing increases in air temperature and solar radiation (0.53°C decade−1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.

Effects of Substrate Addition on Soil Respiratory Carbon Release Under Long-Term Warming and Clipping in a Tallgrass Prairie

PubMed Central

Jia, Xiaohong; Zhou, Xuhui; Luo, Yiqi; Xue, Kai; Xue, Xian; Xu, Xia; Yang, Yuanhe; Wu, Liyou; Zhou, Jizhong

2014-01-01

Regulatory mechanisms of soil respiratory carbon (C) release induced by substrates (i.e., plant derived substrates) are critical for predicting ecosystem responses to climate change, but the mechanisms are not well understood. In this study, we sampled soils from a long-term field manipulative experiment and conducted a laboratory incubation to explore the role of substrate supply in regulating the differences in soil C release among the experimental treatments, including control, warming, clipping, and warming plus clipping. Three types of substrates (glucose, C3 and C4 plant materials) were added with an amount equal to 1% of soil dry weight under the four treatments. We found that the addition of all three substrates significantly stimulated soil respiratory C release in all four warming and clipping treatments. In soils without substrate addition, warming significantly stimulated soil C release but clipping decreased it. However, additions of glucose and C3 plant materials (C3 addition) offset the warming effects, whereas C4 addition still showed the warming-induced stimulation of soil C release. Our results suggest that long-term warming may inhibit microbial capacity for decomposition of C3 litter but may enhance it for decomposition of C4 litter. Such warming-induced adaptation of microbial communities may weaken the positive C-cycle feedback to warming due to increased proportion of C4 species in plant community and decreased litter quality. In contrast, clipping may weaken microbial capacity for warming-induced decomposition of C4 litter but may enhance it for C3 litter. Warming- and clipping-induced shifts in microbial metabolic capacity may be strongly associated with changes in plant species composition and could substantially influence soil C dynamics in response to global change. PMID:25490701

Effects of substrate addition on soil respiratory carbon release under long-term warming and clipping in a tallgrass prairie.

PubMed

Jia, Xiaohong; Zhou, Xuhui; Luo, Yiqi; Xue, Kai; Xue, Xian; Xu, Xia; Yang, Yuanhe; Wu, Liyou; Zhou, Jizhong

2014-01-01

Regulatory mechanisms of soil respiratory carbon (C) release induced by substrates (i.e., plant derived substrates) are critical for predicting ecosystem responses to climate change, but the mechanisms are not well understood. In this study, we sampled soils from a long-term field manipulative experiment and conducted a laboratory incubation to explore the role of substrate supply in regulating the differences in soil C release among the experimental treatments, including control, warming, clipping, and warming plus clipping. Three types of substrates (glucose, C3 and C4 plant materials) were added with an amount equal to 1% of soil dry weight under the four treatments. We found that the addition of all three substrates significantly stimulated soil respiratory C release in all four warming and clipping treatments. In soils without substrate addition, warming significantly stimulated soil C release but clipping decreased it. However, additions of glucose and C3 plant materials (C3 addition) offset the warming effects, whereas C4 addition still showed the warming-induced stimulation of soil C release. Our results suggest that long-term warming may inhibit microbial capacity for decomposition of C3 litter but may enhance it for decomposition of C4 litter. Such warming-induced adaptation of microbial communities may weaken the positive C-cycle feedback to warming due to increased proportion of C4 species in plant community and decreased litter quality. In contrast, clipping may weaken microbial capacity for warming-induced decomposition of C4 litter but may enhance it for C3 litter. Warming- and clipping-induced shifts in microbial metabolic capacity may be strongly associated with changes in plant species composition and could substantially influence soil C dynamics in response to global change.

Century-Long Warming Trends in the Upper Water Column of Lake Tanganyika.

PubMed

Kraemer, Benjamin M; Hook, Simon; Huttula, Timo; Kotilainen, Pekka; O'Reilly, Catherine M; Peltonen, Anu; Plisnier, Pierre-Denis; Sarvala, Jouko; Tamatamah, Rashid; Vadeboncoeur, Yvonne; Wehrli, Bernhard; McIntyre, Peter B

2015-01-01

Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX86) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate change. Here, we use a comprehensive database of in situ temperature data from the top 100 meters of the water column that span the lake's seasonal range and lateral extent to demonstrate that long-term temperature trends in Lake Tanganyika depend strongly on depth, season, and latitude. The observed spatiotemporal variation in surface warming rates accounts for small differences between warming rate estimates from in situ instruments and satellite data. However, after accounting for spatiotemporal variation in temperature and warming rates, the TEX86 paleolimnological proxy yields lower surface temperatures (1.46 °C lower on average) and faster warming rates (by a factor of three) than in situ measurements. Based on the ecology of Thaumarchaeota (the microbes whose biomolecules are involved with generating the TEX86 proxy), we offer a reinterpretation of the TEX86 data from Lake Tanganyika as the temperature of the low-oxygen zone, rather than of the lake surface temperature as has been suggested previously. Our analyses provide a thorough accounting of spatiotemporal variation in warming rates, offering strong evidence that thermal and ecological shifts observed in this massive tropical lake over the last century are robust and in step with global climate change.

An Assessment of the SST Simulation Using the Climate Forecast System Coupled to the SSiB Surface Model

NASA Astrophysics Data System (ADS)

Wang, Y.; Xue, Y.; Huang, B.; Lee, J.; De Sales, F.

2016-12-01

A long term simulation has been conducted using the Climate Forecast System (CFSv2) coupled to the SSiB-2 land model, which consists of the Global Forecast System atmospheric model (GFS) and the Modular Ocean model - version 4 (MOM4) as the ocean component. This study evaluates the model's performance in simulating sea surface temperature (SST) mean state, trend, and inter-annual and decadal variabilities. The model is able to produce the reasonable spatial distribution of the SST climatology; however, it has prominent large scale biases. In the middle latitude of the Northern Hemisphere, major cold biases is close to the warm side of the large SST gradients, which may be associated with the weaker Kuroshio and Gulf Stream extensions that diffuse the SST gradient. IN addition, warm biases extend along the west coast of the North America continent to the high latitude, which may be related with excessive Ekman down-welling and solar radiation fluxes reaching to the surface due to the lack of cloud there. Warm biases also exist over the tropical cold tough areas in the Pacific and Atlantic. The global SST trend and interannual variations are well captured except for that in the south Hemisphere after year 2000, which is mainly contributed by the bias from the southern Pacific Ocean. Although the model fails to accurately produce ENSO events in proper years, it does reproduce the ENSO frequency well; they are skewed toward more warm events after 1990. The model also shows ability in SST decadal variation, such as the so-called inter-decadal Pacific oscillation (IPO); however, its phases seem to go reversely compared with the observation.

What caused the Extreme Storm Season over the North Atlantic and the UK in Winter 2013-14?

NASA Astrophysics Data System (ADS)

Leckebusch, G. C.; Wild, S.; Befort, D. J.

2015-12-01

In winter 2013-2014, the UK experienced exceptional stormy and rainy weather conditions. Concurrently, surface temperatures over large parts of central North America fell to near record minimum values. One potential driver for these cold conditions is discussed to be the increasingly warm surface waters of the tropical west Pacific. It has been suggested these increasing sea surface temperatures could also be the cause for extreme weather over the British Isles. Testing this hypothesis, we investigate mechanisms linking the tropical west Pacific and European wind storm activity. We focus on two research questions. Firstly: Was a chain of anomaly patterns with origin in the west Pacific present in the winter 2013-14? And secondly: Can centres of action along such a chain be identified with a strong interannual relationship in the recent past? Our results, using primarily ERA-Interim Reanalysis from 1979 to 2014, show an absolute maximum of wind storm frequency over the northeast Atlantic and the British Isles in winter 2013-14. We also find absolute minimum surface temperatures in central North America and increased convective activity over the tropical west Pacific in the same season. The winter 2013-14 was additionally characterized by anomalous warm sea surface temperatures over the subtropical northwest Atlantic. Although the interannual variability of wind storms in the northeast Atlantic and surface temperatures in North America are significantly anti-correlated, we cannot directly relate wind storm frequency with tropical west Pacific anomalies. We thus conclude that the conditions over the Pacific in winter 2013-14 were favourable but not sufficient to explain the record number of wind storms in this season. Instead, we suggest that warm north Atlantic sea surface temperature anomalies in combination with cold surface temperatures over North America played a more important role for generating higher wind storm counts over the northeast Atlantic and the UK.

An energy balance model exploration of the impacts of interactions between surface albedo, cloud cover and water vapor on polar amplification

NASA Astrophysics Data System (ADS)

Södergren, A. Helena; McDonald, Adrian J.; Bodeker, Gregory E.

2017-11-01

We examine the effects of non-linear interactions between surface albedo, water vapor and cloud cover (referred to as climate variables) on amplified warming of the polar regions, using a new energy balance model. Our simulations show that the sum of the contributions to surface temperature changes due to any variable considered in isolation is smaller than the temperature changes from coupled feedback simulations. This non-linearity is strongest when all three climate variables are allowed to interact. Surface albedo appears to be the strongest driver of this non-linear behavior, followed by water vapor and clouds. This is because increases in longwave radiation absorbed by the surface, related to increases in water vapor and clouds, and increases in surface absorbed shortwave radiation caused by a decrease in surface albedo, amplify each other. Furthermore, our results corroborate previous findings that while increases in cloud cover and water vapor, along with the greenhouse effect itself, warm the polar regions, water vapor also significantly warms equatorial regions, which reduces polar amplification. Changes in surface albedo drive large changes in absorption of incoming shortwave radiation, thereby enhancing surface warming. Unlike high latitudes, surface albedo change at low latitudes are more constrained. Interactions between surface albedo, water vapor and clouds drive larger increases in temperatures in the polar regions compared to low latitudes. This is in spite of the fact that, due to a forcing, cloud cover increases at high latitudes and decreases in low latitudes, and that water vapor significantly enhances warming at low latitudes.

Changes in Arctic Vegetation Amplify High-Latitude Warming Through Greenhouse Effect

NASA Astrophysics Data System (ADS)

Swann, A.; Fung, I.; Levis, S.; Bonan, G. B.; Doney, S. C.

2009-12-01

Changes in vegetation cover are recognized to modify climate and the energy budget of the Earth through changes in albedo in high latitudes and evapotranspiration (ET) in the tropics. In snow-covered regions, the springtime growth of leaves enhances solar absorption because surface albedo is reduced from the albedo of snow (~0.8) towards the albedo of leaves (~0.1). Leaves also play a hydrologic role, transpiring soil water to the atmosphere. It has been suggested that broad-leaf deciduous trees may invade warming tundra more effectively than boreal evergreen trees and these trees have higher rates of transpiration than needle-leaf trees. Here we use a global climate model with an interactive biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is 2.4 times larger than the direct forcing due to albedo change from the forest. Albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration. Furthermore, the greenhouse warming by additional water vapor melts sea ice and triggers a positive feedback through changes in ocean albedo and evaporation. Vegetation feedbacks through albedo and transpiration produce a strong warming if they act in combination with sea-ice processes.

Optimal weighting of data to detect climatic change - Application to the carbon dioxide problem

NASA Technical Reports Server (NTRS)

Bell, T. L.

1982-01-01

It is suggested that a weighting of surface temperature data, using information about the expected level of warming in different seasons and geographical regions and statistical information about the amount of natural variability in surface temperature, can improve the chances of early detection of carbon dioxide concentration-induced climatic warming. A preliminary analysis of the optimal weighting method presented suggests that it is 25 per cent more effective in revealing surface warming than the conventional method, in virtue of the fact that 25 per cent more data must conventionally be analyzed in order to arrive at a similar probability of detection. An approximate calculation suggests that the warming ought to have already been detected, if the only sources of significant surface temperature variability had time scales of less than one year.

Warming and Nitrogen Addition Alter Photosynthetic Pigments, Sugars and Nutrients in a Temperate Meadow Ecosystem.

PubMed

Zhang, Tao; Yang, Shaobo; Guo, Rui; Guo, Jixun

2016-01-01

Global warming and nitrogen (N) deposition have an important influence on terrestrial ecosystems; however, the influence of warming and N deposition on plant photosynthetic products and nutrient cycling in plants is not well understood. We examined the effects of 3 years of warming and N addition on the plant photosynthetic products, foliar chemistry and stoichiometric ratios of two dominant species, i.e., Leymus chinensis and Phragmites communis, in a temperate meadow in northeastern China. Warming significantly increased the chlorophyll content and soluble sugars in L. chinensis but had no impact on the carotenoid and fructose contents. N addition caused a significant increase in the carotenoid and fructose contents. Warming and N addition had little impact on the photosynthetic products of P. communis. Warming caused significant decreases in the N and phosphorus (P) concentrations and significantly increased the carbon (C):P and N:P ratios of L. chinensis, but not the C concentration or the C:N ratio. N addition significantly increased the N concentration, C:P and N:P ratios, but significantly reduced the C:N ratio of L. chinensis. Warming significantly increased P. communis C and P concentrations, and the C:N and C:P ratios, whereas N addition increased the C, N and P concentrations but had no impact on the stoichiometric variables. This study suggests that both warming and N addition have direct impacts on plant photosynthates and elemental stoichiometry, which may play a vital role in plant-mediated biogeochemical cycling in temperate meadow ecosystems.

Do radiative feedbacks depend on the structure and type of climate forcing, or only on the spatial pattern of surface temperature change?

NASA Astrophysics Data System (ADS)

Haugstad, A.; Battisti, D. S.; Armour, K.

2016-12-01

Earth's climate sensitivity depends critically on the strength of radiative feedbacks linking surface warming to changes in top-of-atmosphere (TOA) radiation. Many studies use a simplistic idea of radiative feedbacks, either by treating them as global mean quantities, or by assuming they can be defined uniquely by geographic location and thus that TOA radiative response depends only on local surface warming. For example, a uniform increase in sea-surface temperature has been widely used as a surrogate for global warming (e.g., Cess et al 1990 and the CMIP 'aqua4k' simulations), with the assumption that this produces the same radiative feedbacks as those arising from a doubling of carbon dioxide - even though the spatial patterns of warming differ. However, evidence suggests that these assumptions are not valid, and local feedbacks may be integrally dependent on the structure of warming or type of climate forcing applied (Rose et al 2014). This study thus investigates the following questions: to what extent do local feedbacks depend on the structure and type of forcing applied? And, to what extent do they depend on the pattern of surface temperature change induced by that forcing? Using an idealized framework of an aquaplanet atmosphere-only model, we show that radiative feedbacks are indeed dependent on the large scale structure of warming and type of forcing applied. For example, the climate responds very differently to two forcings of equal global magnitude but applied in different global regions; the pattern of local feedbacks arising from uniform warming are not the same as that arising from polar amplified warming; and the same local feedbacks can be induced by distinct forcing patterns, provided that they produce the same pattern of surface temperature change. These findings suggest that the so-called `efficacies' of climate forcings can be understood simply in terms of how local feedbacks depend on the temperature patterns they induce.

Spurious Additional Warming Reconstructed From Borehole Temperatures Corrected for the Effect of the Last Glacial Cycle

NASA Astrophysics Data System (ADS)

Šafanda, Jan

2018-03-01

Reconstructions of past ground surface temperature changes from temperature logs conducted in several hundred meter deep boreholes have proved to be a valuable independent source of information on climate variations over the last millennium. The reconstruction techniques have been evolving for more than two decades to extract optimally the climate signal of the last millennium contained in the temperature logs of different length performed in sites with different histories of the Last Glacial Cycle. This paper analyzes the method of the Last Glacial Cycle thermal effect removal from such borehole temperature profiles used by Beltrami et al. (2017, https://doi.org/10.1002/2016GL071317) in reconstructing the last 500 year history. I show that the reported results of additional warming in this period reconstructed from the corrected borehole data for North America are an artifact generated by the correction.

Distinctive ocean interior changes during the recent warming slowdown

PubMed Central

Cheng, Lijing; Zheng, Fei; Zhu, Jiang

2015-01-01

The earth system experiences continuous heat input, but a “climate hiatus” of upper ocean waters has been observed in this century. This leads to a question: where is the extra heat going? Using four in situ observation datasets, we explore the ocean subsurface temperature changes from 2004 to 2013. The observations all show that the ocean has continued to gain heat in this century, which is indicative of anthropogenic global warming. However, a distinctive pattern of change in the interior ocean is observed. The sea surface (1–100 m) temperature has decreased in this century, accompanied by warming in the 101–300 m layer. This pattern is due to the changes in the frequency of El Niño and La Niña events (ENSO characteristics), according to both observations and CMIP5 model simulations. In addition, we show for the first time that the ocean subsurface within 301–700 m experienced a net cooling, indicative of another instance of variability in the natural ocean. Furthermore, the ocean layer of 701–1500 m has experienced significant warming. PMID:26394551

Distinctive ocean interior changes during the recent warming slowdown.

PubMed

Cheng, Lijing; Zheng, Fei; Zhu, Jiang

2015-09-23

The earth system experiences continuous heat input, but a "climate hiatus" of upper ocean waters has been observed in this century. This leads to a question: where is the extra heat going? Using four in situ observation datasets, we explore the ocean subsurface temperature changes from 2004 to 2013. The observations all show that the ocean has continued to gain heat in this century, which is indicative of anthropogenic global warming. However, a distinctive pattern of change in the interior ocean is observed. The sea surface (1-100 m) temperature has decreased in this century, accompanied by warming in the 101-300 m layer. This pattern is due to the changes in the frequency of El Niño and La Niña events (ENSO characteristics), according to both observations and CMIP5 model simulations. In addition, we show for the first time that the ocean subsurface within 301-700 m experienced a net cooling, indicative of another instance of variability in the natural ocean. Furthermore, the ocean layer of 701-1500 m has experienced significant warming.

Quantifying the ice-albedo feedback through decoupling

NASA Astrophysics Data System (ADS)

Kravitz, B.; Rasch, P. J.

2017-12-01

The ice-albedo feedback involves numerous individual components, whereby warming induces sea ice melt, inducing reduced surface albedo, inducing increased surface shortwave absorption, causing further warming. Here we attempt to quantify the sea ice albedo feedback using an analogue of the "partial radiative perturbation" method, but where the governing mechanisms are directly decoupled in a climate model. As an example, we can isolate the insulating effects of sea ice on surface energy and moisture fluxes by allowing sea ice thickness to change but fixing Arctic surface albedo, or vice versa. Here we present results from such idealized simulations using the Community Earth System Model in which individual components are successively fixed, effectively decoupling the ice-albedo feedback loop. We isolate the different components of this feedback, including temperature change, sea ice extent/thickness, and air-sea exchange of heat and moisture. We explore the interactions between these different components, as well as the strengths of the total feedback in the decoupled feedback loop, to quantify contributions from individual pieces. We also quantify the non-additivity of the effects of the components as a means of investigating the dominant sources of nonlinearity in the ice-albedo feedback.

Insights into Ocean Acidification During the Middle Eocene Climatic Optimum from Boron Isotopes at Southern Ocean Site 738

NASA Astrophysics Data System (ADS)

Moebius, I.; Hoenisch, B.; Friedrich, O.

2015-12-01

The Middle Eocene Climatic Optimum (MECO) is a ~650-kyr interval of global warming, with a brief ~50 ky long peak warming interval, and an abrupt termination. Deep sea and surface ocean temperature evolution across this interval are fairly well constrained, but thus far we have little understanding of the mechanisms responsible for the gradual warming and rapid recovery. Carbonate mass accumulation rates suggest a shoaling of the carbonate compensation depth, and studies on alkenones indicate increasing atmospheric CO2 levels during the MECO. This suggests an increase in surface ocean CO2, and consequently ocean acidification. However, the severity and timing of the proposed ocean acidification with respect to the onset, peak warming and the termination are currently not well resolved. The boron isotopic composition (δ11B) recorded in planktic foraminifer shells offers an opportunity to infer oceanic pH across this interval. We are working on a boron isotope reconstruction from Southern Ocean IODP site 738 and South Atlantic IODP site 1263, covering 42.0 to 38.5 Ma. These sites are characterized by good carbonate preservation and well-defined age models have been established. Additionally, ecology, nutrient content and bottom-water oxygenation have been shown to change significantly across the event towards a more eutrophic, periodically oxygen-depleted environment supporting different biological communities. We selected the planktic foraminifera species Acarinina spinuloinflata for this study because it is symbiont-bearing, suggesting a near-surface habitat and little vertical migration in the water column, and because of its abundance in the samples. δ11B data will be translated to surface ocean pH and atmospheric pCO2 will be approximated to refine knowledge about the carbon cycle during this time. Parallel analysis of two core sites will help to evaluate the tenacity of the data.

Surface wave effects on water temperature in the Baltic Sea: simulations with the coupled NEMO-WAM model

NASA Astrophysics Data System (ADS)

Alari, Victor; Staneva, Joanna; Breivik, Øyvind; Bidlot, Jean-Raymond; Mogensen, Kristian; Janssen, Peter

2016-08-01

Coupled circulation (NEMO) and wave model (WAM) system was used to study the effects of surface ocean waves on water temperature distribution and heat exchange at regional scale (the Baltic Sea). Four scenarios—including Stokes-Coriolis force, sea-state dependent energy flux (additional turbulent kinetic energy due to breaking waves), sea-state dependent momentum flux and the combination these forcings—were simulated to test the impact of different terms on simulated temperature distribution. The scenario simulations were compared to a control simulation, which included a constant wave-breaking coefficient, but otherwise was without any wave effects. The results indicate a pronounced effect of waves on surface temperature, on the distribution of vertical temperature and on upwelling's. Overall, when all three wave effects were accounted for, did the estimates of temperature improve compared to control simulation. During the summer, the wave-induced water temperature changes were up to 1 °C. In northern parts of the Baltic Sea, a warming of the surface layer occurs in the wave included simulations in summer months. This in turn reduces the cold bias between simulated and measured data, e.g. the control simulation was too cold compared to measurements. The warming is related to sea-state dependent energy flux. This implies that a spatio-temporally varying wave-breaking coefficient is necessary, because it depends on actual sea state. Wave-induced cooling is mostly observed in near-coastal areas and is the result of intensified upwelling in the scenario, when Stokes-Coriolis forcing is accounted for. Accounting for sea-state dependent momentum flux results in modified heat exchange at the water-air boundary which consequently leads to warming of surface water compared to control simulation.

Trends in Northern Hemisphere surface cyclone frequency and intensity

USGS Publications Warehouse

McCabe, G.J.; Clark, M.P.; Serreze, Mark C.

2001-01-01

One of the hypothesized effects of global warming from increasing concentrations of greenhouse gases is a change in the frequency and/or intensity of extratropical cyclones. In this study, winter frequencies and intensities of extratropical cyclones in the Northern Hemisphere for the period 1959-97 are examined to determine if identifiable trends are occurring. Results indicate a statistically significant decrease in midlatitude cyclone frequency and a significant increase in high-latitude cyclone frequency. In addition, storm intensity has increased in both the high and midlatitudes. The changes in storm frequency correlate with changes in winter Northern Hemisphere temperature and support hypotheses that global warming may result in a northward shift of storm tracks in the Northern Hemisphere.

ENSO Transition Asymmetry: Internal and External Causes and Intermodel Diversity

NASA Astrophysics Data System (ADS)

An, Soon-Il; Kim, Ji-Won

2018-05-01

El Niño is frequently followed by La Niña, but the opposite case rarely happens. Here we explore a mechanism for such an asymmetrical transition and its future changes. Internally, the asymmetrical response of upper ocean waves against surface wind stress anomaly exerts a primary cause of El Niño-Southern Oscillation (ENSO) transition asymmetry. Externally, the asymmetrical capacitor effects of both Indian and Atlantic Oceans play some roles in driving the ENSO transition asymmetry via the interbasin interactions. The historical runs of Coupled Model Intercomparison Project Phase 5 show that the intermodel transition asymmetry is significantly correlated with the intermodel asymmetry in ocean wave response to surface wind forcing but not with that in the interbasin interactions. In addition, the El Niño-to-La Niña transition tendency was weaker in moderate global warming scenario runs (Representative Concentration Pathway 4.5) while slightly enhanced in strong warming scenario runs (Representative Concentration Pathway 8.5). Similar changes also appeared in the asymmetrical response of ocean waves against the surface wind forcing.

The effect of active warming in prehospital trauma care during road and air ambulance transportation - a clinical randomized trial.

PubMed

Lundgren, Peter; Henriksson, Otto; Naredi, Peter; Björnstig, Ulf

2011-10-21

Prevention and treatment of hypothermia by active warming in prehospital trauma care is recommended but scientific evidence of its effectiveness in a clinical setting is scarce. The objective of this study was to evaluate the effect of additional active warming during road or air ambulance transportation of trauma patients. Patients were assigned to either passive warming with blankets or passive warming with blankets with the addition of an active warming intervention using a large chemical heat pad applied to the upper torso. Ear canal temperature, subjective sensation of cold discomfort and vital signs were monitored. Mean core temperatures increased from 35.1°C (95% CI; 34.7-35.5°C) to 36.0°C (95% CI; 35.7-36.3°C) (p < 0.05) in patients assigned to passive warming only (n = 22) and from 35.6°C (95% CI; 35.2-36.0°C) to 36.4°C (95% CI; 36.1-36.7°C) (p < 0.05) in patients assigned to additional active warming (n = 26) with no significant differences between the groups. Cold discomfort decreased in 2/3 of patients assigned to passive warming only and in all patients assigned to additional active warming, the difference in cold discomfort change being statistically significant (p < 0.05). Patients assigned to additional active warming also presented a statistically significant decrease in heart rate and respiratory frequency (p < 0.05). In mildly hypothermic trauma patients, with preserved shivering capacity, adequate passive warming is an effective treatment to establish a slow rewarming rate and to reduce cold discomfort during prehospital transportation. However, the addition of active warming using a chemical heat pad applied to the torso will significantly improve thermal comfort even further and might also reduce the cold induced stress response. ClinicalTrials.gov: NCT01400152.

Global Sea Surface Temperature and Ecosystem Change Across the Mid-Miocene Climatic Optimum

NASA Astrophysics Data System (ADS)

Veenstra, T. J. T.; Bakker, V. B.; Sangiorgi, F.; Peterse, F.; Schouten, S.; Sluijs, A.

2016-12-01

Even though the term Mid-Miocene Climatic Optimum (MMCO; ca. 17 to 14 Ma) has been widely used in the literature since the early 1990's, almost no early-middle Miocene sea surface temperature (SST) proxy records have been published that support climate warming across its onset. Benthic (and diagenetically altered planktic) foram δ18O records show a decrease, suggesting (deep) ocean warming and/or Antarctic ice sheet melting. However, reliable absolute SST proxy records are absent from the tropics and very scarce in temperate and polar regions. This leaves the question if the warmth of the MMCO was truly global and how its onset relates to the widely recorded positive (Monterey) carbon isotope excursion and volcanism. Finally, it remains uncertain how marine ecosystems responded to this hypothesized warming. We present organic biomarker SST proxy records (Uk'37 and TEX86) spanning the MMCO for several locations in the Atlantic and Pacific Ocean along a pole-to-pole transect, including Ocean Drilling Program Site 959 in the eastern Tropical Atlantic, ODP Site 643 in the Norwegian Sea, ODP Site 1007 on the Great Bahama Bank and Integrated Ocean Drilling Program Site U1352 off New Zealand. Additionally, we use marine palynology (mostly dinoflagellate cysts) to assess ecosystem change at these locations. The resulting spatial reconstruction of SST change shows that Middle Miocene warming was global. Nevertheless, the records also show distinct regional variability, including relatively large warming in the Norwegian Sea and a damped signal in the southern hemisphere, suggesting pronounced changes in ocean circulation. The onset of the MMCO was marked by prominent changes in ecological and depositional setting at the studied sites, likely also related to ocean circulation changes.

Understanding recent climate change.

PubMed

Serreze, Mark C

2010-02-01

The Earth's atmosphere has a natural greenhouse effect, without which the global mean surface temperature would be about 33 degrees C lower and life would not be possible. Human activities have increased atmospheric concentrations of carbon dioxide, methane, and other gases in trace amounts. This has enhanced the greenhouse effect, resulting in surface warming. Were it not for the partly offsetting effects of increased aerosol concentrations, the increase in global mean surface temperature over the past 100 years would be larger than observed. Continued surface warming through the 21st century is inevitable and will likely have widespread ecological impacts. The magnitude and rate of warming for the global average will be largely dictated by the strength and direction of climate feedbacks, thermal inertia of the oceans, the rate of greenhouse gas emissions, and aerosol concentrations. Because of regional expressions of climate feedbacks, changes in atmospheric circulation, and a suite of other factors, the magnitude and rate of warming and changes in other key climate elements, such as precipitation, will not be uniform across the planet. For example, due to loss of its floating sea-ice cover, the Arctic will warm the most.

Desert Amplification in a Warming Climate

PubMed Central

Zhou, Liming

2016-01-01

Here I analyze the observed and projected surface temperature anomalies over land between 50°S-50°N for the period 1950–2099 by large-scale ecoregion and find strongest warming consistently and persistently seen over driest ecoregions such as the Sahara desert and the Arabian Peninsula during various 30-year periods, pointing to desert amplification in a warming climate. This amplification enhances linearly with the global mean greenhouse gases(GHGs) radiative forcing and is attributable primarily to a stronger GHGs-enhanced downward longwave radiation forcing reaching the surface over drier ecoregions as a consequence of a warmer and thus moister atmosphere in response to increasing GHGs. These results indicate that desert amplification may represent a fundamental pattern of global warming associated with water vapor feedbacks over land in low- and mid- latitudes where surface warming rates depend inversely on ecosystem dryness. It is likely that desert amplification might involve two types of water vapor feedbacks that maximize respectively in the tropical upper troposphere and near the surface over deserts, with both being very dry and thus extremely sensitive to changes of water vapor. PMID:27538725

Long-Term Warming Shifts the Composition of Bacterial Communities in the Phyllosphere of Galium album in a Permanent Grassland Field-Experiment

PubMed Central

Aydogan, Ebru L.; Moser, Gerald; Müller, Christoph; Kämpfer, Peter; Glaeser, Stefanie P.

2018-01-01

Global warming is currently a much discussed topic with as yet largely unexplored consequences for agro-ecosystems. Little is known about the warming effect on the bacterial microbiota inhabiting the plant surface (phyllosphere), which can have a strong impact on plant growth and health, as well as on plant diseases and colonization by human pathogens. The aim of this study was to investigate the effect of moderate surface warming on the diversity and composition of the bacterial leaf microbiota of the herbaceous plant Galium album. Leaves were collected from four control and four surface warmed (+2°C) plots located at the field site of the Environmental Monitoring and Climate Impact Research Station Linden in Germany over a 6-year period. Warming had no effect on the concentration of total number of cells attached to the leaf surface as counted by Sybr Green I staining after detachment, but changes in the diversity and phylogenetic composition of the bacterial leaf microbiota analyzed by bacterial 16S rRNA gene Illumina amplicon sequencing were observed. The bacterial phyllosphere microbiota were dominated by Proteobacteria, Bacteroidetes, and Actinobacteria. Warming caused a significant higher relative abundance of members of the Gammaproteobacteria, Actinobacteria, and Firmicutes, and a lower relative abundance of members of the Alphaproteobacteria and Bacteroidetes. Plant beneficial bacteria like Sphingomonas spp. and Rhizobium spp. occurred in significantly lower relative abundance in leaf samples of warmed plots. In contrast, several members of the Enterobacteriaceae, especially Enterobacter and Erwinia, and other potential plant or human pathogenic genera such as Acinetobacter and insect-associated Buchnera and Wolbachia spp. occurred in higher relative abundances in the phyllosphere samples from warmed plots. This study showed for the first time the long-term impact of moderate (+2°C) surface warming on the phyllosphere microbiota on plants. A reduction of beneficial bacteria and an enhancement of potential pathogenic bacteria in the phyllosphere of plants may indicate that this aspect of the ecosystem which has been largely neglected up till now, can be a potential risk for pathogen transmission in agro-ecosystems in the near future. PMID:29487575

Long-Term Warming Shifts the Composition of Bacterial Communities in the Phyllosphere of Galium album in a Permanent Grassland Field-Experiment.

PubMed

Aydogan, Ebru L; Moser, Gerald; Müller, Christoph; Kämpfer, Peter; Glaeser, Stefanie P

2018-01-01

Global warming is currently a much discussed topic with as yet largely unexplored consequences for agro-ecosystems. Little is known about the warming effect on the bacterial microbiota inhabiting the plant surface (phyllosphere), which can have a strong impact on plant growth and health, as well as on plant diseases and colonization by human pathogens. The aim of this study was to investigate the effect of moderate surface warming on the diversity and composition of the bacterial leaf microbiota of the herbaceous plant Galium album . Leaves were collected from four control and four surface warmed (+2°C) plots located at the field site of the Environmental Monitoring and Climate Impact Research Station Linden in Germany over a 6-year period. Warming had no effect on the concentration of total number of cells attached to the leaf surface as counted by Sybr Green I staining after detachment, but changes in the diversity and phylogenetic composition of the bacterial leaf microbiota analyzed by bacterial 16S rRNA gene Illumina amplicon sequencing were observed. The bacterial phyllosphere microbiota were dominated by Proteobacteria , Bacteroidetes , and Actinobacteria . Warming caused a significant higher relative abundance of members of the Gammaproteobacteria , Actinobacteria , and Firmicutes , and a lower relative abundance of members of the Alphaproteobacteria and Bacteroidetes . Plant beneficial bacteria like Sphingomonas spp. and Rhizobium spp. occurred in significantly lower relative abundance in leaf samples of warmed plots. In contrast, several members of the Enterobacteriaceae , especially Enterobacter and Erwinia , and other potential plant or human pathogenic genera such as Acinetobacter and insect-associated Buchnera and Wolbachia spp. occurred in higher relative abundances in the phyllosphere samples from warmed plots. This study showed for the first time the long-term impact of moderate (+2°C) surface warming on the phyllosphere microbiota on plants. A reduction of beneficial bacteria and an enhancement of potential pathogenic bacteria in the phyllosphere of plants may indicate that this aspect of the ecosystem which has been largely neglected up till now, can be a potential risk for pathogen transmission in agro-ecosystems in the near future.

Forests tend to cool the land surface in the temperate zone: An analysis of the mechanisms controlling radiometric surface temperature change in managed temperate ecosystems

NASA Astrophysics Data System (ADS)

Stoy, P. C.; Katul, G. G.; Juang, J.; Siqueira, M. B.; Novick, K. A.; Essery, R.; Dore, S.; Kolb, T. E.; Montes-Helu, M. C.; Scott, R. L.

2010-12-01

Vegetation is an important control on the surface energy balance and thereby surface temperature. Boreal forests and arctic shrubs are thought to warm the land surface by absorbing more radiation than the vegetation they replace. The surface temperatures of tropical forests tend to be cooler than deforested landscapes due to enhanced evapotranspiration. The effects of reforestation on surface temperature change in the temperate zone is less-certain, but recent modeling efforts suggest forests have a global warming effect. We quantified the mechanisms driving radiometric surface changes following landcover changes using paired ecosystem case studies from the Ameriflux database with energy balance models of varying complexity. Results confirm previous findings that deciduous and coniferous forests in the southeastern U.S. are ca. 1 °C cooler than an adjacent field on an annual basis because aerodynamic/ecophysiological cooling of 2-3 °C outweighs an albedo-related warming of <1 °C. A 50-70% reduction in the aerodynamic resistance to sensible and latent heat exchange in the forests dominated the cooling effect. A grassland ecosystem that succeeded a stand-replacing ponderosa pine fire was ca. 1 °C warmer than unburned stands because a 1.5 °C aerodynamic warming offset a slight surface cooling due to greater albedo and soil heat flux. An ecosystem dominated by mesquite shrub encroachment was nearly 2 °C warmer than a native grassland ecosystem as aerodynamic and albedo-related warming outweighed a small cooling effect due to changes in soil heat flux. The forested ecosystems in these case studies are documented to have higher carbon uptake than the non-forested systems. Results suggest that temperate forests tend to cool the land surface and suggest that previous model-based findings that forests warm the Earth’s surface globally should be reconsidered.Changes to radiometric surface temperature (K) following changes in vegetation using paired ecosystem case studies C4 grassland and shrub ecosystem surface temperatures were adjusted for differences in air temperature across sites.

The Great Lakes' regional climate regimes

NASA Astrophysics Data System (ADS)

Sugiyama, Noriyuki

For the last couple of decades, the Great Lakes have undergone rapid surface warming. In particular, the magnitude of the summer surface-warming trends of the Great Lakes have been much greater than those of surrounding land (Austin and Colman, 2007). Among the Great Lakes, the deepest Lake Superior exhibited the strongest warming trend in its annual, as well as summer surface water temperature. We find that many aspects of this behavior can be explained in terms of the tendency of deep lakes to exhibit multiple regimes characterized, under the same seasonally varying forcing, by the warmer and colder seasonal cycles exhibiting different amounts of wintertime lake-ice cover and corresponding changes in the summertime lake-surface temperatures. In this thesis, we address the problem of the Great Lakes' warming using one-dimensional lake modeling to interpret diverse observations of the recent lake behavior. (Abstract shortened by ProQuest.).

On avoiding dangerous anthropogenic interference with the climate system: formidable challenges ahead.

PubMed

Ramanathan, V; Feng, Y

2008-09-23

The observed increase in the concentration of greenhouse gases (GHGs) since the preindustrial era has most likely committed the world to a warming of 2.4 degrees C (1.4 degrees C to 4.3 degrees C) above the preindustrial surface temperatures. The committed warming is inferred from the most recent Intergovernmental Panel on Climate Change (IPCC) estimates of the greenhouse forcing and climate sensitivity. The estimated warming of 2.4 degrees C is the equilibrium warming above preindustrial temperatures that the world will observe even if GHG concentrations are held fixed at their 2005 concentration levels but without any other anthropogenic forcing such as the cooling effect of aerosols. The range of 1.4 degrees C to 4.3 degrees C in the committed warming overlaps and surpasses the currently perceived threshold range of 1 degrees C to 3 degrees C for dangerous anthropogenic interference with many of the climate-tipping elements such as the summer arctic sea ice, Himalayan-Tibetan glaciers, and the Greenland Ice Sheet. IPCC models suggest that approximately 25% (0.6 degrees C) of the committed warming has been realized as of now. About 90% or more of the rest of the committed warming of 1.6 degrees C will unfold during the 21st century, determined by the rate of the unmasking of the aerosol cooling effect by air pollution abatement laws and by the rate of release of the GHGs-forcing stored in the oceans. The accompanying sea-level rise can continue for more than several centuries. Lastly, even the most aggressive CO(2) mitigation steps as envisioned now can only limit further additions to the committed warming, but not reduce the already committed GHGs warming of 2.4 degrees C.

On avoiding dangerous anthropogenic interference with the climate system: Formidable challenges ahead

PubMed Central

Ramanathan, V.; Feng, Y.

2008-01-01

The observed increase in the concentration of greenhouse gases (GHGs) since the preindustrial era has most likely committed the world to a warming of 2.4°C (1.4°C to 4.3°C) above the preindustrial surface temperatures. The committed warming is inferred from the most recent Intergovernmental Panel on Climate Change (IPCC) estimates of the greenhouse forcing and climate sensitivity. The estimated warming of 2.4°C is the equilibrium warming above preindustrial temperatures that the world will observe even if GHG concentrations are held fixed at their 2005 concentration levels but without any other anthropogenic forcing such as the cooling effect of aerosols. The range of 1.4°C to 4.3°C in the committed warming overlaps and surpasses the currently perceived threshold range of 1°C to 3°C for dangerous anthropogenic interference with many of the climate-tipping elements such as the summer arctic sea ice, Himalayan–Tibetan glaciers, and the Greenland Ice Sheet. IPCC models suggest that ≈25% (0.6°C) of the committed warming has been realized as of now. About 90% or more of the rest of the committed warming of 1.6°C will unfold during the 21st century, determined by the rate of the unmasking of the aerosol cooling effect by air pollution abatement laws and by the rate of release of the GHGs-forcing stored in the oceans. The accompanying sea-level rise can continue for more than several centuries. Lastly, even the most aggressive CO2 mitigation steps as envisioned now can only limit further additions to the committed warming, but not reduce the already committed GHGs warming of 2.4°C. PMID:18799733

Divergent global precipitation changes induced by natural versus anthropogenic forcing.

PubMed

Liu, Jian; Wang, Bin; Cane, Mark A; Yim, So-Young; Lee, June-Yi

2013-01-31

As a result of global warming, precipitation is likely to increase in high latitudes and the tropics and to decrease in already dry subtropical regions. The absolute magnitude and regional details of such changes, however, remain intensely debated. As is well known from El Niño studies, sea-surface-temperature gradients across the tropical Pacific Ocean can strongly influence global rainfall. Palaeoproxy evidence indicates that the difference between the warm west Pacific and the colder east Pacific increased in past periods when the Earth warmed as a result of increased solar radiation. In contrast, in most model projections of future greenhouse warming this gradient weakens. It has not been clear how to reconcile these two findings. Here we show in climate model simulations that the tropical Pacific sea-surface-temperature gradient increases when the warming is due to increased solar radiation and decreases when it is due to increased greenhouse-gas forcing. For the same global surface temperature increase the latter pattern produces less rainfall, notably over tropical land, which explains why in the model the late twentieth century is warmer than in the Medieval Warm Period (around AD 1000-1250) but precipitation is less. This difference is consistent with the global tropospheric energy budget, which requires a balance between the latent heat released in precipitation and radiative cooling. The tropospheric cooling is less for increased greenhouse gases, which add radiative absorbers to the troposphere, than for increased solar heating, which is concentrated at the Earth's surface. Thus warming due to increased greenhouse gases produces a climate signature different from that of warming due to solar radiation changes.

Century-Long Warming Trends in the Upper Water Column of Lake Tanganyika

PubMed Central

Kraemer, Benjamin M.; Hook, Simon; Huttula, Timo; Kotilainen, Pekka; O’Reilly, Catherine M.; Peltonen, Anu; Plisnier, Pierre-Denis; Sarvala, Jouko; Tamatamah, Rashid; Vadeboncoeur, Yvonne; Wehrli, Bernhard; McIntyre, Peter B.

2015-01-01

Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX86) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate change. Here, we use a comprehensive database of in situ temperature data from the top 100 meters of the water column that span the lake’s seasonal range and lateral extent to demonstrate that long-term temperature trends in Lake Tanganyika depend strongly on depth, season, and latitude. The observed spatiotemporal variation in surface warming rates accounts for small differences between warming rate estimates from in situ instruments and satellite data. However, after accounting for spatiotemporal variation in temperature and warming rates, the TEX86 paleolimnological proxy yields lower surface temperatures (1.46 °C lower on average) and faster warming rates (by a factor of three) than in situ measurements. Based on the ecology of Thaumarchaeota (the microbes whose biomolecules are involved with generating the TEX86 proxy), we offer a reinterpretation of the TEX86 data from Lake Tanganyika as the temperature of the low-oxygen zone, rather than of the lake surface temperature as has been suggested previously. Our analyses provide a thorough accounting of spatiotemporal variation in warming rates, offering strong evidence that thermal and ecological shifts observed in this massive tropical lake over the last century are robust and in step with global climate change. PMID:26147964

Warming and Nitrogen Addition Alter Photosynthetic Pigments, Sugars and Nutrients in a Temperate Meadow Ecosystem

PubMed Central

Zhang, Tao; Yang, Shaobo; Guo, Rui; Guo, Jixun

2016-01-01

Global warming and nitrogen (N) deposition have an important influence on terrestrial ecosystems; however, the influence of warming and N deposition on plant photosynthetic products and nutrient cycling in plants is not well understood. We examined the effects of 3 years of warming and N addition on the plant photosynthetic products, foliar chemistry and stoichiometric ratios of two dominant species, i.e., Leymus chinensis and Phragmites communis, in a temperate meadow in northeastern China. Warming significantly increased the chlorophyll content and soluble sugars in L. chinensis but had no impact on the carotenoid and fructose contents. N addition caused a significant increase in the carotenoid and fructose contents. Warming and N addition had little impact on the photosynthetic products of P. communis. Warming caused significant decreases in the N and phosphorus (P) concentrations and significantly increased the carbon (C):P and N:P ratios of L. chinensis, but not the C concentration or the C:N ratio. N addition significantly increased the N concentration, C:P and N:P ratios, but significantly reduced the C:N ratio of L. chinensis. Warming significantly increased P. communis C and P concentrations, and the C:N and C:P ratios, whereas N addition increased the C, N and P concentrations but had no impact on the stoichiometric variables. This study suggests that both warming and N addition have direct impacts on plant photosynthates and elemental stoichiometry, which may play a vital role in plant-mediated biogeochemical cycling in temperate meadow ecosystems. PMID:27171176

Global warming: Clouds cooled the Earth

NASA Astrophysics Data System (ADS)

Mauritsen, Thorsten

2016-12-01

The slow instrumental-record warming is consistent with lower-end climate sensitivity. Simulations and observations now show that changing sea surface temperature patterns could have affected cloudiness and thereby dampened the warming.

Contribution of tropical cyclones to abnormal sea surface temperature warming in the Yellow Sea in December 2004

NASA Astrophysics Data System (ADS)

Kim, Taekyun; Choo, Sung-Ho; Moon, Jae-Hong; Chang, Pil-Hun

2017-12-01

Unusual sea surface temperature (SST) warming occurred over the Yellow Sea (YS) in December 2004. To identify the causes of the abnormal SST warming, we conducted an analysis on atmospheric circulation anomalies induced by tropical cyclones (TCs) and their impacts on upper ocean characteristics using multiple datasets. With the analysis of various datasets, we explored a new aspect of the relationship between TC activity and SST. The results show that there is a significant link between TC activity over the Northwest Pacific (NWP) and SST in the YS. The integrated effect of consecutive TCs activity induces a large-scale atmospheric cyclonic circulation anomaly over the NWP and consequently anomalous easterly winds over the YS and East China Sea. The mechanism of the unusually warm SST in the YS can be explained by considering TCs acting as an important source of Ekman heat transport that results in substantial intrusion of relatively warm surface water into the YS interior. Furthermore, TC-related circulation anomalies contribute to the retention of the resulting warm SST anomalies in the entire YS.

Increased future ice discharge from Antarctica owing to higher snowfall

NASA Astrophysics Data System (ADS)

Winkelmann, Ricarda; Levermann, Anders; Martin, Maria A.; Frieler, Katja

2013-04-01

Anthropogenic climate change is likely to cause continuing global sea-level rise, but some processes within the Earth system may mitigate the magnitude of the projected effect. Regional and global climate models simulate enhanced snowfall over Antarctica, which would provide a direct offset of the future contribution to global sea level rise from cryospheric mass loss and ocean expansion. Uncertainties exist in modelled snowfall, but even larger uncertainties exist in the potential changes of dynamic ice discharge from Antarctica. Here we show that snowfall and discharge are not independent, but that future ice discharge will increase by up to three times as a result of additional snowfall under global warming. Our results, based on an ice-sheet model forced by climate simulations through to the end of 2500, show that the enhanced discharge effect exceeds the effect of surface warming as well as that of basal ice-shelf melting, and is due to the difference in surface elevation change caused by snowfall on grounded versus floating ice. Although different underlying forcings drive ice loss from basal melting versus increased snowfall, similar ice dynamical processes are nonetheless at work in both; therefore results are relatively independent of the specific representation of the transition zone. In an ensemble of simulations designed to capture ice-physics uncertainty, the additional dynamic ice loss along the coastline compensates between 30 and 65 per cent of the ice gain due to enhanced snowfall over the entire continent. This results in a dynamic ice loss of up to 1.25 metres in the year 2500 for the strongest warming scenario.

The role of climate change in regulating Arctic permafrost peatland hydrological and vegetation change over the last millennium

NASA Astrophysics Data System (ADS)

Zhang, Hui; Piilo, Sanna R.; Amesbury, Matthew J.; Charman, Dan J.; Gallego-Sala, Angela V.; Väliranta, Minna M.

2018-02-01

Climate warming has inevitable impacts on the vegetation and hydrological dynamics of high-latitude permafrost peatlands. These impacts in turn determine the role of these peatlands in the global biogeochemical cycle. Here, we used six active layer peat cores from four permafrost peatlands in Northeast European Russia and Finnish Lapland to investigate permafrost peatland dynamics over the last millennium. Testate amoeba and plant macrofossils were used as proxies for hydrological and vegetation changes. Our results show that during the Medieval Climate Anomaly (MCA), Russian sites experienced short-term permafrost thawing and this induced alternating dry-wet habitat changes eventually followed by desiccation. During the Little Ice Age (LIA) both sites generally supported dry-hummock habitats, at least partly driven by permafrost aggradation. However, proxy data suggest that occasionally, MCA habitat conditions were drier than during the LIA, implying that evapotranspiration may create important additional eco-hydrological feedback mechanisms under warm conditions. All sites showed a tendency towards dry conditions as inferred from both proxies starting either from ca. 100 years ago or in the past few decades after slight permafrost thawing, suggesting that recent warming has stimulated surface desiccation rather than deeper permafrost thawing. This study shows links between two important controls over hydrology and vegetation changes in high-latitude peatlands: direct temperature-induced surface layer response and deeper permafrost layer-related dynamics. These data provide important backgrounds for predictions of Arctic permafrost peatlands and related feedback mechanisms. Our results highlight the importance of increased evapotranspiration and thus provide an additional perspective to understanding of peatland-climate feedback mechanisms.

Responses of plant community composition and biomass production to warming and nitrogen deposition in a temperate meadow ecosystem.

PubMed

Zhang, Tao; Guo, Rui; Gao, Song; Guo, Jixun; Sun, Wei

2015-01-01

Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and biomass production are not well understood. A four-year field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and biomass production in a temperate meadow ecosystem in northeast China. Experimental warming had no significant effect on plant species richness, evenness, and diversity, while N addition highly reduced the species richness and diversity. Warming tended to reduce the importance value of graminoid species but increased the value of forbs, while N addition had the opposite effect. Warming tended to increase the belowground biomass, but had an opposite tendency to decrease the aboveground biomass. The influences of warming on aboveground production were dependent upon precipitation. Experimental warming had little effect on aboveground biomass in the years with higher precipitation, but significantly suppressed aboveground biomass in dry years. Our results suggest that warming had indirect effects on plant production via its effect on the water availability. Nitrogen addition significantly increased above- and below-ground production, suggesting that N is one of the most important limiting factors determining plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground biomass were also detected. Our observations revealed that environmental changes (warming and N deposition) play significant roles in regulating plant community composition and biomass production in temperate meadow steppe ecosystem in northeast China.

The Effects of Warming and Nitrogen Addition on Soil Nitrogen Cycling in a Temperate Grassland, Northeastern China

PubMed Central

Ma, Lin-Na; Lü, Xiao-Tao; Liu, Yang; Guo, Ji-Xun; Zhang, Nan-Yi; Yang, Jian-Qin; Wang, Ren-Zhong

2011-01-01

Background Both climate warming and atmospheric nitrogen (N) deposition are predicted to affect soil N cycling in terrestrial biomes over the next century. However, the interactive effects of warming and N deposition on soil N mineralization in temperate grasslands are poorly understood. Methodology/Principal Findings A field manipulation experiment was conducted to examine the effects of warming and N addition on soil N cycling in a temperate grassland of northeastern China from 2007 to 2009. Soil samples were incubated at a constant temperature and moisture, from samples collected in the field. The results showed that both warming and N addition significantly stimulated soil net N mineralization rate and net nitrification rate. Combined warming and N addition caused an interactive effect on N mineralization, which could be explained by the relative shift of soil microbial community structure because of fungal biomass increase and strong plant uptake of added N due to warming. Irrespective of strong intra- and inter-annual variations in soil N mineralization, the responses of N mineralization to warming and N addition did not change during the three growing seasons, suggesting independence of warming and N responses of N mineralization from precipitation variations in the temperate grassland. Conclusions/Significance Interactions between climate warming and N deposition on soil N cycling were significant. These findings will improve our understanding on the response of soil N cycling to the simultaneous climate change drivers in temperate grassland ecosystem. PMID:22096609

Numerical Study of the Role of Microphysical Latent Heating and Surface Heat Fluxes in a Severe Precipitation Event in the Warm Sector over Southern China

NASA Astrophysics Data System (ADS)

Yin, Jin-Fang; Wang, Dong-Hai; Liang, Zhao-Ming; Liu, Chong-Jian; Zhai, Guo-Qing; Wang, Hong

2018-02-01

Simulations of the severe precipitation event that occurred in the warm sector over southern China on 08 May 2014 are conducted using the Advanced Weather Research and Forecasting (WRF-ARWv3.5.1) model to investigate the roles of microphysical latent heating and surface heat fluxes during the severe precipitation processes. At first, observations from surface rain gauges and ground-based weather radars are used to evaluate the model outputs. Results show that the spatial distribution of 24-h accumulated precipitation is well reproduced, and the temporal and spatial distributions of the simulated radar reflectivity agree well with the observations. Then, several sensitive simulations are performed with the identical model configurations, except for different options in microphysical latent heating and surface heat fluxes. From the results, one of the significant findings is that the latent heating from warm rain microphysical processes heats the atmosphere in the initial phase of the precipitation and thus convective systems start by self-triggering and self-organizing, despite the fact that the environmental conditions are not favorable to the occurrence of precipitation event at the initial phase. In the case of the severe precipitation event over the warm sector, both warm and ice microphysical processes are active with the ice microphysics processes activated almost two hours later. According to the sensitive results, there is a very weak precipitation without heavy rainfall belt when microphysical latent heating is turned off. In terms of this precipitation event, the warm microphysics processes play significant roles on precipitation intensity, while the ice microphysics processes have effects on the spatial distribution of precipitation. Both surface sensible and latent heating have effects on the precipitation intensity and spatial distribution. By comparison, the surface sensible heating has a strong influence on the spatial distribution of precipitation, and the surface latent heating has only a slight impact on the precipitation intensity. The results indicate that microphysical latent heating might be an important factor for severe precipitation forecast in the warm sector over southern China. Surface sensible heating can have considerable influence on the precipitation spatial distribution and should not be neglected in the case of weak large-scale conditions with abundant water vapor in the warm sector.

Impacts of half a degree additional warming on the Asian summer monsoon rainfall characteristics

NASA Astrophysics Data System (ADS)

Lee, Donghyun; Min, Seung-Ki; Fischer, Erich; Shiogama, Hideo; Bethke, Ingo; Lierhammer, Ludwig; Scinocca, John F.

2018-04-01

This study investigates the impacts of global warming of 1.5 °C and 2.0 °C above pre-industrial conditions (Paris Agreement target temperatures) on the South Asian and East Asian monsoon rainfall using five atmospheric global climate models participating in the ‘Half a degree Additional warming, Prognosis and Projected Impacts’ (HAPPI) project. Mean and extreme precipitation is projected to increase under warming over the two monsoon regions, more strongly in the 2.0 °C warmer world. Moisture budget analysis shows that increases in evaporation and atmospheric moisture lead to the additional increases in mean precipitation with good inter-model agreement. Analysis of daily precipitation characteristics reveals that more-extreme precipitation will have larger increase in intensity and frequency responding to the half a degree additional warming, which is more clearly seen over the South Asian monsoon region, indicating non-linear scaling of precipitation extremes with temperature. Strong inter-model relationship between temperature and precipitation intensity further demonstrates that the increased moisture with warming (Clausius-Clapeyron relation) plays a critical role in the stronger intensification of more-extreme rainfall with warming. Results from CMIP5 coupled global climate models under a transient warming scenario confirm that half a degree additional warming would bring more frequent and stronger heavy precipitation events, exerting devastating impacts on the human and natural system over the Asian monsoon region.

Indo-Pacific climate during the decaying phase of the 2015/16 El Niño: role of southeast tropical Indian Ocean warming

NASA Astrophysics Data System (ADS)

Chen, Zesheng; Du, Yan; Wen, Zhiping; Wu, Renguang; Wang, Chunzai

2018-06-01

This study investigates the influence of southeast tropical Indian Ocean (SETIO) sea surface temperature (SST) warming on Indo-Pacific climate during the decaying phase of the 2015/16 El Niño by using observations and model experiments. The results show that the SETIO SST warming in spring 2016 enhanced local convection and forced a "C-shape" wind anomaly pattern in the lower troposphere. The "C-shape" wind anomaly pattern over the eastern tropical Indian Ocean consists of anomalous westerly flow south of the equator and anomalous easterly flow north of the equator. The anomalous easterly flow then extended eastward into the western North Pacific (WNP) and facilitates the development or the maintenance of an anomalous anticyclone over the South China Sea (SCS). Correspondingly, the eastern part of the Bay of Bengal, the SCS and the WNP suffered less rainfall. Such precipitation features and the associated "C-shape" wind anomaly pattern shifted northward about five latitudes in summer 2016. Additionally, the SETIO warming can induce local meridional circulation anomalies, which directly affect Indo-Pacific climate. Numerical model experiments further confirm that the SETIO SST warming plays an important role in modulating Indo-Pacific climate.

Warming early Mars with carbon dioxide clouds that scatter infrared radiation.

PubMed

Forget, F; Pierrehumbert, R T

1997-11-14

Geomorphic evidence that Mars was warm enough to support flowing water about 3.8 billion years ago presents a continuing enigma that cannot be explained by conventional greenhouse warming mechanisms. Model calculations show that the surface of early Mars could have been warmed through a scattering variant of the greenhouse effect, resulting from the ability of the carbon dioxide ice clouds to reflect the outgoing thermal radiation back to the surface. This process could also explain how Earth avoided an early irreversible glaciation and could extend the size of the habitable zone on extrasolar planets around stars.

Comparison of forced-air warming systems with lower body blankets using a copper manikin of the human body.

PubMed

Bräuer, A; English, M J M; Lorenz, N; Steinmetz, N; Perl, T; Braun, U; Weyland, W

2003-01-01

Forced-air warming has gained high acceptance as a measure for the prevention of intraoperative hypothermia. However, data on heat transfer with lower body blankets are not yet available. This study was conducted to determine the heat transfer efficacy of six complete lower body warming systems. Heat transfer of forced-air warmers can be described as follows:[1]Qdot;=h.DeltaT.A where Qdot; = heat transfer [W], h = heat exchange coefficient [W m-2 degrees C-1], DeltaT = temperature gradient between blanket and surface [ degrees C], A = covered area [m2]. We tested the following forced-air warmers in a previously validated copper manikin of the human body: (1) Bair Hugger and lower body blanket (Augustine Medical Inc., Eden Prairie, MN); (2) Thermacare and lower body blanket (Gaymar Industries, Orchard Park, NY); (3) WarmAir and lower body blanket (Cincinnati Sub-Zero Products, Cincinnati, OH); (4) Warm-Gard(R) and lower body blanket (Luis Gibeck AB, Upplands Väsby, Sweden); (5) Warm-Gard and reusable lower body blanket (Luis Gibeck AB); and (6) WarmTouch and lower body blanket (Mallinckrodt Medical Inc., St. Luis, MO). Heat flux and surface temperature were measured with 16 calibrated heat flux transducers. Blanket temperature was measured using 16 thermocouples. DeltaT was varied between -10 and +10 degrees C and h was determined by a linear regression analysis as the slope of DeltaT vs. heat flux. Mean DeltaT was determined for surface temperatures between 36 and 38 degrees C, because similar mean skin temperatures have been found in volunteers. The area covered by the blankets was estimated to be 0.54 m2. Heat transfer from the blanket to the manikin was different for surface temperatures between 36 degrees C and 38 degrees C. At a surface temperature of 36 degrees C the heat transfer was higher (between 13.4 W to 18.3 W) than at surface temperatures of 38 degrees C (8-11.5 W). The highest heat transfer was delivered by the Thermacare system (8.3-18.3 W), the lowest heat transfer was delivered by the Warm-Gard system with the single use blanket (8-13.4 W). The heat exchange coefficient varied between 12.5 W m-2 degrees C-1 and 30.8 W m-2 degrees C-1, mean DeltaT varied between 1.04 degrees C and 2.48 degrees C for surface temperatures of 36 degrees C and between 0.50 degrees C and 1.63 degrees C for surface temperatures of 38 degrees C. No relevant differences in heat transfer of lower body blankets were found between the different forced-air warming systems tested. Heat transfer was lower than heat transfer by upper body blankets tested in a previous study. However, forced-air warming systems with lower body blankets are still more effective than forced-air warming systems with upper body blankets in the prevention of perioperative hypothermia, because they cover a larger area of the body surface.

Modelling high Arctic deep permafrost temperature sensitivity in Northeast Greenland based on experimental and field observations

NASA Astrophysics Data System (ADS)

Rasmussen, Laura Helene; Zhang, Wenxin; Hollesen, Jørgen; Cable, Stefanie; Hvidtfeldt Christiansen, Hanne; Jansson, Per-Erik; Elberling, Bo

2017-04-01

Permafrost affected areas in Greenland are expected to experience a marked temperature increase within decades. Most studies have considered near-surface permafrost sensitivity, whereas permafrost temperatures below the depths of zero annual amplitude is less studied despite being closely related to changes in near-surface conditions, such as changes in active layer thermal properties, soil moisture and snow depth. In this study, we measured the sensitivity of thermal conductivity (TC) to gravimetric water content (GWC) in frozen and thawed permafrost sediments from fine-sandy and gravelly deltaic and fine-sandy alluvial deposits in the Zackenberg valley, NE Greenland. We further calibrated a coupled heat and water transfer model, the "CoupModel", for one central delta sediment site with average snow depth and further forced it with meteorology from a nearby delta sediment site with a topographic snow accumulation. With the calibrated model, we simulated deep permafrost thermal dynamics in four 20-year scenarios with changes in surface temperature and active layer (AL) soil moisture: a) 3 °C warming and AL water table at 0.5 m depth; b) 3 °C warming and AL water table at 0.1 m depth; c) 6 °C warming and AL water table at 0.5 m depth and d) 6 °C warming and AL water table at 0.1 m depth. Our results indicate that frozen sediments have higher TC than thawed sediments. All sediments show a positive linear relation between TC and soil moisture when frozen, and a logarithmic one when thawed. Gravelly delta sediments were highly sensitive, but never reached above 12 % GWC, indicating a field effect of water retention capacity. Alluvial sediments are less sensitive to soil moisture than deltaic (fine and coarse) sediments, indicating the importance of unfrozen water in frozen sediment. The deltaic site with snow accumulation had 1 °C higher mean annual ground temperature than the average snow depth site. Permafrost temperature at the depth of 18 m increased with 1.5 °C and 3.5 °C in the scenarios with 3 °C and 6 °C warming, respectively. Increasing the soil moisture had no important additional effect to warming, although an increase in thermal offset was indicated. We conclude that below-ground sediment properties affect the sensitivity of TC to GWC, that surface temperature changes can influence the deep permafrost within a short time scale, and that differences in snow depth affect surface temperatures. Sediment type and the type of precipitation should thus be considered when estimating future High Arctic deep permafrost sensitivity.

40 CFR Appendix H to Subpart G of... - Substitutes Subject to Use Restrictions and Unacceptable Substitutes, Effective May 28, 1999

Code of Federal Regulations, 2011 CFR

2011-07-01

.... Actual contributions to global warming depend upon the quantities emitted. See additional comments 1, 2.... Actual contributions to global warming depend upon the quantities of PFCs emitted. See additional.... Actual contributions to global warming depend upon the quantities of PFCs emitted. See additional...

Endurance of larch forest ecosystems in eastern Siberia under warming trends

NASA Astrophysics Data System (ADS)

Sato, H.; Iwahana, G.; Ohta, T.

2015-12-01

The larch (Larix spp.) forest in eastern Siberia is the world's largest coniferous forest. However, its existence depends on near-surface permafrost, which increases water availability for trees, and the boundary of the forest closely follows the permafrost zone. Therefore, the degradation of near-surface permafrost due to forecasted warming trends during the 21st century is expected to affect the larch forest in Siberia. However, predictions of how warming trends will affect this forest vary greatly, and many uncertainties remain about land-atmospheric interactions within the ecosystem. We developed an integrated land surface model to analyze how the Siberian larch forest will react to current warming trends. This model analyzed interactions between vegetation dynamics and thermo-hydrology and showed that, under climatic conditions predicted by the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathway (RCP) scenarios 2.6 and 8.5, annual larch net primary production (NPP) increased about 2 and 3 times, respectively, by the end of 21st century compared with that in the 20th century. Soil water content during larch growing season showed no obvious trend, even after decay of surface permafrost and accompanying sub-surface runoff. A sensitivity test showed that the forecasted warming and pluvial trends extended leafing days of larches and reduced water shortages during the growing season, thereby increasing productivity.

Decadal slowdown in global air temperature rise triggered by variability in the Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

England, Matthew H.

2015-04-01

Various explanations have been proposed for the recent slowdown in global surface air temperature (SAT) rise, either involving enhanced ocean heat uptake or reduced radiation reaching Earth's surface. Among the mechanisms postulated involving enhanced ocean heat uptake, past work has argued for both a Pacific and Atlantic origin, with additional contributions from the Southern Ocean. Here we examine the mechanisms driving 'hiatus' periods originating out of the Atlantic Ocean. We show that while Atlantic-driven hiatuses are entirely plausible and consistent with known climate feedbacks associated with variability in the Atlantic Meridional Overturning Circulation (AMOC), the present climate state is configured to enhance global-average SAT, not reduce it. We show that Atlantic hiatuses are instead characterised by anomalously cool fresh oceanic conditions in the North Atlantic, with the atmosphere advecting the cool temperature signature zonally. Compared to the 1980s and 1990s, however, the mean climate since 2001 has been characterised by a warm saline North Atlantic, suggesting the AMOC cannot be implicated as a direct driver of the current hiatus. We further discuss the impacts of a warm tropical Atlantic on the unprecedented trade wind acceleration in the Pacific Ocean, and propose that this is the main way that the Atlantic has contributed to the present "false pause" in global warming.

Melting icebergs to produce fresh water and mechanical energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Camirand, W.M.; Hautala, E.; Randall, J.M.

1981-10-20

Fresh water and mechanical energy are obtained from melting of icebergs. Warm surface seawater is contacted with a fluid, which is vaporized. The resulting vapor is used to generate mechanical energy and then is condensed by contacting it with cold melt water from the iceberg. The fluid is regenerated with a concomitant elevation in the temperature of the melt water. The warmer melt water is cycled to the body of the iceberg to facilitate its melting and produce additional cold melt water, which is apportioned as fresh water and water cycled to condense the aforesaid vapor. In an alternate embodimentmore » of the invention warm seawater is evaporated at reduced pressure. Mechanical energy is generated from the vapor, which is then condensed by direct and intimate contact with cold melt water from the iceberg. The resultant fresh water is a mixture of condensed vapor and melt water from the iceberg and has a temperature greater than the cold melt water. This fresh water mixture is contacted with the body of the iceberg to further melt it; part of the cold melt water is separated as fresh water and the remainder is cycled for use in condensing the vapor from the warm surface seawater.« less

Water- and Plant-Mediated Responses of Ecosystem Carbon Fluxes to Warming and Nitrogen Addition on the Songnen Grassland in Northeast China

PubMed Central

Jiang, Li; Guo, Rui; Zhu, Tingcheng; Niu, Xuedun; Guo, Jixun; Sun, Wei

2012-01-01

Background Understanding how grasslands are affected by a long-term increase in temperature is crucial to predict the future impact of global climate change on terrestrial ecosystems. Additionally, it is not clear how the effects of global warming on grassland productivity are going to be altered by increased N deposition and N addition. Methodology/Principal Findings In-situ canopy CO2 exchange rates were measured in a meadow steppe subjected to 4-year warming and nitrogen addition treatments. Warming treatment reduced net ecosystem CO2 exchange (NEE) and increased ecosystem respiration (ER); but had no significant impacts on gross ecosystem productivity (GEP). N addition increased NEE, ER and GEP. However, there were no significant interactions between N addition and warming. The variation of NEE during the four experimental years was correlated with soil water content, particularly during early spring, suggesting that water availability is a primary driver of carbon fluxes in the studied semi-arid grassland. Conclusion/Significance Ecosystem carbon fluxes in grassland ecosystems are sensitive to warming and N addition. In the studied water-limited grassland, both warming and N addition influence ecosystem carbon fluxes by affecting water availability, which is the primary driver in many arid and semiarid ecosystems. It remains unknown to what extent the long-term N addition would affect the turn-over of soil organic matter and the C sink size of this grassland. PMID:23028848

Air pollution, greenhouse gases and climate change: Global and regional perspectives

NASA Astrophysics Data System (ADS)

Ramanathan, V.; Feng, Y.

Greenhouse gases (GHGs) warm the surface and the atmosphere with significant implications for rainfall, retreat of glaciers and sea ice, sea level, among other factors. About 30 years ago, it was recognized that the increase in tropospheric ozone from air pollution (NO x, CO and others) is an important greenhouse forcing term. In addition, the recognition of chlorofluorocarbons (CFCs) on stratospheric ozone and its climate effects linked chemistry and climate strongly. What is less recognized, however, is a comparably major global problem dealing with air pollution. Until about ten years ago, air pollution was thought to be just an urban or a local problem. But new data have revealed that air pollution is transported across continents and ocean basins due to fast long-range transport, resulting in trans-oceanic and trans-continental plumes of atmospheric brown clouds (ABCs) containing sub micron size particles, i.e., aerosols. ABCs intercept sunlight by absorbing as well as reflecting it, both of which lead to a large surface dimming. The dimming effect is enhanced further because aerosols may nucleate more cloud droplets, which makes the clouds reflect more solar radiation. The dimming has a surface cooling effect and decreases evaporation of moisture from the surface, thus slows down the hydrological cycle. On the other hand, absorption of solar radiation by black carbon and some organics increase atmospheric heating and tend to amplify greenhouse warming of the atmosphere. ABCs are concentrated in regional and mega-city hot spots. Long-range transport from these hot spots causes widespread plumes over the adjacent oceans. Such a pattern of regionally concentrated surface dimming and atmospheric solar heating, accompanied by widespread dimming over the oceans, gives rise to large regional effects. Only during the last decade, we have begun to comprehend the surprisingly large regional impacts. In S. Asia and N. Africa, the large north-south gradient in the ABC dimming has altered both the north-south gradients in sea surface temperatures and land-ocean contrast in surface temperatures, which in turn slow down the monsoon circulation and decrease rainfall over the continents. On the other hand, heating by black carbon warms the atmosphere at elevated levels from 2 to 6 km, where most tropical glaciers are located, thus strengthening the effect of GHGs on retreat of snow packs and glaciers in the Hindu Kush-Himalaya-Tibetan glaciers. Globally, the surface cooling effect of ABCs may have masked as much 47% of the global warming by greenhouse gases, with an uncertainty range of 20-80%. This presents a dilemma since efforts to curb air pollution may unmask the ABC cooling effect and enhance the surface warming. Thus efforts to reduce GHGs and air pollution should be done under one common framework. The uncertainties in our understanding of the ABC effects are large, but we are discovering new ways in which human activities are changing the climate and the environment.

Role of Western Hemisphere Warm Pool in Rapid Climate Changes over the Western North Pacific

NASA Astrophysics Data System (ADS)

Kug, Jong-Seong; Park, Jae-Heung; An, Soon-Il

2017-04-01

Oceanic states over the western North Pacific (WNP), which is surrounded by heavily populated countries, are closely tied to the lives of the people in East Asia in regards to both climate and socioeconomics. As global warming continues, remarkable increases in sea surface temperature (SST) and sea surface height (SSH) have been observed in the WNP in recent decades. Here, we show that the SST increase in the western hemisphere warm pool (WHWP), which is the second largest warm pool on the globe, has contributed considerably to the rapid surface warming and sea level rise in the WNP via its remote teleconnection along the Pacific Intertropical Convergence Zone (ITCZ). State-of-the-art climate models strongly support the role of the WHWP not only on interannual time sales but also in long-term climate projections. We expect that understanding the processes initiated by the WHWP-SST could permit better forecasts of western North Pacific climate and the further development of the socioeconomics of East Asia.

Impact on short-lived climate forcers increases projected warming due to deforestation.

PubMed

Scott, C E; Monks, S A; Spracklen, D V; Arnold, S R; Forster, P M; Rap, A; Äijälä, M; Artaxo, P; Carslaw, K S; Chipperfield, M P; Ehn, M; Gilardoni, S; Heikkinen, L; Kulmala, M; Petäjä, T; Reddington, C L S; Rizzo, L V; Swietlicki, E; Vignati, E; Wilson, C

2018-01-11

The climate impact of deforestation depends on the relative strength of several biogeochemical and biogeophysical effects. In addition to affecting the exchange of carbon dioxide (CO 2 ) and moisture with the atmosphere and surface albedo, vegetation emits biogenic volatile organic compounds (BVOCs) that alter the formation of short-lived climate forcers (SLCFs), which include aerosol, ozone and methane. Here we show that a scenario of complete global deforestation results in a net positive radiative forcing (RF; 0.12 W m -2 ) from SLCFs, with the negative RF from decreases in ozone and methane concentrations partially offsetting the positive aerosol RF. Combining RFs due to CO 2 , surface albedo and SLCFs suggests that global deforestation could cause 0.8 K warming after 100 years, with SLCFs contributing 8% of the effect. However, deforestation as projected by the RCP8.5 scenario leads to zero net RF from SLCF, primarily due to nonlinearities in the aerosol indirect effect.

Responses of Plant Community Composition and Biomass Production to Warming and Nitrogen Deposition in a Temperate Meadow Ecosystem

PubMed Central

Gao, Song; Guo, Jixun; Sun, Wei

2015-01-01

Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and biomass production are not well understood. A four-year field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and biomass production in a temperate meadow ecosystem in northeast China. Experimental warming had no significant effect on plant species richness, evenness, and diversity, while N addition highly reduced the species richness and diversity. Warming tended to reduce the importance value of graminoid species but increased the value of forbs, while N addition had the opposite effect. Warming tended to increase the belowground biomass, but had an opposite tendency to decrease the aboveground biomass. The influences of warming on aboveground production were dependent upon precipitation. Experimental warming had little effect on aboveground biomass in the years with higher precipitation, but significantly suppressed aboveground biomass in dry years. Our results suggest that warming had indirect effects on plant production via its effect on the water availability. Nitrogen addition significantly increased above- and below-ground production, suggesting that N is one of the most important limiting factors determining plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground biomass were also detected. Our observations revealed that environmental changes (warming and N deposition) play significant roles in regulating plant community composition and biomass production in temperate meadow steppe ecosystem in northeast China. PMID:25874975

Understanding Arctic surface temperature differences in reanalyses

NASA Astrophysics Data System (ADS)

Cullather, R. I.; Zhao, B.; Shuman, C. A.; Nowicki, S.

2017-12-01

Reanalyses in the Arctic are widely used for model evaluation and for understanding contemporary climate change. Nevertheless, differences among reanalyses in fundamental meteorological variables including surface air temperature are large. For example, the 1980-2009 mean surface air temperature for the north polar cap (70°N-90°N) among global reanalyses span a range of 2.4 K, which approximates the average warming trend from these reanalyses over the 30-year period of 2.1 K. Understanding these differences requires evaluation over the three principal surface domains of the Arctic: glaciated land, the unglaciated terrestrial surface, and sea ice/ocean. An examination is conducted of contemporary global reanalyses of the ECMWF Interim project, NASA MERRA, MERRA-2, JRA-55, and NOAA CFSR using available in situ data and assessments of the surface energy budget. Overly-simplistic representations of the Greenland Ice Sheet surface are found to be associated with local warm air temperature biases in winter. A review of progress made in the development of the MERRA-2 land-ice representation is presented. Large uncertainty is also found in temperatures over the Arctic tundra and boreal forest zone. But a key focus of temperature differences for northern high latitudes is the Arctic Ocean. Near-surface air temperature differences over the Arctic Ocean are found to be related to discrepancies in sea ice and sea surface temperature boundary data, which are severely compromised in current reanalyses. Issues with the modeled representation of sea ice cover are an additional factor in reanalysis temperature trends. Differences in the representation of the surface energy budget among the various reanalyses are also reviewed.

Understanding Arctic Surface Temperature Differences in Reanalyses

NASA Technical Reports Server (NTRS)

Cullather, Richard; Zhao, Bin; Shuman, Christopher; Nowicki, Sophie

2017-01-01

Reanalyses in the Arctic are widely used for model evaluation and for understanding contemporary climate change. Nevertheless, differences among reanalyses in fundamental meteorological variables including surface air temperature are large. For example, the 1980-2009 mean surface air temperature for the north polar cap (70ÂdegN-90ÂdegN) among global reanalyses span a range of 2.4 K, which approximates the average warming trend from these reanalyses over the 30-year period of 2.1 K. Understanding these differences requires evaluation over the three principal surface domains of the Arctic: glaciated land, the unglaciated terrestrial surface, and sea ice/ocean. An examination is conducted of contemporary global reanalyses of the ECMWF Interim project, NASA MERRA, MERRA-2, JRA-55, and NOAA CFSR using available in situ data and assessments of the surface energy budget. Overly-simplistic representations of the Greenland Ice Sheet surface are found to be associated with local warm air temperature biases in winter. A review of progress made in the development of the MERRA-2 land-ice representation is presented. Large uncertainty is also found in temperatures over the Arctic tundra and boreal forest zone. But a key focus of temperature differences for northern high latitudes is the Arctic Ocean. Near-surface air temperature differences over the Arctic Ocean are found to be related to discrepancies in sea ice and sea surface temperature boundary data, which are severely compromised in current reanalyses. Issues with the modeled representation of sea ice cover are an additional factor in reanalysis temperature trends. Differences in the representation of the surface energy budget among the various reanalyses are also reviewed.

The Footprint of the Inter-decadal Pacific Oscillation in Indian Ocean Sea Surface Temperatures

NASA Astrophysics Data System (ADS)

Dong, Lu; Zhou, Tianjun; Dai, Aiguo; Song, Fengfei; Wu, Bo; Chen, Xiaolong

2016-02-01

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871-2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcings account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. The decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.

The Footprint of the Inter-decadal Pacific Oscillation in Indian Ocean Sea Surface Temperatures.

PubMed

Dong, Lu; Zhou, Tianjun; Dai, Aiguo; Song, Fengfei; Wu, Bo; Chen, Xiaolong

2016-02-17

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871-2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcings account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO's cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. The decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.

Enhanced Climatic Warming Over the Tibetan Plateau Due to Doubling CO2: A Model Study

NASA Technical Reports Server (NTRS)

Chen, Baode; Chao, Winston C.; Liu, Xiaodong; Lau, William K. M. (Technical Monitor)

2001-01-01

A number of studies have presented the evidences that surface climate change associated with global warming at high elevation sites shows more pronounced warming than at low elevations, i.e. an elevation dependency of climatic warming pointed out that snow-albedo feedback may be responsible for the excessive warming in the Swiss Alps. From an ensemble of climate change experiments of increasing greenhouse gases and aerosols using an air-sea coupled climate model, Eyre and Raw (1999) found a marked elevation dependency of the simulated surface screen temperature increase over the Rocky Mountains. Using almost all available instrumental records, Liu and Chen (2000) showed that the main portion of the Tibetan Plateau (TP) has experienced significant ground temperature warming since the middlebrows, especially in winter, and that there is a tendency for the warming trend to increase with elevation in the TP as well as its surrounding areas. In this paper, we will investigate the mechanism of elevation dependency of climatic warming in the TP by using a high-resolution regional climate model.

Delayed warming hiatus over the Tibetan Plateau

NASA Astrophysics Data System (ADS)

An, Wenling; Hou, Shugui; Hu, Yongyun; Wu, Shuangye

2017-03-01

A reduction in the warming rate for the global surface temperature since the late 1990s has attracted much attention and caused a great deal of controversy. During the same time period, however, most previous studies have reported enhanced warming over the Tibetan Plateau (TP). In this study we further examined the temperature trend of the TP and surrounding areas based on the homogenized temperature records for the period 1980-2014, we found that for the TP regions lower than 4000 m the warming rate has started to slow down since the late 1990s, a similar pattern consistent with the whole China and the global temperature trend. However, for the TP regions higher than 4000 m, this reduction in warming rate did not occur until the mid-2000s. This delayed warming hiatus could be related to changes in regional radiative, energy, and land surface processes in recent years.

Suppressed midlatitude summer atmospheric warming by Arctic sea ice loss during 1979-2012

NASA Astrophysics Data System (ADS)

Wu, Qigang; Cheng, Luyao; Chan, Duo; Yao, Yonghong; Hu, Haibo; Yao, Ying

2016-03-01

Since the 1980s, rapid Arctic warming, sea ice decline, and weakening summer circulation have coincided with an increasing number of extreme heat waves and other destructive weather events in the Northern Hemisphere (NH) midlatitudes in summer. Recent papers disagree about whether such high-impact events are related to Arctic warming and/or ice loss. Here we use atmospheric model ensemble simulations to attribute effects of sea ice loss and other factors on observed summer climate trends during 1979-2012. The ongoing greenhouse gas buildup and resulting sea surface temperature warming outside the Arctic explains nearly all land warming and a significant portion of observed weakening zonal winds in the NH midlatitudes. However, sea ice loss has induced a negative Arctic Oscillation(AO)-type circulation with significant summer surface and tropospheric cooling trends over large portions of the NH midlatitudes, which reduce the warming and might reduce the probability of regional severe hot summers.

Competition between global warming and an abrupt collapse of the AMOC in Earth's energy imbalance.

PubMed

Drijfhout, Sybren

2015-10-06

A collapse of the Atlantic Meridional Overturning Circulation (AMOC) leads to global cooling through fast feedbacks that selectively amplify the response in the Northern Hemisphere (NH). How such cooling competes with global warming has long been a topic for speculation, but was never addressed using a climate model. Here it is shown that global cooling due to a collapsing AMOC obliterates global warming for a period of 15-20 years. Thereafter, the global mean temperature trend is reversed and becomes similar to a simulation without an AMOC collapse. The resulting surface warming hiatus lasts for 40-50 years. Global warming and AMOC-induced NH cooling are governed by similar feedbacks, giving rise to a global net radiative imbalance of similar sign, although the former is associated with surface warming, the latter with cooling. Their footprints in outgoing longwave and absorbed shortwave radiation are very distinct, making attribution possible.

Changes in ENSO amplitude under climate warming and cooling

NASA Astrophysics Data System (ADS)

Wang, Yingying; Luo, Yiyong; Lu, Jian; Liu, Fukai

2018-05-01

The response of ENSO amplitude to climate warming and cooling is investigated using the Community Earth System Model (CESM), in which the warming and cooling scenarios are designed by adding heat fluxes of equal amplitude but opposite sign onto the ocean surface, respectively. Results show that the warming induces an increase of the ENSO amplitude but the cooling gives rise to a decrease of the ENSO amplitude, and these changes are robust in statistics. A mixed layer heat budget analysis finds that the increasing (decreasing) SST tendency under climate warming (cooling) is mainly due to an enhancement (weakening) of dynamical feedback processes over the equatorial Pacific, including zonal advective (ZA) feedback, meridional advective (MA) feedback, thermocline (TH) feedback, and Ekman (EK) feedback. As the climate warms, a wind anomaly of the same magnitude across the equatorial Pacific can induce a stronger zonal current change in the east (i.e., a stronger ZA feedback), which in turn produces a greater weakening of upwelling (i.e., a stronger EK feedback) and thus a larger thermocline change (i.e., a stronger TH feedback). In response to the climate warming, in addition, the MA feedback is also strengthened due to an enhancement of the meridional SST gradient around the equator resulting from a weakening of the subtropical cells (STCs). It should be noted that the weakened STCs itself has a negative contribution to the change of the MA feedback which, however, appears to be secondary. And vice versa for the cooling case. Bjerknes linear stability (BJ) index is also evaluated for the linear stability of ENSO, with remarkably larger (smaller) BJ index found for the warming (cooling) case.

Conservation Planning for Coral Reefs Accounting for Climate Warming Disturbances.

PubMed

Magris, Rafael A; Heron, Scott F; Pressey, Robert L

2015-01-01

Incorporating warming disturbances into the design of marine protected areas (MPAs) is fundamental to developing appropriate conservation actions that confer coral reef resilience. We propose an MPA design approach that includes spatially- and temporally-varying sea-surface temperature (SST) data, integrating both observed (1985-2009) and projected (2010-2099) time-series. We derived indices of acute (time under reduced ecosystem function following short-term events) and chronic thermal stress (rate of warming) and combined them to delineate thermal-stress regimes. Coral reefs located on the Brazilian coast were used as a case study because they are considered a conservation priority in the southwestern Atlantic Ocean. We show that all coral reef areas in Brazil have experienced and are projected to continue to experience chronic warming, while acute events are expected to increase in frequency and intensity. We formulated quantitative conservation objectives for regimes of thermal stress. Based on these objectives, we then evaluated if/how they are achieved in existing Brazilian MPAs and identified priority areas where additional protection would reinforce resilience. Our results show that, although the current system of MPAs incorporates locations within some of our thermal-stress regimes, historical and future thermal refugia along the central coast are completely unprotected. Our approach is applicable to other marine ecosystems and adds to previous marine planning for climate change in two ways: (i) by demonstrating how to spatially configure MPAs that meet conservation objectives for warming disturbance using spatially- and temporally-explicit data; and (ii) by strategically allocating different forms of spatial management (MPA types) intended to mitigate warming impacts and also enhance future resistance to climate warming.

Using radiative signatures to diagnose the cause of warming during the 2013-2014 Californian drought

NASA Astrophysics Data System (ADS)

Wolf, Sebastian; Yin, Dongqin; Roderick, Michael L.

2017-10-01

California recently experienced among the worst droughts of the last century, with exceptional precipitation deficits and co-occurring record high temperatures. The dry conditions caused severe water shortages in one of the economically most important agricultural regions of the US. It has recently been hypothesized that anthropogenic warming is increasing the likelihood of such extreme droughts in California, or more specifically, that warmer temperatures from the enhanced greenhouse effect intensify drought conditions. However, separating the cause and effect is difficult because the dry conditions lead to a reduction in evaporative cooling that contributes to the warming. Here we investigate and compare the forcing of long-term greenhouse-induced warming with the short-term warming during the 2013-2014 Californian drought. We use the concept of radiative signatures to investigate the source of the radiative perturbation during the drought, relate the signatures to expected changes due to anthropogenic warming, and assess the cause of warming based on observed changes in the surface energy balance compared to the period 2001-2012. We found that the recent meteorological drought based on precipitation deficits was characterised by an increase in incoming shortwave radiation coupled with a decline in incoming longwave radiation, which contributed to record warm temperatures. In contrast, climate models project that anthropogenic warming is accompanied by little change in incoming shortwave but a large increase in incoming longwave radiation. The warming during the drought was associated with increased incoming shortwave radiation in combination with reduced evaporative cooling from water deficits, which enhanced surface temperatures and sensible heat transfer to the atmosphere. Our analyses demonstrate that radiative signatures are a powerful tool to differentiate the source of perturbations in the surface energy balance at monthly to seasonal time scales.

Drivers of Antarctic sea-ice expansion and Southern Ocean surface cooling over the past four decades

NASA Astrophysics Data System (ADS)

Purich, Ariaan; England, Matthew

2017-04-01

Despite global warming, total Antarctic sea-ice coverage has increased overall during the past four decades. In contrast, the majority of CMIP5 models simulate a decline. In addition, Southern Ocean surface waters have largely cooled, in stark contrast to almost all historical CMIP5 simulations. Subantarctic Surface Waters have cooled and freshened while waters to the north of the Antarctic Circumpolar Current have warmed and increased in salinity. It remains unclear as to what extent the cooling and Antarctic sea-ice expansion is due to natural variability versus anthropogenic forcing; due for example to changes in the Southern Annular Mode (SAM). It is also unclear what the respective role of surface buoyancy fluxes is compared to internal ocean circulation changes, and what the implications are for longer-term climate change in the region. In this presentation we will outline three distinct drivers of recent Southern Ocean surface trends that have each made a significant contribution to regional cooling: (1) wind-driven surface cooling and sea-ice expansion due to shifted westerly winds, (2) teleconnections of decadal variability from the tropical Pacific, and (3) surface cooling and ice expansion due to large-scale Southern Ocean freshening, most likely driven by SAM-related precipitation trends over the open ocean. We will also outline the main reasons why climate models for the most part miss these Southern Ocean cooling trends, despite capturing overall trends in the SAM.

Soil Minerals Affect Extracellular Enzyme Activities in Cold and Warm Environments

NASA Astrophysics Data System (ADS)

Yang, Z.; Morin, M. M.; Graham, D. E.; Wullschleger, S. D.; Gu, B.

2017-12-01

Extracellular enzymes are mainly responsible for degrading and cycling soil organic matter (SOM) in both cold and warm terrestrial ecosystems. Minerals can play important roles in affecting soil enzyme activities, however, the interactions between enzyme and soil minerals remain poorly understood. In this study, we developed a model soil-enzyme system to examine the mineral effects on a hydrolytic enzyme (i.e., β-glucosidase) under both cold (4°C) and relatively warm (20 and 30°C) conditions. Minerals including iron oxides and clays (e.g., kaolinite and montmorillonite) were used to mimic different types of soils, and enzyme adsorption experiments were conducted to determine the enzyme interactions with different mineral surfaces. Time-series experiments were also carried out to measure enzymatic degradation of the organic substrates, such as cellobiose and indican. We observed that fractions of adsorbed enzyme and the hydrolytic activity were higher on iron oxides (e.g., hematite) compared to kaolinite and montmorillonite at given experimental conditions. The degradation of cellobiose was significantly faster than that of indican in the presence of minerals. We also found that the adsorption of enzyme was not dependent on the mineral surface areas, but was controlled by the mineral surface charge. In addition, temperature increase from 4 to 30°C enhanced mineral-assisted glucosidase hydrolysis by 2 to 4 fold, suggesting greater degradation under warmer environments. The present work demonstrates that the enzyme activity is influenced not only by the soil temperature but also by the surface chemistry of soil minerals. Our results highlight the need to consider the physical and chemical properties of minerals in biogeochemical models, which could provide a better prediction for enzyme-facilitated SOM transformations in terrestrial ecosystems.

Late Holocene SST and primary productivity variations in the northeastern Arabian Sea as a recorder for winter monsoon variability

NASA Astrophysics Data System (ADS)

Böll, Anna; Gaye, Birgit; Lückge, Andreas

2014-05-01

Variability in the oceanic environment of the Arabian Sea region is strongly influenced by the seasonal monsoon cycle of alternating wind directions. Strong south-westerly winds during the summer monsoon induce upwelling of nutrient rich waters along the coast off Somalia, Oman and southwest India, which result in high rates of primary production. In the northeastern Arabian Sea off Pakistan on the other hand, primary production and sea surface temperatures are linked to northeast monsoonal winds that cool the sea surface and drive convective mixing and high surface ocean productivity during the winter season. In this study, we analyzed alkenone-derived sea surface temperature (SST) variations and proxies of primary productivity (organic carbon and δ15N) in a well-laminated sediment core from the Pakistan continental margin to establish the first high-resolution record of winter monsoon variability for the late Holocene. Over the last 2400 years reconstructed SST in the northeastern Arabian Sea decreased whereas productivity increased, imaging a long-term trend of northeast monsoon strengthening in response to insolation-induced southward migration of the Intertropical Convergence Zone. The comparison of our winter monsoon record with records of summer monsoon intensity suggests that summer and winter monsoon strength was essentially anti-correlated over the late Holocene throughout the Asian monsoon system. In addition, SST variations recorded off Pakistan match very well with Northern Hemisphere temperature records supporting the growing body of evidence that Asian climate is linked to Northern Hemisphere climate change. It reveals a consistent pattern of increased summer monsoon activity in the northeastern Arabian Sea during northern hemispheric warm periods (Medieval Warm Period, Roman Warm Period) and strengthened winter monsoon activity during hemispheric colder periods (Little Ice Age).

Effects of urban land-use change in East China on the East Asian summer monsoon based on the CAM5.1 model

NASA Astrophysics Data System (ADS)

Ma, Hongyun; Jiang, Zhihong; Song, Jie; Dai, Aiguo; Yang, Xiuqun; Huo, Fei

2016-05-01

The effects of urban land-use change in East China on the East Asian summer monsoon (EASM) are investigated using a Community Atmosphere Model Version 5.1. The results show that the urban land-use change in East China causes spatially-varying changes in surface net radiation and heat fluxes, atmospheric circulation, and water budgets. It results in significant surface warming (cooling) and precipitation decrease (increase) in a large region north (south) of 30°N. Urban expansion agglomerated in (29°-41°N, 110°-122°E) alters the surface energy budget and warms the surface, resulting in strengthened southwesterly airflow south of 25°N and increased convergence below the mid-troposphere between 20° and 30°N. A concomitant northward downdraft associated with the increased convection generates an anomalous high pressure north of 30°N. Meanwhile, the downdraft not only produces adiabatic warming but also inhibits the dynamic condition for precipitation formation. The anomalous high pressure formed in North China prevents the southwesterly airflow from advancing northward, leading to increase the convergence and precipitation in South China. These changes reduce the meridional temperature gradient in the mid-lower troposphere and weaken the westerly airflow near 30°N. In addition, horizontal transport of vorticity north of 35°N weakens significantly, which leads to an anomalous barotropic structure of anticyclonic there. As a result, the anomalous anticyclonic circulation and descent north of 30°N are strengthened. At the same time, the anomalous cyclonic circulation and ascent south of 30°N are enhanced. These process induced by the thermal state changes due to urbanization weakens the EASM.

Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year.

PubMed

Steig, Eric J; Schneider, David P; Rutherford, Scott D; Mann, Michael E; Comiso, Josefino C; Shindell, Drew T

2009-01-22

Assessments of Antarctic temperature change have emphasized the contrast between strong warming of the Antarctic Peninsula and slight cooling of the Antarctic continental interior in recent decades. This pattern of temperature change has been attributed to the increased strength of the circumpolar westerlies, largely in response to changes in stratospheric ozone. This picture, however, is substantially incomplete owing to the sparseness and short duration of the observations. Here we show that significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica, an area of warming much larger than previously reported. West Antarctic warming exceeds 0.1 degrees C per decade over the past 50 years, and is strongest in winter and spring. Although this is partly offset by autumn cooling in East Antarctica, the continent-wide average near-surface temperature trend is positive. Simulations using a general circulation model reproduce the essential features of the spatial pattern and the long-term trend, and we suggest that neither can be attributed directly to increases in the strength of the westerlies. Instead, regional changes in atmospheric circulation and associated changes in sea surface temperature and sea ice are required to explain the enhanced warming in West Antarctica.

Formation of well-mixed warm water column in central Bohai Sea during summer: Role of high-frequency atmospheric forcing

NASA Astrophysics Data System (ADS)

Ma, Weiwei; Wan, Xiuquan; Wang, Zhankun; Liu, Yulong; Wan, Kai

2017-12-01

The influence of high-frequency atmospheric forcing on the formation of a well-mixed summer warm water column in the central Bohai Sea is investigated comparing model simulations driven by daily surface forcing and those using monthly forcing data. In the absence of high-frequency atmospheric forcing, numerical simulations have repeatedly failed to reproduce this vertically uniform column of warm water measured over the past 35 years. However, high-frequency surface forcing is found to strongly influence the structure and distribution of the well-mixed warm water column, and simulations are in good agreement with observations. Results show that high frequency forcing enhances vertical mixing over the central bank, intensifies downward heat transport, and homogenizes the water column to form the Bohai central warm column. Evidence presented shows that high frequency forcing plays a dominant role in the formation of the well-mixed warm water column in summer, even without the effects of tidal and surface wave mixing. The present study thus provides a practical and rational way of further improving the performance of oceanic simulations in the Bohai Sea and can be used to adjust parameterization schemes of ocean models.

Evaluating Arctic warming mechanisms in CMIP5 models

NASA Astrophysics Data System (ADS)

Franzke, Christian L. E.; Lee, Sukyoung; Feldstein, Steven B.

2017-05-01

Arctic warming is one of the most striking signals of global warming. The Arctic is one of the fastest warming regions on Earth and constitutes, thus, a good test bed to evaluate the ability of climate models to reproduce the physics and dynamics involved in Arctic warming. Different physical and dynamical mechanisms have been proposed to explain Arctic amplification. These mechanisms include the surface albedo feedback and poleward sensible and latent heat transport processes. During the winter season when Arctic amplification is most pronounced, the first mechanism relies on an enhancement in upward surface heat flux, while the second mechanism does not. In these mechanisms, it has been proposed that downward infrared radiation (IR) plays a role to a varying degree. Here, we show that the current generation of CMIP5 climate models all reproduce Arctic warming and there are high pattern correlations—typically greater than 0.9—between the surface air temperature (SAT) trend and the downward IR trend. However, we find that there are two groups of CMIP5 models: one with small pattern correlations between the Arctic SAT trend and the surface vertical heat flux trend (Group 1), and the other with large correlations (Group 2) between the same two variables. The Group 1 models exhibit higher pattern correlations between Arctic SAT and 500 hPa geopotential height trends, than do the Group 2 models. These findings suggest that Arctic warming in Group 1 models is more closely related to changes in the large-scale atmospheric circulation, whereas in Group 2, the albedo feedback effect plays a more important role. Interestingly, while Group 1 models have a warm or weak bias in their Arctic SAT, Group 2 models show large cold biases. This stark difference in model bias leads us to hypothesize that for a given model, the dominant Arctic warming mechanism and trend may be dependent on the bias of the model mean state.

Effects of experimental warming and elevated CO2 on surface methane and CO­2 fluxes from a boreal black spruce peatland

NASA Astrophysics Data System (ADS)

Gill, A. L.; Finzi, A.; Hsieh, I. F.; Giasson, M. A.

2016-12-01

High latitude peatlands represent a major terrestrial carbon store sensitive to climate change, as well as a globally significant methane source. While elevated atmospheric carbon dioxide concentrations and warming temperatures may increase peat respiration and C losses to the atmosphere, reductions in peatland water tables associated with increased growing season evapotranspiration may alter the nature of trace gas emission and increase peat C losses as CO2 relative to methane (CH4). As CH4 is a greenhouse gas with twenty times the warming potential of CO2, it is critical to understand how surface fluxes of CO2 and CH4 will be influenced by factors associated with global climate change. We used automated soil respiration chambers to assess the influence of elevated atmospheric CO2 and whole ecosystem warming on peatland CH4 and CO2 fluxes at the SPRUCE (Spruce and Peatland Responses Under Climatic and Environmental Change) Experiment in northern Minnesota. Here we report soil iCO2 and iCH4 flux responses to the first year of belowground warming and the first season of whole ecosystem warming and elevated CO2 treatments. We find that peat methane fluxes are more sensitive to warming treatments than peat CO2 fluxes, particularly in hollow peat microforms. Surface CO2:CH4 flux ratios decreased across warming treatments, suggesting that the temperature sensitivity of methane production overshadows the effect of peat drying and surface aeration in the short term. δ13C of the emitted methane was more depleted in the early and late growing season, indicating a transition from hydrogenotrophic to acetoclastic methanogenesis during periods of high photosynthetic input. The measurement record demonstrates that belowground warming has measureable impacts on the nature of peat greenhouse gas emission within one year of treatment.

Climate-induced warming of lakes can be either amplified or suppressed by trends in water clarity

USGS Publications Warehouse

Rose, Kevin C.; Winslow, Luke A.; Read, Jordan S.; Hansen, Gretchen J. A.

2016-01-01

Climate change is rapidly warming aquatic ecosystems including lakes and reservoirs. However, variability in lake characteristics can modulate how lakes respond to climate. Water clarity is especially important both because it influences the depth range over which heat is absorbed, and because it is changing in many lakes. Here, we show that simulated long-term water clarity trends influence how both surface and bottom water temperatures of lakes and reservoirs respond to climate change. Clarity changes can either amplify or suppress climate-induced warming, depending on lake depth and the direction of clarity change. Using a process-based model to simulate 1894 north temperate lakes from 1979 to 2012, we show that a scenario of decreasing clarity at a conservative yet widely observed rate of 0.92% yr−1 warmed surface waters and cooled bottom waters at rates comparable in magnitude to climate-induced warming. For lakes deeper than 6.5 m, decreasing clarity was sufficient to fully offset the effects of climate-induced warming on median whole-lake mean temperatures. Conversely, a scenario increasing clarity at the same rate cooled surface waters and warmed bottom waters relative to baseline warming rates. Furthermore, in 43% of lakes, increasing clarity more than doubled baseline bottom temperature warming rates. Long-term empirical observations of water temperature in lakes with and without clarity trends support these simulation results. Together, these results demonstrate that water clarity trends may be as important as rising air temperatures in determining how waterbodies respond to climate change.

Climate Effect of Greenhouse Gas: Warming or Cooling is Determined by Temperature Gradient

NASA Astrophysics Data System (ADS)

Shia, R.

2011-12-01

The instantaneous radiative forcing (IRF) at the top of the atmosphere (ToA) is the initial change of the total energy in the climate system when the concentration of greenhouse gas (GHG) increases. In my previous presentation at the 2010 Fall AGU meeting (A11J-02, "Mechanism of Radiative Forcing of Greenhouse Gas its Implication to the Global Warming"), it was demonstrated that IRF at TOA is generated by moving up of the emission weighting function. Thus, the temperature gradient plays a critical role in determining the climate effect of GHG. In this presentation the change of the outgoing infrared radiation flux at ToA is studied from a perturbation point of view. After the cancellation between the changes in the outgoing radiation flux from the surface emission and from the reemission of the atmosphere, the derivative of the outgoing flux to the concentration of GHG is found to be proportional to the temperature gradients below the level where the concentration of GHG changes. Therefore, the greenhouse gas contribute only to the magnitude of the radiative forcing, the temperature gradients decide the direction of the radiative forcing, i.e. warming or cooling, in addition to contributing to its magnitude. In response to the question "Does the negative IRF at ToA lead to the surface cooling or it only cools the upper part of the atmosphere?" the Eddington grey radiative equilibrium model is modified to simulate different scenarios. The original model has been used to illustrate the warming effect of GHG in textbooks of the atmospheric physics. It is modified by adding source terms from the absorption of the solar flux and the internal energy exchange in the atmosphere. In two cases the modified model generates atmospheres with a large and warm stratosphere and negative IRF at ToA when GHG increases by 25%. This negative radiative forcing can lead to the cooling of the atmosphere all the way down to the surface. The implications of the cooling effect of GHG to the climate change, including paleoclimatology and the prerequests for climate models to include cooling effect of GHG properly are discussed.

Seasonal responses of soil respiration to warming and nitrogen addition in a semi-arid alfalfa-pasture of the Loess Plateau, China.

PubMed

Fang, Chao; Ye, Jian-Sheng; Gong, Yanhong; Pei, Jiuying; Yuan, Ziqiang; Xie, Chan; Zhu, Yusi; Yu, Yueyuan

2017-07-15

Responses of soil respiration (R s ) to increasing nitrogen (N) deposition and warming will have far-reaching influences on global carbon (C) cycling. However, the seasonal (growing and non-growing seasons) difference of R s responses to warming and N deposition has rarely been investigated. We conducted a field manipulative experiment in a semi-arid alfalfa-pasture of northwest China to evaluate the response of R s to nitrogen addition and warming from March 2014 to March 2016. Open-top chambers were used to elevate temperature and N was enriched at a rate of 4.42g m -2 yr -1 with NH 4 NO 3 . Results showed that (1) N addition increased R s by 14% over the two-year period; and (2) warming stimulated R s by 15% in the non-growing season, while inhibited it by 5% in the growing season, which can be explained by decreased plant coverage and soil water. The main effect of N addition did not change with time, but that of warming changed with time, with the stronger inhibition observed in the dry year. When N addition and warming were combined, an antagonistic effect was observed in the growing season, whereas a synergism was observed in the non-growing season. Overall, warming and N addition did not affect the Q10 values over the two-year period, but these treatments significantly increased the Q10 values in the growing season compared with the control treatment. In comparison, combined warming and nitrogen addition significantly reduced the Q10 values compared with the single factor treatment. These results suggest that the negative indirect effect of warming-induced water stress overrides the positive direct effect of warming on R s . Our results also imply the necessity of considering the different R s responses in the growing and non-growing seasons to climate change to accurately evaluate the carbon cycle in the arid and semi-arid regions. Copyright © 2017 Elsevier B.V. All rights reserved.

Bathymetric controls on Pliocene North Atlantic and Arctic sea surface temperature and deepwater production

USGS Publications Warehouse

Robinson, M.M.; Valdes, P.J.; Haywood, A.M.; Dowsett, H.J.; Hill, D.J.; Jones, S.M.

2011-01-01

The mid-Pliocene warm period (MPWP; ~. 3.3 to 3.0. Ma) is the most recent interval in Earth's history in which global temperatures reached and remained at levels similar to those projected for the near future. The distribution of global warmth, however, was different than today in that the high latitudes warmed more than the tropics. Multiple temperature proxies indicate significant sea surface warming in the North Atlantic and Arctic Oceans during the MPWP, but predictions from a fully coupled ocean-atmosphere model (HadCM3) have so far been unable to fully predict the large scale of sea surface warming in the high latitudes. If climate proxies accurately represent Pliocene conditions, and if no weakness exists in the physics of the model, then model boundary conditions may be in error. Here we alter a single boundary condition (bathymetry) to examine if Pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of North Atlantic Ocean ridges. We find an increase in both Arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened Greenland-Scotland Ridge. These results offer both a mechanism for the warming in the North Atlantic and Arctic Oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of Pliocene northern North Atlantic and Arctic Ocean conditions. Determining the causes of Pliocene warmth remains critical to fully understanding comparisons of the Pliocene warm period to possible future climate change scenarios. ?? 2011.

Was Early Mars Warmed by CH4?

NASA Astrophysics Data System (ADS)

Justh, H. L.; Kasting, J. F.

2001-12-01

Images from the Mariner, Viking and Mars Global Surveyor missions have shown geologic features on the Martian surface that seem to indicate an earlier period of hydrologic activity. Many researchers have suggested that the early Martian climate was more Earth-like with a Ts of 273 K or higher. The presence of liquid water would require a greenhouse effect much larger than needed at present since S0 is 25% lower 3.8 billion years ago when the channels are thought to have formed. Research into the effects of CO2 clouds upon the climate of early Mars have yielded results that would not effectively warm the surface to the temperature needed to account for the presence of liquid water. Forget and Pierrehumbert (Science, 1997) showed that large crystals of CO2 ice in clouds that form in the upper troposphere would produce a strong warming effect. Obtaining mean surface temperatures above 273 K would require 100% cloud cover, a condition that is unrealistic for early Mars. It has also been shown that any reduction in cloud cover makes it difficult to achieve warm Martian surface temperatures except at high pressures. CO2 clouds could also cool the Martian surface if they were low and optically thick. CO2 ice may be hard to nucleate, leading to the formation of very large particles (Glandorf, private communication). CH4 has been suggested as an important greenhouse gas on the early Earth. This has led us to look at CH4 as a potential solution to the early Mars climate issue. To investigate the possible warming effect of CH4, we utilized a modified, one-dimensional, radiative-convective climate model that has been used in previous studies of the early Martian climate. New calculations of the effects of CH4 upon the early Martian climate will be presented. The use of CH4 to warm the surface of early Mars does not necessarily imply the presence of life on Mars. Abiotic sources of CH4, such as serpentinization of ultramafic rocks, could supply the concentrations needed to warm the surface.

Enhanced greenhouse gas emissions from the Arctic with experimental warming

NASA Astrophysics Data System (ADS)

Voigt, Carolina; Lamprecht, Richard E.; Marushchak, Maija E.; Lind, Saara E.; Novakovskiy, Alexander; Aurela, Mika; Martikainen, Pertti J.; Biasi, Christina

2017-04-01

Temperatures in the Arctic are projected to increase more rapidly than in lower latitudes. With temperature being a key factor for regulating biogeochemical processes in ecosystems, even a subtle temperature increase might promote the release of greenhouse gases (GHGs) to the atmosphere. Usually, carbon dioxide (CO2) and methane (CH4) are the GHGs dominating the climatic impact of tundra. However, bare, patterned ground features in the Arctic have recently been identified as hot spots for nitrous oxide (N2O). N2O is a potent greenhouse gas, which is almost 300 times more effective in its global warming potential than CO2; but studies on arctic N2O fluxes are rare. In this study we examined the impact of temperature increase on the seasonal GHG balance of all three important GHGs (CO2, CH4 and N2O) from three tundra surface types (vegetated peat soils, unvegetated peat soils, upland mineral soils) in the Russian Arctic (67˚ 03' N 62˚ 55' E), during the course of two growing seasons. We deployed open-top chambers (OTCs), inducing air and soil surface warming, thus mimicking predicted warming scenarios. We combined detailed CO2, CH4 and N2O flux studies with concentration measurements of these gases within the soil profile down to the active layer-permafrost interface, and complemented these GHG measurements with detailed soil nutrient (nitrate and ammonium) and dissolved organic carbon (DOC) measurements in the soil pore water profile. In our study, gentle air warming (˜1.0 ˚ C) increased the seasonal GHG release of all dominant surface types: the GHG budget of vegetated peat and mineral soils, which together cover more than 80 % of the land area in our study region, shifted from a sink to a source of -300 to 144 g CO2-eq m-2 and from -198 to 105 g CO2-eq m-2, respectively. While the positive warming response was governed by CO2, we provide here the first in situ evidence that warming increases arctic N2O emissions: Warming did not only enhance N2O emissions from the known arctic N2O hot spots (bare peat soils; maximum seasonal release with warming: 87 mg N2O m-2), but also from the vegetated peat surfaces, not emitting N2O under present climate. These surfaces showed signs of a hampered plant growth, leading to reduced soil N uptake with warming, indicating that plants are regulating arctic N2O emissions. The warming treatment was limited to temperature of air and upper soil surface, and did not alter thaw depth. Nonetheless, we observed a clear increase of all three GHGs deep in the soil profile, and attribute this to downward leaching of labile organic substances from the surface soil and/or plants, fueling microbial activity at depth. Our study thus highlights the tight interlinkage between the surface soil, vegetation, and deeper soil layers, which could lead to losses of all three GHGs, including N2O, with subtle temperature increase. We therefore emphasize that indirect effects caused by warming, such as leaching processes, as well as arctic N2O emissions, need to be taken into account when attempting to project feedbacks between the arctic and the global climate system.

Coastal warming and wind-driven upwelling: A global analysis.

PubMed

Varela, Rubén; Lima, Fernando P; Seabra, Rui; Meneghesso, Claudia; Gómez-Gesteira, Moncho

2018-10-15

Long-term sea surface temperature (SST) warming trends are far from being homogeneous, especially when coastal and ocean locations are compared. Using data from NOAA's AVHRR OISST, we have analyzed sea surface temperature trends over the period 1982-2015 at around 3500 worldwide coastal points and their oceanic counterparts with a spatial resolution of 0.25 arc-degrees. Significant warming was observed at most locations although with important differences between oceanic and coastal points. This is especially patent for upwelling regions, where 92% of the coastal locations showed lower warming trends than at neighboring ocean locations. This result strongly suggests that upwelling has the potential to buffer the effects of global warming nearshore, with wide oceanographic, climatic, and biogeographic implications. Copyright © 2018 Elsevier B.V. All rights reserved.

Stratospheric ozone changes under solar geoengineering: implications for UV exposure and air quality

NASA Astrophysics Data System (ADS)

Nowack, Peer Johannes; Abraham, Nathan Luke; Braesicke, Peter; Pyle, John Adrian

2016-03-01

Various forms of geoengineering have been proposed to counter anthropogenic climate change. Methods which aim to modify the Earth's energy balance by reducing insolation are often subsumed under the term solar radiation management (SRM). Here, we present results of a standard SRM modelling experiment in which the incoming solar irradiance is reduced to offset the global mean warming induced by a quadrupling of atmospheric carbon dioxide. For the first time in an atmosphere-ocean coupled climate model, we include atmospheric composition feedbacks for this experiment. While the SRM scheme considered here could offset greenhouse gas induced global mean surface warming, it leads to important changes in atmospheric composition. We find large stratospheric ozone increases that induce significant reductions in surface UV-B irradiance, which would have implications for vitamin D production. In addition, the higher stratospheric ozone levels lead to decreased ozone photolysis in the troposphere. In combination with lower atmospheric specific humidity under SRM, this results in overall surface ozone concentration increases in the idealized G1 experiment. Both UV-B and surface ozone changes are important for human health. We therefore highlight that both stratospheric and tropospheric ozone changes must be considered in the assessment of any SRM scheme, due to their important roles in regulating UV exposure and air quality.

Evaluation of NASA GEOS-ADAS Modeled Diurnal Warming Through Comparisons to SEVIRI and AMSR2 SST Observations

NASA Astrophysics Data System (ADS)

Gentemann, C. L.; Akella, S.

2018-02-01

An analysis of the ocean skin Sea Surface Temperature (SST) has been included in the Goddard Earth Observing System (GEOS) - Atmospheric Data Assimilation System (ADAS), Version 5 (GEOS-ADAS). This analysis is based on the GEOS atmospheric general circulation model (AGCM) that simulates near-surface diurnal warming and cool skin effects. Analysis for the skin SST is performed along with the atmospheric state, including Advanced Very High Resolution Radiometer (AVHRR) satellite radiance observations as part of the data assimilation system. One month (September, 2015) of GEOS-ADAS SSTs were compared to collocated satellite Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and Advanced Microwave Scanning Radiometer 2 (AMSR2) SSTs to examine how the GEOS-ADAS diurnal warming compares to the satellite measured warming. The spatial distribution of warming compares well to the satellite observed distributions. Specific diurnal events are analyzed to examine variability within a single day. The dependence of diurnal warming on wind speed, time of day, and daily average insolation is also examined. Overall the magnitude of GEOS-ADAS warming is similar to the warming inferred from satellite retrievals, but several weaknesses in the GEOS-AGCM simulated diurnal warming are identified and directly related back to specific features in the formulation of the diurnal warming model.

Seasonality of change: Summer warming rates do not fully represent effects of climate change on lake temperatures

USGS Publications Warehouse

Winslow, Luke; Read, Jordan S.; Hansen, Gretchen J. A.; Rose, Kevin C.; Robertson, Dale M.

2017-01-01

Responses in lake temperatures to climate warming have primarily been characterized using seasonal metrics of surface-water temperatures such as summertime or stratified period average temperatures. However, climate warming may not affect water temperatures equally across seasons or depths. We analyzed a long-term dataset (1981–2015) of biweekly water temperature data in six temperate lakes in Wisconsin, U.S.A. to understand (1) variability in monthly rates of surface- and deep-water warming, (2) how those rates compared to summertime average trends, and (3) if monthly heterogeneity in water temperature trends can be predicted by heterogeneity in air temperature trends. Monthly surface-water temperature warming rates varied across the open-water season, ranging from 0.013 in August to 0.073°C yr−1 in September (standard deviation [SD]: 0.025°C yr−1). Deep-water trends during summer varied less among months (SD: 0.006°C yr−1), but varied broadly among lakes (–0.056°C yr−1 to 0.035°C yr−1, SD: 0.034°C yr−1). Trends in monthly surface-water temperatures were well correlated with air temperature trends, suggesting monthly air temperature trends, for which data exist at broad scales, may be a proxy for seasonal patterns in surface-water temperature trends during the open water season in lakes similar to those studied here. Seasonally variable warming has broad implications for how ecological processes respond to climate change, because phenological events such as fish spawning and phytoplankton succession respond to specific, seasonal temperature cues.

Projected warming portends seasonal shifts of stream temperatures in the Crown of the Continent Ecosystem, USA and Canada

USGS Publications Warehouse

Jones, Leslie A.; Muhlfeld, Clint C.; Marshall, Lucy A.

2017-01-01

Climate warming is expected to increase stream temperatures in mountainous regions of western North America, yet the degree to which future climate change may influence seasonal patterns of stream temperature is uncertain. In this study, a spatially explicit statistical model framework was integrated with empirical stream temperature data (approximately four million bi-hourly recordings) and high-resolution climate and land surface data to estimate monthly stream temperatures and potential change under future climate scenarios in the Crown of the Continent Ecosystem, USA and Canada (72,000 km2). Moderate and extreme warming scenarios forecast increasing stream temperatures during spring, summer, and fall, with the largest increases predicted during summer (July, August, and September). Additionally, thermal regimes characteristic of current August temperatures, the warmest month of the year, may be exceeded during July and September, suggesting an earlier and extended duration of warm summer stream temperatures. Models estimate that the largest magnitude of temperature warming relative to current conditions may be observed during the shoulder months of winter (April and November). Summer stream temperature warming is likely to be most pronounced in glacial-fed streams where models predict the largest magnitude (> 50%) of change due to the loss of alpine glaciers. We provide the first broad-scale analysis of seasonal climate effects on spatiotemporal patterns of stream temperature in the Crown of the Continent Ecosystem for better understanding climate change impacts on freshwater habitats and guiding conservation and climate adaptation strategies.

Asymmetric Response of the Equatorial Pacific SST to Climate Warming and Cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Fukai; Luo, Yiyong; Lu, Jian

The response of the equatorial Pacific Ocean to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model (CESM). Results show a strong asymmetry in SST changes. In the eastern equatorial Pacific (EEP), the warming responding to the positive forcing exceeds the cooling to the negative forcing; while in the western equatorial Pacific (WEP), it is the other way around and the cooling surpasses the warming. This leads to a zonal dipole asymmetric structure, with positive values in the east and negative values in the west. A surface heat budget analysis suggests that themore » SST asymmetry is mainly resulted from the oceanic horizontal advection and vertical entrainment, with both of their linear and nonlinear components playing a role. For the linear component, its change appears to be more significant over the EEP (WEP) in the positive (negative) forcing scenario, favoring the seesaw pattern of the SST asymmetry. For the nonlinear component, its change acts to warm (cool) the EEP (WEP) in both scenarios, also favorable for the development of the SST asymmetry. Additional experiments with a slab ocean confirm the dominant role of ocean dynamical processes for this SST asymmetry. The net surface heat flux, in contrast, works to reduce the SST asymmetry through its shortwave radiation and latent heat flux components, with the former being related to the nonlinear relationship between SST and convection, and the latter being attributable to Newtonian damping and air-sea stability effects. The suppressing effect of shortwave radiation on SST asymmetry is further verified by partially coupled overriding experiments.« less

Asymmetric response of the equatorial Pacific SST to climate warming and cooling

NASA Astrophysics Data System (ADS)

Luo, Y.; Liu, F.; Lu, J.

2017-12-01

The response of the equatorial Pacific Ocean to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model (CESM). Results show a strong asymmetry in SST changes. In the eastern equatorial Pacific (EEP), the warming responding to the positive forcing exceeds the cooling to the negative forcing; while in the western equatorial Pacific (WEP), it is the other way around and the cooling surpasses the warming. This leads to a zonal dipole asymmetric structure, with positive values in the east and negative values in the west. A surface heat budget analysis suggests that the SST asymmetry is mainly resulted from the oceanic horizontal advection and vertical entrainment, with both of their linear and nonlinear components playing a role. For the linear component, its change appears to be more significant over the EEP (WEP) in the positive (negative) forcing scenario, favoring the seesaw pattern of the SST asymmetry. For the nonlinear component, its change acts to warm (cool) the EEP (WEP) in both scenarios, also favorable for the development of the SST asymmetry. Additional experiments with a slab ocean confirm the dominant role of ocean dynamical processes for this SST asymmetry. The net surface heat flux, in contrast, works to reduce the SST asymmetry through its shortwave radiation and latent heat flux components, with the former being related to the nonlinear relationship between SST and convection, and the latter being attributable to Newtonian damping and air-sea stability effects. The suppressing effect of shortwave radiation on SST asymmetry is further verified by partially coupled overriding experiments.

Comparison of forced-air warming systems with upper body blankets using a copper manikin of the human body.

PubMed

Bräuer, A; English, M J M; Steinmetz, N; Lorenz, N; Perl, T; Braun, U; Weyland, W

2002-09-01

Forced-air warming with upper body blankets has gained high acceptance as a measure for the prevention of intraoperative hypothermia. However, data on heat transfer with upper body blankets are not yet available. This study was conducted to determine the heat transfer efficacy of eight complete upper body warming systems and to gain more insight into the principles of forced-air warming. Heat transfer of forced-air warmers can be described as follows: Qdot;=h. DeltaT. A, where Qdot;= heat flux [W], h=heat exchange coefficient [W m-2 degrees C-1], DeltaT=temperature gradient between the blanket and surface [ degrees C], and A=covered area [m2]. We tested eight different forced-air warming systems: (1) Bair Hugger and upper body blanket (Augustine Medical Inc. Eden Prairie, MN); (2) Thermacare and upper body blanket (Gaymar Industries, Orchard Park, NY); (3) Thermacare (Gaymar Industries) with reusable Optisan upper body blanket (Willy Rüsch AG, Kernen, Germany); (4) WarmAir and upper body blanket (Cincinnati Sub-Zero Products, Cincinnati, OH); (5) Warm-Gard and single use upper body blanket (Luis Gibeck AB, Upplands Väsby, Sweden); (6) Warm-Gard and reusable upper body blanket (Luis Gibeck AB); (7) WarmTouch and CareDrape upper body blanket (Mallinckrodt Medical Inc., St. Luis, MO); and (8) WarmTouch and reusable MultiCover trade mark upper body blanket (Mallinckrodt Medical Inc.) on a previously validated copper manikin of the human body. Heat flux and surface temperature were measured with 11 calibrated heat flux transducers. Blanket temperature was measured using 11 thermocouples. The temperature gradient between the blanket and surface (DeltaT) was varied between -8 and +8 degrees C, and h was determined by linear regression analysis as the slope of DeltaT vs. heat flux. Mean DeltaT was determined for surface temperatures between 36 and 38 degrees C, as similar mean skin surface temperatures have been found in volunteers. The covered area was estimated to be 0.35 m2. Total heat flow from the blanket to the manikin was different for surface temperatures between 36 and 38 degrees C. At a surface temperature of 36 degrees C the heat flows were higher (4-26.6 W) than at surface temperatures of 38 degrees C (2.6-18.1 W). The highest total heat flow was delivered by the WarmTouch trade mark system with the CareDrape trade mark upper body blanket (18.1-26.6 W). The lowest total heat flow was delivered by the Warm-Gard system with the single use upper body blanket (2.6-4 W). The heat exchange coefficient varied between 15.1 and 36.2 W m-2 degrees C-1, and mean DeltaT varied between 0.5 and 3.3 degrees C. We found total heat flows of 2.6-26.6 W by forced-air warming systems with upper body blankets. However, the changes in heat balance by forced-air warming systems with upper body blankets are larger, as these systems are not only transferring heat to the body but are also reducing heat losses from the covered area to zero. Converting heat losses of approximately 37.8 W to heat gain, results in a 40.4-64.4 W change in heat balance. The differences between the systems result from different heat exchange coefficients and different mean temperature gradients. However, the combination of a high heat exchange coefficient with a high mean temperature gradient is rare. This fact offers some possibility to improve these systems.

Crystallographic texture of straight-rolled ?-uranium foils via neutron and X-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Einhorn, J. R.; Steiner, M. A.; Vogel, S. C.

The texture of recrystallized straight-rolled ?-uranium foils, a component in prospective irradiation target designs for medical isotope production, has been measured by neutron diffraction, as well as X-ray diffraction using both Cu and Mo sources. Variations in the penetration depth of neutron and X-ray radiation allow for determination of both the bulk and surface textures. The bulk ?-uranium foil texture is similar to the warm straight-rolled plate texture, with the addition of a notable splitting of the (001) poles along the transverse direction. The surface texture of the foils is similar to the bulk, with an additional (001) texture componentmore » that is oriented between the rolling and normal directions. Differences between the surface and bulk textures are expected to arise from shear forces during the rolling process and the influence that distinct strain histories have on subsequent texture evolution during recrystallization.« less

Crystallographic texture of straight-rolled ?-uranium foils via neutron and X-ray diffraction

DOE PAGES

Einhorn, J. R.; Steiner, M. A.; Vogel, S. C.; ...

2017-05-25

The texture of recrystallized straight-rolled ?-uranium foils, a component in prospective irradiation target designs for medical isotope production, has been measured by neutron diffraction, as well as X-ray diffraction using both Cu and Mo sources. Variations in the penetration depth of neutron and X-ray radiation allow for determination of both the bulk and surface textures. The bulk ?-uranium foil texture is similar to the warm straight-rolled plate texture, with the addition of a notable splitting of the (001) poles along the transverse direction. The surface texture of the foils is similar to the bulk, with an additional (001) texture componentmore » that is oriented between the rolling and normal directions. Differences between the surface and bulk textures are expected to arise from shear forces during the rolling process and the influence that distinct strain histories have on subsequent texture evolution during recrystallization.« less

Observational Evidence for Enhanced Greenhouse Effect Reinforcing Wintertime Arctic Amplification and Sea Ice Melting Onset

NASA Astrophysics Data System (ADS)

Cao, Y.; Liang, S.

2017-12-01

Despite an apparent hiatus in global warming, the Arctic climate continues to experience unprecedented changes. Summer sea ice is retreating at an accelerated rate, and surface temperatures in this region are rising at a rate double that of the global average, a phenomenon known as Arctic amplification. Although a lot of efforts have been made, the causes this unprecedented phenomenon remain unclear and are subjects of considerable debate. In this study, we report strong observational evidence, for the first time from long-term (1984-2014) spatially complete satellite records, that increased cloudiness and atmospheric water vapor in winter and spring have caused an extraordinary downward longwave radiative flux to the ice surface, which may then amplify the Arctic wintertime ice-surface warming. In addition, we also provide observed evidence that it is quite likely the enhancement of the wintertime greenhouse effect caused by water vapor and cloudiness has advanced the time of onset of ice melting in mid-May through inhibiting sea-ice refreezing in the winter and accelerating the pre-melting process in the spring, and in turn triggered the positive sea-ice albedo feedback process and accelerated the sea ice melting in the summer.

Changes in extremely hot days under stabilized 1.5 and 2.0 °C global warming scenarios as simulated by the HAPPI multi-model ensemble

NASA Astrophysics Data System (ADS)

Wehner, Michael; Stone, Dáithí; Mitchell, Dann; Shiogama, Hideo; Fischer, Erich; Graff, Lise S.; Kharin, Viatcheslav V.; Lierhammer, Ludwig; Sanderson, Benjamin; Krishnan, Harinarayan

2018-03-01

The half a degree additional warming, prognosis and projected impacts (HAPPI) experimental protocol provides a multi-model database to compare the effects of stabilizing anthropogenic global warming of 1.5 °C over preindustrial levels to 2.0 °C over these levels. The HAPPI experiment is based upon large ensembles of global atmospheric models forced by sea surface temperature and sea ice concentrations plausible for these stabilization levels. This paper examines changes in extremes of high temperatures averaged over three consecutive days. Changes in this measure of extreme temperature are also compared to changes in hot season temperatures. We find that over land this measure of extreme high temperature increases from about 0.5 to 1.5 °C over present-day values in the 1.5 °C stabilization scenario, depending on location and model. We further find an additional 0.25 to 1.0 °C increase in extreme high temperatures over land in the 2.0 °C stabilization scenario. Results from the HAPPI models are consistent with similar results from the one available fully coupled climate model. However, a complicating factor in interpreting extreme temperature changes across the HAPPI models is their diversity of aerosol forcing changes.

Discharge, water temperature, and water quality of Warm Mineral Springs, Sarasota County, Florida: A retrospective analysis

USGS Publications Warehouse

Metz, Patricia A.

2016-09-27

Warm Mineral Springs, located in southern Sarasota County, Florida, is a warm, highly mineralized, inland spring. Since 1946, a bathing spa has been in operation at the spring, attracting vacationers and health enthusiasts. During the winter months, the warm water attracts manatees to the adjoining spring run and provides vital habitat for these mammals. Well-preserved late Pleistocene to early Holocene-age human and animal bones, artifacts, and plant remains have been found in and around the spring, and indicate the surrounding sinkhole formed more than 12,000 years ago. The spring is a multiuse resource of hydrologic importance, ecological and archeological significance, and economic value to the community.The pool of Warm Mineral Springs has a circular shape that reflects its origin as a sinkhole. The pool measures about 240 feet in diameter at the surface and has a maximum depth of about 205 feet. The sinkhole developed in the sand, clay, and dolostone of the Arcadia Formation of the Miocene-age to Oligocene-age Hawthorn Group. Underlying the Hawthorn Group are Oligocene-age to Eocene-age limestones and dolostones, including the Suwannee Limestone, Ocala Limestone, and Avon Park Formation. Mineralized groundwater, under artesian pressure in the underlying aquifers, fills the remnant sink, and the overflow discharges into Warm Mineral Springs Creek, to Salt Creek, and subsequently into the Myakka River. Aquifers described in the vicinity of Warm Mineral Springs include the surficial aquifer system, the intermediate aquifer system within the Hawthorn Group, and the Upper Floridan aquifer in the Suwannee Limestone, Ocala Limestone, and Avon Park Formation. The Hawthorn Group acts as an upper confining unit of the Upper Floridan aquifer.Groundwater flow paths are inferred from the configuration of the potentiometric surface of the Upper Floridan aquifer for September 2010. Groundwater flow models indicate the downward flow of water into the Upper Floridan aquifer in inland areas, and upward flow toward the surface in coastal areas, such as at Warm Mineral Springs. Warm Mineral Springs is located in a discharge area. Changes in water use in the region have affected the potentiometric surface of the Upper Floridan aquifer. Historical increase in groundwater withdrawals resulted in a 10- to 20-foot regional decline in the potentiometric surface of the Upper Floridan aquifer by May 1975 relative to predevelopment levels and remained at approximately that level in May 2007 in the area of Warm Mineral Springs. Discharge measurements at Warm Mineral Springs (1942–2014) decreased from about 11–12 cubic feet per second in the 1940s to about 6–9 cubic feet per second in the 1970s and remained at about that level for the remainder of the period of record. Similarity of changes in regional water use and discharge at Warm Mineral Springs indicates that basin-scale changes to the groundwater system have affected discharge at Warm Mineral Springs. Water temperature had no significant trend in temperature over the period of record, 1943–2015, and outliers were identified in the data that might indicate inconsistencies in measurement methods or locations.Within the regional groundwater basin, Warm Mineral Springs is influenced by deep Upper Floridan aquifer flow paths that discharge toward the coast. Associated with these flow paths, the groundwater temperatures increase with depth and toward the coast. Multiple lines of evidence indicate that a source of warm groundwater to Warm Mineral Springs is likely the permeable zone of the Avon Park Formation within the Upper Floridan aquifer at a depth of about 1,400 to 1,600 feet, or deeper sources. The permeable zone contains saline groundwater with water temperatures of at least 95 degrees Fahrenheit.The water quality of Warm Mineral Springs, when compared with other springs in Florida had the highest temperature and the greatest mineralized content. Warm Mineral Springs water is characterized by a slight-green color, with varying water clarity, low dissolved oxygen (indicative of deep groundwater), and a hydrogen sulfide odor. Water-quality samples detected ammonium-nitrogen and nitrates, but at low concentrations. The drinking water standard for nitrate adopted by the U.S. Environmental Protection Agency is 10 milligrams per liter, measured as nitrogen. Water samples collected at spring vents by divers on April 29, 2015, had concentrations of 0.9 milligram per liter nitrate-nitrogen at vent A and 0.04–0.05 milligram per liter at vents B, C, and D. Typically, the water clarity is highest in the morning (about 30 feet Secchi depth) and often decreases throughout the day.Analysis of existing data provided some insight into the hydrologic processes affecting Warm Mineral Springs; however, data have been sparsely and discontinuously collected since the 1940s. Continuous monitoring of hydrologic characteristics such as discharge, water temperature, specific conductance, and water-quality indicators, such as nitrate and turbidity (water clarity), would be valuable for monitoring and development of models of spring discharge and water quality. In addition, water samples could be analyzed for isotopic tracers, such as strontium, and the results used to identify and quantify the sources of groundwater that discharge at Warm Mineral Springs. Groundwater flow/transport models could be used to evaluate the sensitivity of the quality and quantity of water flowing from Warm Mineral Springs to changes in climate, aquifer levels, and water use.

Super Clausius-Clapeyron scaling of extreme hourly precipitation and its relation to large-scale atmospheric conditions

NASA Astrophysics Data System (ADS)

Lenderink, Geert; Barbero, Renaud; Loriaux, Jessica; Fowler, Hayley

2017-04-01

Present-day precipitation-temperature scaling relations indicate that hourly precipitation extremes may have a response to warming exceeding the Clausius-Clapeyron (CC) relation; for The Netherlands the dependency on surface dew point temperature follows two times the CC relation corresponding to 14 % per degree. Our hypothesis - as supported by a simple physical argument presented here - is that this 2CC behaviour arises from the physics of convective clouds. So, we think that this response is due to local feedbacks related to the convective activity, while other large scale atmospheric forcing conditions remain similar except for the higher temperature (approximately uniform warming with height) and absolute humidity (corresponding to the assumption of unchanged relative humidity). To test this hypothesis, we analysed the large-scale atmospheric conditions accompanying summertime afternoon precipitation events using surface observations combined with a regional re-analysis for the data in The Netherlands. Events are precipitation measurements clustered in time and space derived from approximately 30 automatic weather stations. The hourly peak intensities of these events again reveal a 2CC scaling with the surface dew point temperature. The temperature excess of moist updrafts initialized at the surface and the maximum cloud depth are clear functions of surface dew point temperature, confirming the key role of surface humidity on convective activity. Almost no differences in relative humidity and the dry temperature lapse rate were found across the dew point temperature range, supporting our theory that 2CC scaling is mainly due to the response of convection to increases in near surface humidity, while other atmospheric conditions remain similar. Additionally, hourly precipitation extremes are on average accompanied by substantial large-scale upward motions and therefore large-scale moisture convergence, which appears to accelerate with surface dew point. This increase in large-scale moisture convergence appears to be consequence of latent heat release due to the convective activity as estimated from the quasi-geostrophic omega equation. Consequently, most hourly extremes occur in precipitation events with considerable spatial extent. Importantly, this event size appears to increase rapidly at the highest dew point temperature range, suggesting potentially strong impacts of climatic warming.

Observation of local cloud and moisture feedbacks over high ocean and desert surface temperatures

NASA Technical Reports Server (NTRS)

Chahine, Moustafa T.

1995-01-01

New data on clouds and moisture, made possible by reanalysis of weather satellite observations, show that the atmosphere reacts to warm clusters of very high sea surface temperatures in the western Pacific Ocean with increased moisture, cloudiness, and convection, suggesting a negative feedback limiting the sea surface temperature rise. The reverse was observed over dry and hot deserts where both moisture and cloudiness decrease, suggesting a positive feedback perpetuating existing desert conditions. In addition, the observations show a common critical surface temperature for both oceans and land; the distribution of atmospheric moisture is observed to reach a maximum value when the daily surface temperatures approach 304 +/- 1 K. These observations reveal complex dynamic-radiative interactions where multiple processes act simultaneously at the surface as well as in the atmosphere to regulate the feedback processes.

Water-Surface Elevations, Discharge, and Water-Quality Data for Selected Sites in the Warm Springs Area near Moapa, Nevada

USGS Publications Warehouse

Beck, David A.; Ryan, Roslyn; Veley, Ronald J.; Harper, Donald P.; Tanko, Daron J.

2006-01-01

The U.S. Geological Survey, in cooperation with Southern Nevada Water Authority and the Nevada Division of Water Resources, operates and maintains a surface-water monitoring network of 6 continuous-record stream-flow gaging stations and 11 partial-record stations in the Warm Springs area near Moapa, Nevada. Permanent land-surface bench marks were installed within the Warm Springs area by the Las Vegas Valley Water District, the Southern Nevada Water Authority, and the U.S. Geological Survey to determine water-surface elevations at all network monitoring sites. Vertical datum elevation and horizontal coordinates were established for all bench marks through a series of Differential Global Positioning System surveys. Optical theodolite surveys were made to transfer Differential Global Positioning System vertical datums to reference marks installed at each monitoring site. The surveys were completed in June 2004 and water-surface elevations were measured on August 17, 2004. Water-surface elevations ranged from 1,810.33 feet above North American Vertical Datum of 1988 at a stream-gaging station in the Pederson Springs area to 1,706.31 feet at a station on the Muddy River near Moapa. Discharge and water-quality data were compiled for the Warm Springs area and include data provided by the U.S. Geological Survey, Nevada Division of Water Resources, U.S. Fish and Wildlife Service, Moapa Valley Water District, Desert Research Institute, and Converse Consultants. Historical and current hydrologic data-collection networks primarily are related to changes in land- and water-use activities in the Warm Springs area. These changes include declines in ranching and agricultural use, the exportation of water to other areas of Moapa Valley, and the creation of a national wildlife refuge. Water-surface elevations, discharge, and water-quality data compiled for the Warm Springs area will help identify (1) effects of changing vegetation within the former agricultural lands, (2) effects of restoration activities in the wildlife refuge, and (3) potential impacts of ground-water withdrawals.

Warming of the Global Ocean: Spatial Structure and Water-Mass Trends

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Rhines, Peter B.; Worthen, Denise L.

2016-01-01

This study investigates the multidecadal warming and interannual-to-decadal heat content changes in the upper ocean (0-700 m), focusing on vertical and horizontal patterns of variability. These results support a nearly monotonic warming over much of the World Ocean, with a shift toward Southern Hemisphere warming during the well-observed past decade. This is based on objectively analyzed gridded observational datasets and on a modeled state estimate. Besides the surface warming, a warming climate also has a subsurface effect manifesting as a strong deepening of the midthermocline isopycnals, which can be diagnosed directly from hydrographic data. This deepening appears to be a result of heat entering via subduction and spreading laterally from the high-latitude ventilation regions of subtropical mode waters. The basin-average multidecadal warming mainly expands the subtropical mode water volume, with weak changes in the temperature-salinity (u-S) relationship (known as ''spice'' variability). However, the spice contribution to the heat content can be locally large, for example in Southern Hemisphere. Multidecadal isopycnal sinking has been strongest over the southern basins and weaker elsewhere with the exception of the Gulf Stream/North Atlantic Current/subtropical recirculation gyre. At interannual to decadal time scales, wind-driven sinking and shoaling of density surfaces still dominate ocean heat content changes, while the contribution from temperature changes along density surfaces tends to decrease as time scales shorten.

Trends in continental temperature and humidity directly linked to ocean warming.

PubMed

Byrne, Michael P; O'Gorman, Paul A

2018-05-08

In recent decades, the land surface has warmed substantially more than the ocean surface, and relative humidity has fallen over land. Amplified warming and declining relative humidity over land are also dominant features of future climate projections, with implications for climate-change impacts. An emerging body of research has shown how constraints from atmospheric dynamics and moisture budgets are important for projected future land-ocean contrasts, but these ideas have not been used to investigate temperature and humidity records over recent decades. Here we show how both the temperature and humidity changes observed over land between 1979 and 2016 are linked to warming over neighboring oceans. A simple analytical theory, based on atmospheric dynamics and moisture transport, predicts equal changes in moist static energy over land and ocean and equal fractional changes in specific humidity over land and ocean. The theory is shown to be consistent with the observed trends in land temperature and humidity given the warming over ocean. Amplified land warming is needed for the increase in moist static energy over drier land to match that over ocean, and land relative humidity decreases because land specific humidity is linked via moisture transport to the weaker warming over ocean. However, there is considerable variability about the best-fit trend in land relative humidity that requires further investigation and which may be related to factors such as changes in atmospheric circulations and land-surface properties.

Increased future ice discharge from Antarctica owing to higher snowfall.

PubMed

Winkelmann, R; Levermann, A; Martin, M A; Frieler, K

2012-12-13

Anthropogenic climate change is likely to cause continuing global sea level rise, but some processes within the Earth system may mitigate the magnitude of the projected effect. Regional and global climate models simulate enhanced snowfall over Antarctica, which would provide a direct offset of the future contribution to global sea level rise from cryospheric mass loss and ocean expansion. Uncertainties exist in modelled snowfall, but even larger uncertainties exist in the potential changes of dynamic ice discharge from Antarctica and thus in the ultimate fate of the precipitation-deposited ice mass. Here we show that snowfall and discharge are not independent, but that future ice discharge will increase by up to three times as a result of additional snowfall under global warming. Our results, based on an ice-sheet model forced by climate simulations through to the end of 2500 (ref. 8), show that the enhanced discharge effect exceeds the effect of surface warming as well as that of basal ice-shelf melting, and is due to the difference in surface elevation change caused by snowfall on grounded versus floating ice. Although different underlying forcings drive ice loss from basal melting versus increased snowfall, similar ice dynamical processes are nonetheless at work in both; therefore results are relatively independent of the specific representation of the transition zone. In an ensemble of simulations designed to capture ice-physics uncertainty, the additional dynamic ice loss along the coastline compensates between 30 and 65 per cent of the ice gain due to enhanced snowfall over the entire continent. This results in a dynamic ice loss of up to 1.25 metres in the year 2500 for the strongest warming scenario. The reported effect thus strongly counters a potential negative contribution to global sea level by the Antarctic Ice Sheet.

Warm Rivers Play Role in Arctic Sea Ice Melt Animation

NASA Image and Video Library

2014-03-05

This frame from a NASA MODIS animation depicts warming sea surface temperatures in the Arctic Beaufort Sea after warm waters from Canada Mackenzie River broke through a shoreline sea ice barrier in summer 2012, enhancing the melting of sea ice.

CLIMATE CHANGE. Possible artifacts of data biases in the recent global surface warming hiatus.

PubMed

Karl, Thomas R; Arguez, Anthony; Huang, Boyin; Lawrimore, Jay H; McMahon, James R; Menne, Matthew J; Peterson, Thomas C; Vose, Russell S; Zhang, Huai-Min

2015-06-26

Much study has been devoted to the possible causes of an apparent decrease in the upward trend of global surface temperatures since 1998, a phenomenon that has been dubbed the global warming "hiatus." Here, we present an updated global surface temperature analysis that reveals that global trends are higher than those reported by the Intergovernmental Panel on Climate Change, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a "slowdown" in the increase of global surface temperature. Copyright © 2015, American Association for the Advancement of Science.

Detecting the global and regional effects of sulphate aerosol geoengineering

NASA Astrophysics Data System (ADS)

Lo, Eunice; Charlton-Perez, Andrew; Highwood, Ellie

2017-04-01

Climate warming is unequivocal. In addition to carbon dioxide emission mitigation, some geoengineering ideas have been proposed to reduce future surface temperature rise. One of these proposals involves injecting sulphate aerosols into the stratosphere to increase the planet's albedo. Monitoring the effectiveness of sulphate aerosol injection (SAI) would require us to be able to distinguish and detect its cooling effect from the climate system's internal variability and other externally forced temperature changes. This research uses optimal fingerprinting techniques together with simulations from the GeoMIP data base to estimate the number of years of observations that would be needed to detect SAI's cooling signal in near-surface air temperature, should 5 Tg of sulphur dioxide be injected into the stratosphere per year on top of RCP4.5 from 2020-2070. The first part of the research compares the application of two detection methods that have different null hypotheses to SAI detection in global mean near-surface temperature. The first method assumes climate noise to be dominated by unforced climate variability and attempts to detect the SAI cooling signal and greenhouse gas driven warming signal in the "observations" simultaneously against this noise. The second method considers greenhouse gas driven warming to be a non-stationary background climate and attempts to detect the net cooling effect of SAI against this background. Results from this part of the research show that the conventional multi-variate detection method that has been extensively used to attribute climate warming to anthropogenic sources could also be applied for geoengineering detection. The second part of the research investigates detection of geoengineering effects on the regional scale. The globe is divided into various sub-continental scale regions and the cooling effect of SAI is looked for in the temperature time series in each of these regions using total least squares multi-variate detection. Results show that surface temperature observations would be most useful for SAI detection in the Northern Hemisphere mid-latitudes, especially in East Asia. This can be used to indicate the optimal observational network for monitoring the effectiveness of SAI in the future, should that be needed.

The footprint of the inter-decadal Pacific oscillation in Indian Ocean sea surface temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Lu; Zhou, Tianjun; Dai, Aiguo

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871–2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcingsmore » account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. As a result, the decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.« less

The footprint of the inter-decadal Pacific oscillation in Indian Ocean sea surface temperatures

DOE PAGES

Dong, Lu; Zhou, Tianjun; Dai, Aiguo; ...

2016-02-17

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871–2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcingsmore » account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. As a result, the decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.« less

Sea surface height evidence for long-term warming effects of tropical cyclones on the ocean

PubMed Central

Mei, Wei; Primeau, François; McWilliams, James C.; Pasquero, Claudia

2013-01-01

Tropical cyclones have been hypothesized to influence climate by pumping heat into the ocean, but a direct measure of this warming effect is still lacking. We quantified cyclone-induced ocean warming by directly monitoring the thermal expansion of water in the wake of cyclones, using satellite-based sea surface height data that provide a unique way of tracking the changes in ocean heat content on seasonal and longer timescales. We find that the long-term effect of cyclones is to warm the ocean at a rate of 0.32 ± 0.15 PW between 1993 and 2009, i.e., ∼23 times more efficiently per unit area than the background equatorial warming, making cyclones potentially important modulators of the climate by affecting heat transport in the ocean–atmosphere system. Furthermore, our analysis reveals that the rate of warming increases with cyclone intensity. This, together with a predicted shift in the distribution of cyclones toward higher intensities as climate warms, suggests the ocean will get even warmer, possibly leading to a positive feedback. PMID:23922393

Sea surface height evidence for long-term warming effects of tropical cyclones on the ocean.

PubMed

Mei, Wei; Primeau, François; McWilliams, James C; Pasquero, Claudia

2013-09-17

Tropical cyclones have been hypothesized to influence climate by pumping heat into the ocean, but a direct measure of this warming effect is still lacking. We quantified cyclone-induced ocean warming by directly monitoring the thermal expansion of water in the wake of cyclones, using satellite-based sea surface height data that provide a unique way of tracking the changes in ocean heat content on seasonal and longer timescales. We find that the long-term effect of cyclones is to warm the ocean at a rate of 0.32 ± 0.15 PW between 1993 and 2009, i.e., ∼23 times more efficiently per unit area than the background equatorial warming, making cyclones potentially important modulators of the climate by affecting heat transport in the ocean-atmosphere system. Furthermore, our analysis reveals that the rate of warming increases with cyclone intensity. This, together with a predicted shift in the distribution of cyclones toward higher intensities as climate warms, suggests the ocean will get even warmer, possibly leading to a positive feedback.

The 2014/15 Warm Anomaly in the Southern California Current - Physical and Biological Responses

NASA Astrophysics Data System (ADS)

Ralf, G.

2016-02-01

The 2014/15 Warm Anomaly (WarmA) off Southern California manifested itself in the summer of 2014 as an anomalously warm surface layer in the Southern Calif. Bight with low concentrations of Chl a. This layer intensified in spatial extent, covering the entire CalCOFI surface area by the winter of 2015 with temperature anomalies 3 StDev larger than long-term averages. Concentrations of nutrients, phytoplankton biomass and rates of primary production were extremely low during the WarmA. The evolution of the WarmA as well as the 2015/16 El Niño with time will be compared to the evolution of the weak and strong El Niño's observed over the last 60 years. These events provide unique insights in the controls of phytoplankton biomass and production in the southern California Current System. Preliminary analyses suggest that the response of the phytoplankton community to the WarmA was consistent with responses to similar forcing during the prior decade. This presentation is based on data collected during the quarterly CalCOFI cruises by the CalCOFI and the CCE-LTER groups.

Lower-limb warming improves sleep quality in elderly people living in nursing homes.

PubMed

Oshima-Saeki, Chika; Taniho, Yuiko; Arita, Hiromi; Fujimoto, Etsuko

2017-01-01

Sleep disturbances are common in older people. This study was conducted to examine the effects of a hot pack, which was used to warm the lower limbs, on the sleep of elderly people living in a nursing home. This is a prospective cohort involving seven elderly women. Subjects aged 74-93 years old were treated by warming the lower limbs for 40 minutes using hot packs every night over 8 weeks. A hot pack made of a dense polymer and warmed in a microwave oven was used as a warming device. In the first and last week, the subjects were required to wear an activity monitor to determine their sleep-awake status. During the second to ninth week, they received limb-warming treatment by a hot pack heated to 42ºC for 40 min every night. Surface skin temperature data were collected by thermographic measurement. As a result, lower-limb warming by a hot pack significantly improved the quality of sleep in the subjects. During warming, the surface temperature of the hands and face rose by approximately 0.5-1.5ºC. This study showed that lower-limb warming with a hot pack reduced sleep latency and wake episodes after sleep onset; thus, improving the quality of sleep in elderly people living in a nursing home.

North Atlantic Surface Winds Examined as the Source of Warm Advection into Europe in Winter

NASA Technical Reports Server (NTRS)

Otterman, J.; Angell, J. K.; Ardizzone, J.; Atlas, Robert; Schubert, S.; Starr, D.; Wu, M.-L.

2002-01-01

When from the southwest, North Atlantic ocean surface winds are known to bring warm and moist airmasses into central Europe in winter. By tracing backward trajectories from western Europe, we establish that these airmasses originate in the southwestern North Atlantic, in the very warm regions of the Gulf Stream. Over the eastern North Atlantic, Lt the gateway to Europe, the ocean-surface winds changed directions in the second half of the XXth century, those from the northwest and from the southeast becoming so infrequent, that the direction from the southwest became even more dominant. For the January-to-March period, the strength of south-westerlies in this region, as well as in the source region, shows in the years 1948-1995 a significant increase, above 0.2 m/sec/ decade. Based on the sensitivity of the surface temperature in Europe, slightly more than 1 C for a 1m/sec increase in the southwesterly wind, found in the previous studies, the trend in the warm advection accounts for a large part of the warming in Europe established for this period in several reports. However, for the most recent years, 1996-2001, the positive trend in the southwesterly advection appears to be is broken, which is consistent with unseasonally cold events reported in Europe in those winters. This study had, some bearing on evaluating the respective roles of the North Atlantic Oscillation and the Greenhouse Gas Global warming, GGG, in the strong winter warming observed for about half a century over the northern-latitude continents. Changes in the ocean-surface temperatures induced by GGG may have produced the dominant southwesterly direction of the North Atlantic winds. However, this implies a monotonically (apart from inherent interannual variability) increasing advection, and if the break in the trend which we observe after 1995 persists, this mechanism is counter-indicated. The 1948-1995 trend in the south-westerlies could then be considered to a large degree attributable to the North Atlantic Oscillation.

Adjusting Mitigation Pathways to Stabilize Climate at 1.5°C and 2.0°C Rise in Global Temperatures to Year 2300

NASA Astrophysics Data System (ADS)

Goodwin, Philip; Brown, Sally; Haigh, Ivan David; Nicholls, Robert James; Matter, Juerg M.

2018-03-01

To avoid the most dangerous consequences of anthropogenic climate change, the Paris Agreement provides a clear and agreed climate mitigation target of stabilizing global surface warming to under 2.0°C above preindustrial, and preferably closer to 1.5°C. However, policy makers do not currently know exactly what carbon emissions pathways to follow to stabilize warming below these agreed targets, because there is large uncertainty in future temperature rise for any given pathway. This large uncertainty makes it difficult for a cautious policy maker to avoid either: (1) allowing warming to exceed the agreed target or (2) cutting global emissions more than is required to satisfy the agreed target, and their associated societal costs. This study presents a novel Adjusting Mitigation Pathway (AMP) approach to restrict future warming to policy-driven targets, in which future emissions reductions are not fully determined now but respond to future surface warming each decade in a self-adjusting manner. A large ensemble of Earth system model simulations, constrained by geological and historical observations of past climate change, demonstrates our self-adjusting mitigation approach for a range of climate stabilization targets ranging from 1.5°C to 4.5°C, and generates AMP scenarios up to year 2300 for surface warming, carbon emissions, atmospheric CO2, global mean sea level, and surface ocean acidification. We find that lower 21st century warming targets will significantly reduce ocean acidification this century, and will avoid up to 4 m of sea-level rise by year 2300 relative to a high-end scenario.

Spatiotemporal variability in surface energy balance across tundra, snow and ice in Greenland.

PubMed

Lund, Magnus; Stiegler, Christian; Abermann, Jakob; Citterio, Michele; Hansen, Birger U; van As, Dirk

2017-02-01

The surface energy balance (SEB) is essential for understanding the coupled cryosphere-atmosphere system in the Arctic. In this study, we investigate the spatiotemporal variability in SEB across tundra, snow and ice. During the snow-free period, the main energy sink for ice sites is surface melt. For tundra, energy is used for sensible and latent heat flux and soil heat flux leading to permafrost thaw. Longer snow-free period increases melting of the Greenland Ice Sheet and glaciers and may promote tundra permafrost thaw. During winter, clouds have a warming effect across surface types whereas during summer clouds have a cooling effect over tundra and a warming effect over ice, reflecting the spatial variation in albedo. The complex interactions between factors affecting SEB across surface types remain a challenge for understanding current and future conditions. Extended monitoring activities coupled with modelling efforts are essential for assessing the impact of warming in the Arctic.

Understanding the tropical warm temperature bias simulated by climate models

NASA Astrophysics Data System (ADS)

Brient, Florent; Schneider, Tapio

2017-04-01

The state-of-the-art coupled general circulation models have difficulties in representing the observed spatial pattern of surface tempertaure. A majority of them suffers a warm bias in the tropical subsiding regions located over the eastern parts of oceans. These regions are usually covered by low-level clouds scattered from stratus along the coasts to more vertically developed shallow cumulus farther from them. Models usually fail to represent accurately this transition. Here we investigate physical drivers of this warm bias in CMIP5 models through a near-surface energy budget perspective. We show that overestimated solar insolation due to a lack of stratocumulus mostly explains the warm bias. This bias also arises partly from inter-model differences in surface fluxes that could be traced to differences in near-surface relative humidity and air-sea temperature gradient. We investigate the role of the atmosphere in driving surface biases by comparing historical and atmopsheric (AMIP) experiments. We show that some differences in boundary-layer characteristics, mostly those related to cloud fraction and relative humidity, are already present in AMIP experiments and may be the drivers of coupled biases. This gives insights in how models can be improved for better simulations of the tropical climate.

The Response of Phanerozoic Surface Temperature to Variations in Atmospheric Oxygen Concentration

NASA Astrophysics Data System (ADS)

Payne, R. C.; Britt, A. V.; Chen, H.; Kasting, J. F.; Catling, D. C.

2016-12-01

Recently, Poulsen et al. (2015) suggested that O2 has played a major role in climate forcing during the Phanerozoic. Specifically, they argued that decreased O2 levels during the Cenomanian stage of the mid-Cretaceous (94-100 Ma) could help explain the extremely warm climate during that time. The postulated warming mechanism involves decreased Rayleigh scattering by a thinner atmosphere, which reduces the planetary albedo and allows greater surface warming. This warming effect is then amplified by cloud feedbacks within their 3-D climate model. This increase in shortwave surface forcing, in their calculations, exceeds any decrease in the greenhouse effect caused by decreased O2, so that surface temperature increases by 2.1 K with low oxygen. Here, we use a 1-D radiative-convective climate model (with no cloud feedbacks) to check their results. We also include a self-consistent calculation of the change in atmospheric ozone and its effect on climate. Our results are opposite to those of Poulsen et al.: we find that the climate warms by 1.4 K at 35% O2 concentrations as a result of increased pressure broadening of CO2 and H2O absorption lines, and cools by 0.8 K at 10% O2 as a result of decreased pressure broadening. The surface temperature changes are only about 1 K either way, though, for reasonable variations in Phanerozoic O2 concentrations (10% - 35% by volume), and the Poulsen et al. (2016) results appear to be largely driven by cloud feedbacks in their model. Hence, it seems unlikely that changes in atmospheric O2 account for the warm climate of the Cenomanian. Other factors, such as a higher-than-expected sensitivity of climate to increased CO2 concentrations, may be required to obtain agreement with the paleoclimate data.

Regional Contrasts of the Warming Rate over Land Significantly Depend on the Calculation Methods of Mean Air Temperature

NASA Astrophysics Data System (ADS)

Wang, Kaicun; Zhou, Chunlüe

2016-04-01

Global analyses of surface mean air temperature (Tm) are key datasets for climate change studies and provide fundamental evidences for global warming. However, the causes of regional contrasts in the warming rate revealed by such datasets, i.e., enhanced warming rates over the northern high latitudes and the "warming hole" over the central U.S., are still under debate. Here we show these regional contrasts depends on the calculation methods of Tm. Existing global analyses calculated Tm from daily minimum and maximum temperatures (T2). We found that T2 has a significant standard deviation error of 0.23 °C/decade in depicting the regional warming rate from 2000 to 2013 but can be reduced by two-thirds using Tm calculated from observations at four specific times (T4), which samples diurnal cycle of land surface air temperature more often. From 1973 to 1997, compared with T4, T2 significantly underestimated the warming rate over the central U.S. and overestimated the warming rate over the northern high latitudes. The ratio of the warming rate over China to that over the U.S. reduces from 2.3 by T2 to 1.4 by T4. This study shows that the studies of regional warming can be substantially improved by T4 instead of T2.

Suppressed mid-latitude summer atmospheric warming by Arctic sea ice loss during 1979-2012

NASA Astrophysics Data System (ADS)

Wu, Q.

2016-12-01

Since the 1980s, rapid Arctic warming, sea ice decline, and weakening summer circulation have coincided with an increasing number of extreme heatwaves and other destructive weather events in the Northern Hemisphere (NH) mid-latitudes in summer. Recent papers disagree about whether such high-impact events are related to Arctic warming and/or ice loss. Here we use atmospheric model ensemble simulations to attribute effects of sea ice loss and other factors on observed summer climate trends during 1979-2012. The ongoing greenhouse gas buildup and resulting sea surface temperature (SST) warming outside the Arctic explains nearly all land warming and a significant portion of observed weakening zonal winds in the NH mid-latitudes. However, sea ice loss has induced a negative Arctic Oscillation (AO)-type circulation with significant summer surface and tropospheric cooling trends over large portions of the NH mid-latitudes, which reduce the warming and might reduce the probability of regional severe hot summers.

Competition between global warming and an abrupt collapse of the AMOC in Earth’s energy imbalance

PubMed Central

Drijfhout, Sybren

2015-01-01

A collapse of the Atlantic Meridional Overturning Circulation (AMOC) leads to global cooling through fast feedbacks that selectively amplify the response in the Northern Hemisphere (NH). How such cooling competes with global warming has long been a topic for speculation, but was never addressed using a climate model. Here it is shown that global cooling due to a collapsing AMOC obliterates global warming for a period of 15–20 years. Thereafter, the global mean temperature trend is reversed and becomes similar to a simulation without an AMOC collapse. The resulting surface warming hiatus lasts for 40–50 years. Global warming and AMOC-induced NH cooling are governed by similar feedbacks, giving rise to a global net radiative imbalance of similar sign, although the former is associated with surface warming, the latter with cooling. Their footprints in outgoing longwave and absorbed shortwave radiation are very distinct, making attribution possible. PMID:26437599

Potential vorticity regimes over East Asia during winter

NASA Astrophysics Data System (ADS)

Huang, Wenyu; Chen, Ruyan; Wang, Bin; Wright, Jonathon S.; Yang, Zifan; Ma, Wenqian

2017-02-01

Nine potential vorticity (PV) regimes over East Asia are identified by applying a Self-Organizing Map and Hierarchical Ascendant Classification regime analysis to the daily PV reanalysis fields on the 300 K isentropic surface for December-March 1948-2014. According to the surface temperature anomalies over East Asia, these nine regimes are further classified into three classes, i.e., cold class (three regimes), warm class (four regimes), and neutral class (two regimes). The PV-based East Asian winter monsoon index (EAWMI) is used to study the relationship between PV distributions and the temperature anomalies. The magnitude of cold (warm) anomalies over the land areas of East Asia increases (decreases) quasi-linearly with the EAWMI. Regression analysis reveals that cold temperature anomalies preferentially occur when the EAWMI exceeds a threshold at ˜0.2 PVU (where 1 PVU ≡ 10-6 m2 K kg-1 s-1). PV inversion uncovers the mechanisms behind the relationships between the PV regimes and surface temperature anomalies and reveals that cold (warm) PV regimes are associated with significant warming (cooling) in the upper troposphere and lower stratosphere. On average, cold regimes have longer durations than warm regimes. Interclass transition probabilities are much higher for paths from warm/neutral regimes to cold regimes than for paths from cold regimes to warm/neutral regimes. Besides, intraclass transitions are rare within the warm or neutral regimes. The PV regime analysis provides insight into the causes of severe cold spells over East Asia, with blocking circulation patterns identified as the primary factor in initiating and maintaining these cold spells.

Observed high-altitude warming and snow cover retreat over Tibet and the Himalayas enhanced by black carbon aerosols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Y.; Ramanathan, V.; Washington, W. M.

Himalayan mountain glaciers and the snowpack over the Tibetan Plateau provide the headwater of several major rivers in Asia. In situ observations of snow cover extent since the 1960s suggest that the snowpack in the region have retreated significantly, accompanied by a surface warming of 2–2.5°C observed over the peak altitudes (5000 m). Using a high-resolution ocean–atmosphere global climate model and an observationally constrained black carbon (BC) aerosol forcing, we attribute the observed altitude dependence of the warming trends as well as the spatial pattern of reductions in snow depths and snow cover extent to various anthropogenic factors. At themore » Tibetan Plateau altitudes, the increase in atmospheric CO 2 concentration exerted a warming of 1.7°C, BC 1.3°C where as cooling aerosols cause about 0.7°C cooling, bringing the net simulated warming consistent with the anomalously large observed warming. We therefore conclude that BC together with CO 2 has contributed to the snow retreat trends. In particular, BC increase is the major factor in the strong elevation dependence of the observed surface warming. The atmospheric warming by BC as well as its surface darkening of snow is coupled with the positive snow albedo feedbacks to account for the disproportionately large role of BC in high-elevation regions. Here, these findings reveal that BC impact needs to be properly accounted for in future regional climate projections, in particular on high-altitude cryosphere.« less

Observed high-altitude warming and snow cover retreat over Tibet and the Himalayas enhanced by black carbon aerosols

DOE PAGES

Xu, Y.; Ramanathan, V.; Washington, W. M.

2016-02-05

Himalayan mountain glaciers and the snowpack over the Tibetan Plateau provide the headwater of several major rivers in Asia. In situ observations of snow cover extent since the 1960s suggest that the snowpack in the region have retreated significantly, accompanied by a surface warming of 2–2.5°C observed over the peak altitudes (5000 m). Using a high-resolution ocean–atmosphere global climate model and an observationally constrained black carbon (BC) aerosol forcing, we attribute the observed altitude dependence of the warming trends as well as the spatial pattern of reductions in snow depths and snow cover extent to various anthropogenic factors. At themore » Tibetan Plateau altitudes, the increase in atmospheric CO 2 concentration exerted a warming of 1.7°C, BC 1.3°C where as cooling aerosols cause about 0.7°C cooling, bringing the net simulated warming consistent with the anomalously large observed warming. We therefore conclude that BC together with CO 2 has contributed to the snow retreat trends. In particular, BC increase is the major factor in the strong elevation dependence of the observed surface warming. The atmospheric warming by BC as well as its surface darkening of snow is coupled with the positive snow albedo feedbacks to account for the disproportionately large role of BC in high-elevation regions. Here, these findings reveal that BC impact needs to be properly accounted for in future regional climate projections, in particular on high-altitude cryosphere.« less

Combined effects of night warming and light pollution on predator-prey interactions.

PubMed

Miller, Colleen R; Barton, Brandon T; Zhu, Likai; Radeloff, Volker C; Oliver, Kerry M; Harmon, Jason P; Ives, Anthony R

2017-10-11

Interactions between multiple anthropogenic environmental changes can drive non-additive effects in ecological systems, and the non-additive effects can in turn be amplified or dampened by spatial covariation among environmental changes. We investigated the combined effects of night-time warming and light pollution on pea aphids and two predatory ladybeetle species. As expected, neither night-time warming nor light pollution changed the suppression of aphids by the ladybeetle species that forages effectively in darkness. However, for the more-visual predator, warming and light had non-additive effects in which together they caused much lower aphid abundances. These results are particularly relevant for agriculture near urban areas that experience both light pollution and warming from urban heat islands. Because warming and light pollution can have non-additive effects, predicting their possible combined consequences over broad spatial scales requires knowing how they co-occur. We found that night-time temperature change since 1949 covaried positively with light pollution, which has the potential to increase their non-additive effects on pea aphid control by 70% in US alfalfa. Our results highlight the importance of non-additive effects of multiple environmental factors on species and food webs, especially when these factors co-occur. © 2017 The Author(s).

Warming of subarctic tundra increases emissions of all three important greenhouse gases - carbon dioxide, methane, and nitrous oxide.

PubMed

Voigt, Carolina; Lamprecht, Richard E; Marushchak, Maija E; Lind, Saara E; Novakovskiy, Alexander; Aurela, Mika; Martikainen, Pertti J; Biasi, Christina

2017-08-01

Rapidly rising temperatures in the Arctic might cause a greater release of greenhouse gases (GHGs) to the atmosphere. To study the effect of warming on GHG dynamics, we deployed open-top chambers in a subarctic tundra site in Northeast European Russia. We determined carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) fluxes as well as the concentration of those gases, inorganic nitrogen (N) and dissolved organic carbon (DOC) along the soil profile. Studied tundra surfaces ranged from mineral to organic soils and from vegetated to unvegetated areas. As a result of air warming, the seasonal GHG budget of the vegetated tundra surfaces shifted from a GHG sink of -300 to -198 g CO 2 -eq m -2 to a source of 105 to 144 g CO 2 -eq m -2 . At bare peat surfaces, we observed increased release of all three GHGs. While the positive warming response was dominated by CO 2 , we provide here the first in situ evidence of increasing N 2 O emissions from tundra soils with warming. Warming promoted N 2 O release not only from bare peat, previously identified as a strong N 2 O source, but also from the abundant, vegetated peat surfaces that do not emit N 2 O under present climate. At these surfaces, elevated temperatures had an adverse effect on plant growth, resulting in lower plant N uptake and, consequently, better N availability for soil microbes. Although the warming was limited to the soil surface and did not alter thaw depth, it increased concentrations of DOC, CO 2, and CH 4 in the soil down to the permafrost table. This can be attributed to downward DOC leaching, fueling microbial activity at depth. Taken together, our results emphasize the tight linkages between plant and soil processes, and different soil layers, which need to be taken into account when predicting the climate change feedback of the Arctic. © 2016 John Wiley & Sons Ltd.

Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming.

PubMed

Cronin, Timothy W; Tziperman, Eli

2015-09-15

High-latitude continents have warmed much more rapidly in recent decades than the rest of the globe, especially in winter, and the maintenance of warm, frost-free conditions in continental interiors in winter has been a long-standing problem of past equable climates. We use an idealized single-column atmospheric model across a range of conditions to study the polar night process of air mass transformation from high-latitude maritime air, with a prescribed initial temperature profile, to much colder high-latitude continental air. We find that a low-cloud feedback--consisting of a robust increase in the duration of optically thick liquid clouds with warming of the initial state--slows radiative cooling of the surface and amplifies continental warming. This low-cloud feedback increases the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature, effectively suppressing Arctic air formation. The time it takes for the surface air temperature to drop below freezing increases nonlinearly to ∼ 10 d for initial maritime surface air temperatures of 20 °C. These results, supplemented by an analysis of Coupled Model Intercomparison Project phase 5 climate model runs that shows large increases in cloud water path and surface cloud longwave forcing in warmer climates, suggest that the "lapse rate feedback" in simulations of anthropogenic climate change may be related to the influence of low clouds on the stratification of the lower troposphere. The results also indicate that optically thick stratus cloud decks could help to maintain frost-free winter continental interiors in equable climates.

Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming

PubMed Central

Cronin, Timothy W.; Tziperman, Eli

2015-01-01

High-latitude continents have warmed much more rapidly in recent decades than the rest of the globe, especially in winter, and the maintenance of warm, frost-free conditions in continental interiors in winter has been a long-standing problem of past equable climates. We use an idealized single-column atmospheric model across a range of conditions to study the polar night process of air mass transformation from high-latitude maritime air, with a prescribed initial temperature profile, to much colder high-latitude continental air. We find that a low-cloud feedback—consisting of a robust increase in the duration of optically thick liquid clouds with warming of the initial state—slows radiative cooling of the surface and amplifies continental warming. This low-cloud feedback increases the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature, effectively suppressing Arctic air formation. The time it takes for the surface air temperature to drop below freezing increases nonlinearly to ∼10 d for initial maritime surface air temperatures of 20 °C. These results, supplemented by an analysis of Coupled Model Intercomparison Project phase 5 climate model runs that shows large increases in cloud water path and surface cloud longwave forcing in warmer climates, suggest that the “lapse rate feedback” in simulations of anthropogenic climate change may be related to the influence of low clouds on the stratification of the lower troposphere. The results also indicate that optically thick stratus cloud decks could help to maintain frost-free winter continental interiors in equable climates. PMID:26324919

Response of the global surface ozone distribution to Northern Hemisphere sea surface temperature changes: implications for long-range transport

NASA Astrophysics Data System (ADS)

Yi, Kan; Liu, Junfeng; Ban-Weiss, George; Zhang, Jiachen; Tao, Wei; Cheng, Yanli; Tao, Shu

2017-07-01

The response of surface ozone (O3) concentrations to basin-scale warming and cooling of Northern Hemisphere oceans is investigated using the Community Earth System Model (CESM). Idealized, spatially uniform sea surface temperature (SST) anomalies of ±1 °C are individually superimposed onto the North Pacific, North Atlantic, and North Indian oceans. Our simulations suggest large seasonal and regional variability in surface O3 in response to SST anomalies, especially in the boreal summer. The responses of surface O3 associated with basin-scale SST warming and cooling have similar magnitude but are opposite in sign. Increasing the SST by 1 °C in one of the oceans generally decreases the surface O3 concentrations from 1 to 5 ppbv. With fixed emissions, SST increases in a specific ocean basin in the Northern Hemisphere tend to increase the summertime surface O3 concentrations over upwind regions, accompanied by a widespread reduction over downwind continents. We implement the integrated process rate (IPR) analysis in CESM and find that meteorological O3 transport in response to SST changes is the key process causing surface O3 perturbations in most cases. During the boreal summer, basin-scale SST warming facilitates the vertical transport of O3 to the surface over upwind regions while significantly reducing the vertical transport over downwind continents. This process, as confirmed by tagged CO-like tracers, indicates a considerable suppression of intercontinental O3 transport due to increased tropospheric stability at lower midlatitudes induced by SST changes. Conversely, the responses of chemical O3 production to regional SST warming can exert positive effects on surface O3 levels over highly polluted continents, except South Asia, where intensified cloud loading in response to North Indian SST warming depresses both the surface air temperature and solar radiation, and thus photochemical O3 production. Our findings indicate a robust linkage between basin-scale SST variability and continental surface O3 pollution, which should be considered in regional air quality management.

Sources of Uncertainty and the Interpretation of Short-Term Fluctuations

NASA Astrophysics Data System (ADS)

Lewandowsky, S.; Risbey, J.; Cowtan, K.; Rahmstorf, S.

2016-12-01

The alleged significant slowdown in global warming during the first decade of the 21st century, and the appearance of a discrepancy between models and observations, has attracted considerable research attention. We trace the history of this research and show how its conclusions were shaped by several sources of uncertainty and ambiguity about models and observations. We show that as those sources of uncertainty were gradually eliminated by further research, insufficient evidence remained to infer any discrepancy between models and observations or a significant slowing of warming. Specifically, we show that early research had to contend with uncertainties about coverage biases in the global temperature record and biases in the sea surface temperature observations which turned out to have exaggerated the extent of slowing. In addition, uncertainties in the observed forcings were found to have exaggerated the mismatch between models and observations. Further sources of uncertainty that were ultimately eliminated involved the use of incommensurate sea surface temperature data between models and observations and a tacit interpretation of model projections as predictions or forecasts. After all those sources of uncertainty were eliminated, the most recent research finds little evidence for an unusual slowdown or a discrepancy between models and observations. We discuss whether these different kinds of uncertainty could have been anticipated or managed differently, and how one can apply those lessons to future short-term fluctuations in warming.

Global temperature definition affects achievement of long-term climate goals

NASA Astrophysics Data System (ADS)

Richardson, Mark; Cowtan, Kevin; Millar, Richard J.

2018-05-01

The Paris Agreement on climate change aims to limit ‘global average temperature’ rise to ‘well below 2 °C’ but reported temperature depends on choices about how to blend air and water temperature data, handle changes in sea ice and account for regions with missing data. Here we use CMIP5 climate model simulations to estimate how these choices affect reported warming and carbon budgets consistent with the Paris Agreement. By the 2090s, under a low-emissions scenario, modelled global near-surface air temperature rise is 15% higher (5%–95% range 6%–21%) than that estimated by an approach similar to the HadCRUT4 observational record. The difference reduces to 8% with global data coverage, or 4% with additional removal of a bias associated with changing sea-ice cover. Comparison of observational datasets with different data sources or infilling techniques supports our model results regarding incomplete coverage. From high-emission simulations, we find that a HadCRUT4 like definition means higher carbon budgets and later exceedance of temperature thresholds, relative to global near-surface air temperature. 2 °C warming is delayed by seven years on average, to 2048 (2035–2060), and CO2 emissions budget for a >50% chance of <2 °C warming increases by 67 GtC (246 GtCO2).

Rapid warming of the world's lakes: Interdecadal variability and long-term trends from 1910-2009 using in situ and remotely sensed data

NASA Astrophysics Data System (ADS)

Lenters, J. D.; Read, J. S.; Sharma, S.; O'Reilly, C.; Hampton, S. E.; Gray, D.; McIntyre, P. B.; Hook, S. J.; Schneider, P.; Soylu, M. E.; Barabás, N.; Lofton, D. D.

2014-12-01

Global and regional changes in climate have important implications for terrestrial and aquatic ecosystems. Recent studies, for example, have revealed significant warming of inland water bodies throughout the world. To better understand the global patterns, physical mechanisms, and ecological implications of lake warming, an initiative known as the "Global Lake Temperature Collaboration" (GLTC) was started in 2010, with the objective of compiling and analyzing lake temperature data from numerous satellite and in situ records dating back at least 20-30 years. The GLTC project has now assembled data from over 300 lakes, with some in situ records extending back more than 100 years. Here, we present an analysis of the long-term warming trends, interdecadal variability, and a direct comparison between in situ and remotely sensed lake surface temperature for the 3-month summer period July-September (January-March for some lakes). The overall results show consistent, long-term trends of increasing summer-mean lake surface temperature across most but not all sites. Lakes with especially long records show accelerated warming in the most recent two to three decades, with almost half of the lakes warming at rates in excess of 0.5 °C per decade during the period 1985-2009, and a few even exceeding 1.0 °C per decade. Both satellite and in situ data show a similar distribution of warming trends, and a direct comparison at lake sites that have both types of data reveals a close correspondence in mean summer water temperature, interannual variability, and long-term trends. Finally, we examine standardized lake surface temperature anomalies across the full 100-year period (1910-2009), and in conjunction with similar timeseries of air temperature. The results reveal a close correspondence between summer air temperature and lake surface temperature on interannual and interdecadal timescales, but with many lakes warming more rapidly than the ambient air temperature over 25- to 100-year periods.

The ocean's role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing

PubMed Central

Marshall, John; Armour, Kyle C.; Scott, Jeffery R.; Kostov, Yavor; Hausmann, Ute; Ferreira, David; Shepherd, Theodore G.; Bitz, Cecilia M.

2014-01-01

In recent decades, the Arctic has been warming and sea ice disappearing. By contrast, the Southern Ocean around Antarctica has been (mainly) cooling and sea-ice extent growing. We argue here that interhemispheric asymmetries in the mean ocean circulation, with sinking in the northern North Atlantic and upwelling around Antarctica, strongly influence the sea-surface temperature (SST) response to anthropogenic greenhouse gas (GHG) forcing, accelerating warming in the Arctic while delaying it in the Antarctic. Furthermore, while the amplitude of GHG forcing has been similar at the poles, significant ozone depletion only occurs over Antarctica. We suggest that the initial response of SST around Antarctica to ozone depletion is one of cooling and only later adds to the GHG-induced warming trend as upwelling of sub-surface warm water associated with stronger surface westerlies impacts surface properties. We organize our discussion around ‘climate response functions’ (CRFs), i.e. the response of the climate to ‘step’ changes in anthropogenic forcing in which GHG and/or ozone-hole forcing is abruptly turned on and the transient response of the climate revealed and studied. Convolutions of known or postulated GHG and ozone-hole forcing functions with their respective CRFs then yield the transient forced SST response (implied by linear response theory), providing a context for discussion of the differing warming/cooling trends in the Arctic and Antarctic. We speculate that the period through which we are now passing may be one in which the delayed warming of SST associated with GHG forcing around Antarctica is largely cancelled by the cooling effects associated with the ozone hole. By mid-century, however, ozone-hole effects may instead be adding to GHG warming around Antarctica but with diminished amplitude as the ozone hole heals. The Arctic, meanwhile, responding to GHG forcing but in a manner amplified by ocean heat transport, may continue to warm at an accelerating rate. PMID:24891392

Understanding the El Niño-like Oceanic Response in the Tropical Pacific to Global Warming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Yiyong; Lu, Jian; Liu, Fukai

The enhanced central and eastern Pacific SST warming and the associated ocean processes under global warming are investigated using the ocean component of the Community Earth System Model (CESM), Parallel Ocean Program version 2 (POP2). The tropical SST warming pattern in the coupled CESM can be faithfully reproduced by the POP2 forced with surface fluxes computed using the aerodynamic bulk formula. By prescribing the wind stress and/or wind speed through the bulk formula, the effects of wind stress change and/or the wind-evaporation-SST (WES) feedback are isolated and their linearity is evaluated in this ocean-alone setting. Result shows that, although themore » weakening of the equatorial easterlies contributes positively to the El Niño-like SST warming, 80% of which can be simulated by the POP2 without considering the effects of wind change in both mechanical and thermodynamic fluxes. This result points to the importance of the air-sea thermal interaction and the relative feebleness of the ocean dynamical process in the El Niño-like equatorial Pacific SST response to global warming. On the other hand, the wind stress change is found to play a dominant role in the oceanic response in the tropical Pacific, accounting for most of the changes in the equatorial ocean current system and thermal structures, including the weakening of the surface westward currents, the enhancement of the near-surface stratification and the shoaling of the equatorial thermocline. Interestingly, greenhouse gas warming in the absence of wind stress change and WES feedback also contributes substantially to the changes at the subsurface equatorial Pacific. Further, this warming impact can be largely replicated by an idealized ocean experiment forced by a uniform surface heat flux, whereby, arguably, a purest form of oceanic dynamical thermostat is revealed.« less

The ocean's role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing.

PubMed

Marshall, John; Armour, Kyle C; Scott, Jeffery R; Kostov, Yavor; Hausmann, Ute; Ferreira, David; Shepherd, Theodore G; Bitz, Cecilia M

2014-07-13

In recent decades, the Arctic has been warming and sea ice disappearing. By contrast, the Southern Ocean around Antarctica has been (mainly) cooling and sea-ice extent growing. We argue here that interhemispheric asymmetries in the mean ocean circulation, with sinking in the northern North Atlantic and upwelling around Antarctica, strongly influence the sea-surface temperature (SST) response to anthropogenic greenhouse gas (GHG) forcing, accelerating warming in the Arctic while delaying it in the Antarctic. Furthermore, while the amplitude of GHG forcing has been similar at the poles, significant ozone depletion only occurs over Antarctica. We suggest that the initial response of SST around Antarctica to ozone depletion is one of cooling and only later adds to the GHG-induced warming trend as upwelling of sub-surface warm water associated with stronger surface westerlies impacts surface properties. We organize our discussion around 'climate response functions' (CRFs), i.e. the response of the climate to 'step' changes in anthropogenic forcing in which GHG and/or ozone-hole forcing is abruptly turned on and the transient response of the climate revealed and studied. Convolutions of known or postulated GHG and ozone-hole forcing functions with their respective CRFs then yield the transient forced SST response (implied by linear response theory), providing a context for discussion of the differing warming/cooling trends in the Arctic and Antarctic. We speculate that the period through which we are now passing may be one in which the delayed warming of SST associated with GHG forcing around Antarctica is largely cancelled by the cooling effects associated with the ozone hole. By mid-century, however, ozone-hole effects may instead be adding to GHG warming around Antarctica but with diminished amplitude as the ozone hole heals. The Arctic, meanwhile, responding to GHG forcing but in a manner amplified by ocean heat transport, may continue to warm at an accelerating rate.

Diagnosing Warm Frontal Cloud Formation in a GCM: A Novel Approach Using Conditional Subsetting

NASA Technical Reports Server (NTRS)

Booth, James F.; Naud, Catherine M.; DelGenio, Anthony D.

2013-01-01

This study analyzes characteristics of clouds and vertical motion across extratropical cyclone warm fronts in the NASA Goddard Institute for Space Studies general circulation model. The validity of the modeled clouds is assessed using a combination of satellite observations from CloudSat, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E), and the NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis. The analysis focuses on developing cyclones, to test the model's ability to generate their initial structure. To begin, the extratropical cyclones and their warm fronts are objectively identified and cyclone-local fields are mapped into a vertical transect centered on the surface warm front. To further isolate specific physics, the cyclones are separated using conditional subsetting based on additional cyclone-local variables, and the differences between the subset means are analyzed. Conditional subsets are created based on 1) the transect clouds and 2) vertical motion; 3) the strength of the temperature gradient along the warm front, as well as the storm-local 4) wind speed and 5) precipitable water (PW). The analysis shows that the model does not generate enough frontal cloud, especially at low altitude. The subsetting results reveal that, compared to the observations, the model exhibits a decoupling between cloud formation at high and low altitudes across warm fronts and a weak sensitivity to moisture. These issues are caused in part by the parameterized convection and assumptions in the stratiform cloud scheme that are valid in the subtropics. On the other hand, the model generates proper covariability of low-altitude vertical motion and cloud at the warm front and a joint dependence of cloudiness on wind and PW.

Conservation Planning for Coral Reefs Accounting for Climate Warming Disturbances

PubMed Central

Magris, Rafael A.; Heron, Scott F.; Pressey, Robert L.

2015-01-01

Incorporating warming disturbances into the design of marine protected areas (MPAs) is fundamental to developing appropriate conservation actions that confer coral reef resilience. We propose an MPA design approach that includes spatially- and temporally-varying sea-surface temperature (SST) data, integrating both observed (1985–2009) and projected (2010–2099) time-series. We derived indices of acute (time under reduced ecosystem function following short-term events) and chronic thermal stress (rate of warming) and combined them to delineate thermal-stress regimes. Coral reefs located on the Brazilian coast were used as a case study because they are considered a conservation priority in the southwestern Atlantic Ocean. We show that all coral reef areas in Brazil have experienced and are projected to continue to experience chronic warming, while acute events are expected to increase in frequency and intensity. We formulated quantitative conservation objectives for regimes of thermal stress. Based on these objectives, we then evaluated if/how they are achieved in existing Brazilian MPAs and identified priority areas where additional protection would reinforce resilience. Our results show that, although the current system of MPAs incorporates locations within some of our thermal-stress regimes, historical and future thermal refugia along the central coast are completely unprotected. Our approach is applicable to other marine ecosystems and adds to previous marine planning for climate change in two ways: (i) by demonstrating how to spatially configure MPAs that meet conservation objectives for warming disturbance using spatially- and temporally-explicit data; and (ii) by strategically allocating different forms of spatial management (MPA types) intended to mitigate warming impacts and also enhance future resistance to climate warming. PMID:26535586

Drylands face potential threat under 2 °C global warming target

NASA Astrophysics Data System (ADS)

Huang, Jianping; Yu, Haipeng; Dai, Aiguo; Wei, Yun; Kang, Litai

2017-06-01

The Paris Agreement aims to limit global mean surface warming to less than 2 °C relative to pre-industrial levels. However, we show this target is acceptable only for humid lands, whereas drylands will bear greater warming risks. Over the past century, surface warming over global drylands (1.2-1.3 °C) has been 20-40% higher than that over humid lands (0.8-1.0 °C), while anthropogenic CO2 emissions generated from drylands (~230 Gt) have been only ~30% of those generated from humid lands (~750 Gt). For the twenty-first century, warming of 3.2-4.0 °C (2.4-2.6 °C) over drylands (humid lands) could occur when global warming reaches 2.0 °C, indicating ~44% more warming over drylands than humid lands. Decreased maize yields and runoff, increased long-lasting drought and more favourable conditions for malaria transmission are greatest over drylands if global warming were to rise from 1.5 °C to 2.0 °C. Our analyses indicate that ~38% of the world's population living in drylands would suffer the effects of climate change due to emissions primarily from humid lands. If the 1.5 °C warming limit were attained, the mean warming over drylands could be within 3.0 °C therefore it is necessary to keep global warming within 1.5 °C to prevent disastrous effects over drylands.

Paleoecology, Biostratigraphy, and Response of Calcareous Nannoplankton Communities to Climate Fluctuations during the Late Oligocene in the Tropics

NASA Astrophysics Data System (ADS)

Aljahdali, M. H.; Wise, S. W.

2015-12-01

The earliest Oligocene is considered the time that the Cenozoic icehouse world was initiated when the Antarctic continental ice sheet first reached sea level. Subsequently during the Oligocene, climate then fluctuated between glacial (Oi) and warming events as recorded by stable isotopes. Relatively little is known about the paleoecological response of calcareous nannoplankton at low latitudes during these climate deteriorations. Here we investigate the biotic response along with the stable-isotope (δ18O and δ13C) record and multivariate analyses from four ODP and IODP sites cored in three oceans along the tropical belt through strata 24-30 Ma in age. Within this time frame, two major climatic shifts occurred, the Oi-2b glacial event and the Late Oligocene Warming Event (LOWE). During the Oi-events (26.5-30 Ma) temperate-water taxa associated with eutrophic taxa dominated the overall assemblage, suggesting that relatively cooler water rich in nutrients invaded the tropical region. In contrast, during the LOWE (24-26.5 Ma), a major turnover between temperate-water taxa and warm-water taxa occurred when the surface waters became warm and oligotrophic in nature. Additionally, several increases in both abundance and size were recorded through the upper Oligocene including increased abundance in Sphenolithus predistentus, a major biostratigraphic marker in the upper Oligocene, and increased size in S. moriformis. Moreover, a new additional major biostratigraphic event in the upper Oligocene was recorded; Crassidiscus backmanii shows a very short range at low latitudes. These paleoecological responses can be utilized to construct a detailed global late Oligocene biostratigraphy throughout the tropics.

An atmospheric origin of the multi-decadal bipolar seesaw.

PubMed

Wang, Zhaomin; Zhang, Xiangdong; Guan, Zhaoyong; Sun, Bo; Yang, Xin; Liu, Chengyan

2015-03-10

A prominent feature of recent climatic change is the strong Arctic surface warming that is contemporaneous with broad cooling over much of Antarctica and the Southern Ocean. Longer global surface temperature observations suggest that this contrasting pole-to-pole change could be a manifestation of a multi-decadal interhemispheric or bipolar seesaw pattern, which is well correlated with the North Atlantic sea surface temperature variability, and thus generally hypothesized to originate from Atlantic meridional overturning circulation oscillations. Here, we show that there is an atmospheric origin for this seesaw pattern. The results indicate that the Southern Ocean surface cooling (warming) associated with the seesaw pattern is attributable to the strengthening (weakening) of the Southern Hemisphere westerlies, which can be traced to Northern Hemisphere and tropical tropospheric warming (cooling). Antarctic ozone depletion has been suggested to be an important driving force behind the recently observed increase in the Southern Hemisphere's summer westerly winds; our results imply that Northern Hemisphere and tropical warming may have played a triggering role at an stage earlier than the first detectable Antarctic ozone depletion, and enhanced Antarctic ozone depletion through decreasing the lower stratospheric temperature.

Convective and radiative components of wind chill in sheep: Estimation from meteorological records

NASA Astrophysics Data System (ADS)

Brown, D.; Mount, L. E.

1987-06-01

Wind chill is defined as the excess of sensible heat loss over what would occur at zero wind speed with other conditions unchanged. Wind chill can be broken down into a part that is determined by air temperature and a radiative part that comprises wind-dependent effects on additional long-wave radiative exchange and on solar radiation (by reducing solar warming). Radiative exchange and gain from solar radiation are affected by changes that are produced by wind in both surface and fleece insulations. Coefficients are derived for (a) converting the components of sensible heat exchange (air-temperature-dependent including both convective and associated long-wave radiative, additional long-wave radiative and solar) into the components of the total heat loss that are associated with wind and (b) for calculating equivalent air temperature changes. The coefficients contain terms only in wind speed, wetting of the fleece and fleece depth; these determine the external insulation. Calculation from standard meteorological records, using Plymouth and Aberdeen in 1973 as examples, indicate that in April September 1973 at Plymouth reduction in effective solar warming constituted 28% of the 24-h total wind chill, and 7% in the other months of the year combined; at Aberdeen the corresponding percentages were 25% and 6%. Mean hour-of-day estimates for the months of April and October showed that at midday reduction in solar warming due to wind rose to the order of half the air-temperature-dependent component of wind chill, with a much smaller effect in January. For about six hours at midday in July reduction in solar warming due to wind was similar in magnitude to the air-temperature-dependent component. It is concluded that realistic estimates of wind chill cannot be obtained unless the effect of solar radiation is taken into account. Failure to include solar radiation results not only in omitting solar warming but also in omitting the effects of wind in reducing that warming. The exchange of sensible (non-evaporative) heat loss between a homeothermic animal and its environment can be divided into two parts: one part is due to the temperature difference between the animal and the surrounding air, and the other part is due to additional long-wave radiative exchange between animal and environment and to solar radiation. Both parts of the heat exchange are determined in magnitude by the animal's thermal insulation, which is itself affected by windspeed and wetting. Wind diminishes as animal's external insulation, so increasing heat loss under all conditions when the air temperature is lower than the animal's surface temperature: this effect is termed wind chill. Wind chill has previously been investigated more commonly in relation to man (Burton an Edholm, 1955; Smithson and Baldwin, 1978; Mumford, 1979; Baldwin and Smithson, 1979). This paper is concerned with the separate contributions to wind chill calculated for sheep that can be associated with convective and radiative heat exchanges.

Global Warming - Are We on Thin Ice?

NASA Technical Reports Server (NTRS)

Tucker, Compton J.

2007-01-01

The evidence for global warming is very conclusive for the past 400-500 years. Prior to the 16th century, proxy surface temperature data are regionally good but lack a global distribution. The speaker will review surface temperature reconstruction based upon ice cores, coral cores, tree rings, deep sea sediments, and bore holes and discuss the controversy surrounding global warming. This will be contrasted with the excellent data we have from the satellite era of earth observations the past 30+ years that enables the quantitative study of climate across earth science disciplines.

Sensitivity of the Tropical Pacific Ocean to Precipitation Induced Freshwater Flux

NASA Technical Reports Server (NTRS)

Yang, Song; Lau, K.-M.; Schopf, Paul S.

1999-01-01

We have performed a series of experiments using an ocean model to study the sensitivity of tropical Pacific Ocean to variations in precipitation induced freshwater fluxes. Variations in these fluxes arise from natural causes on all time scales. In addition, estimates of these fluxes are uncertain because of differences among measurement techniques. The model used is a quasi-isopycnal model, covering the Pacific from 40 S to 40 N. The surface forcing is constructed from observed wind stress, evaporation, precipitation, and surface temperature (SST) fields. The heat flux is produced with an iterative technique so as to maintain the model close to the observed climatology, but with only a weak damping to that climatology. Climatological estimates of evaporation are combined with various estimates of precipitation to determine the net surface freshwater flux. Results indicate that increased freshwater input decreases salinity as expected, but increases temperatures in the upper ocean. Using the freshwater flux estimated from the Microwave Sounding Unit leads to a warming of up to 0.6 C in the western Pacific over a case with zero net freshwater flux. SST is sensitive to the discrepancies among different precipitation observations, with root-mean-square differences in SST on the order of 0.2-0.3 C. The change in SST is more pronounced in the eastern Pacific, with differences of over 1 C found among the various precipitation products. Interannual variation in precipitation during El Nino events leads to increased warming. During the winter of 1982-83, freshwater flux accounts for about 0.4 C (approximately 10-15% of the maximum warming) of the surface warming in the central-eastern Pacific. Thus, the error of SST caused by the discrepancies in precipitation products is more than half of the SST anomaly produced by the interannual variability of observed precipitation. Further experiments, in which freshwater flux anomalies are imposed in the western, central, and eastern Pacific, show that the influence of net freshwater flux is also spatially dependent. The imposition of freshwater flux in the far western Pacific leads to a trapping of salinity anomaly to the surface layers near the equator. An identical flux imposed in the central Pacific produces deeper and off-equatorial salinity anomalies. The contrast between these two simulations is consistent with other simulations of the western Pacific barrier layer information.

Quantifying uncertainties of permafrost carbon-climate feedbacks

NASA Astrophysics Data System (ADS)

Burke, Eleanor J.; Ekici, Altug; Huang, Ye; Chadburn, Sarah E.; Huntingford, Chris; Ciais, Philippe; Friedlingstein, Pierre; Peng, Shushi; Krinner, Gerhard

2017-06-01

The land surface models JULES (Joint UK Land Environment Simulator, two versions) and ORCHIDEE-MICT (Organizing Carbon and Hydrology in Dynamic Ecosystems), each with a revised representation of permafrost carbon, were coupled to the Integrated Model Of Global Effects of climatic aNomalies (IMOGEN) intermediate-complexity climate and ocean carbon uptake model. IMOGEN calculates atmospheric carbon dioxide (CO2) and local monthly surface climate for a given emission scenario with the land-atmosphere CO2 flux exchange from either JULES or ORCHIDEE-MICT. These simulations include feedbacks associated with permafrost carbon changes in a warming world. Both IMOGEN-JULES and IMOGEN-ORCHIDEE-MICT were forced by historical and three alternative future-CO2-emission scenarios. Those simulations were performed for different climate sensitivities and regional climate change patterns based on 22 different Earth system models (ESMs) used for CMIP3 (phase 3 of the Coupled Model Intercomparison Project), allowing us to explore climate uncertainties in the context of permafrost carbon-climate feedbacks. Three future emission scenarios consistent with three representative concentration pathways were used: RCP2.6, RCP4.5 and RCP8.5. Paired simulations with and without frozen carbon processes were required to quantify the impact of the permafrost carbon feedback on climate change. The additional warming from the permafrost carbon feedback is between 0.2 and 12 % of the change in the global mean temperature (ΔT) by the year 2100 and 0.5 and 17 % of ΔT by 2300, with these ranges reflecting differences in land surface models, climate models and emissions pathway. As a percentage of ΔT, the permafrost carbon feedback has a greater impact on the low-emissions scenario (RCP2.6) than on the higher-emissions scenarios, suggesting that permafrost carbon should be taken into account when evaluating scenarios of heavy mitigation and stabilization. Structural differences between the land surface models (particularly the representation of the soil carbon decomposition) are found to be a larger source of uncertainties than differences in the climate response. Inertia in the permafrost carbon system means that the permafrost carbon response depends on the temporal trajectory of warming as well as the absolute amount of warming. We propose a new policy-relevant metric - the frozen carbon residence time (FCRt) in years - that can be derived from these complex land surface models and used to quantify the permafrost carbon response given any pathway of global temperature change.

Causes of global mean surface temperature slowdowns, trends and variations from months to a century, 1891-2015

NASA Astrophysics Data System (ADS)

Folland, C. K.; Boucher, O.; Colman, A.; Parker, D. E.

2017-12-01

The recent slowdown in the warming of global mean surface temperature (GST) has highlighted the influences of natural variability. This talk discusses reconstructions of the variations of GST down to the monthly time scale since 1891 using monthly forcing data. We show that most of the variations in annual, and to some extent sub-annual, GST since 1891 can be reproduced skillfully from known forcing factors external and internal to the climate system. This includes the slowdown in warming over about 1998-2013 where reconstruction skill is particularly high down to the multi-monthly time scale. The relative contributions of the several key forcing factors to GST continually vary, but most of the net warming since 1891 is reconstructed to be attributable to the net forcing due to increasing greenhouse gases and anthropogenic aerosols. Separate analyses are carried out for three periods of GST slowdown:- 1896-1910, 1941-1976, together with 1998-2013 and some of its sub periods. We also study two periods where strong warming occurred, 1911-1940 and 1977-1997. Comparisons are made with the skill of average GST provided by 40 CMIP5 models. In the recent 1998-2013 slowdown, TSI forcing appears to have caused significant cooling, particularly over 2001-2010. This is additional to well documented cooling effects of an increased frequency of La Nina events, a negative Interdecadal Pacific Oscillation and some increases in volcanic forcing. Although there are short-term features of the GST curve since 1891 that cannot be fully explained, the most serious disagreements between the reconstructions and observations occur in the Second World War, especially in 1944-1945. Here observed near worldwide SSTs may be biased significantly too warm. Despite this, our generally high reconstruction skill is consistent with a good understanding of the multiple causes of observed GST variations and the general veracity of the GST record since 1891.

Attributing extreme precipitation in the Black Sea region to sea surface warming

NASA Astrophysics Data System (ADS)

Meredith, Edmund; Semenov, Vladimir; Maraun, Douglas; Park, Wonsun; Chernokulsky, Alexander

2016-04-01

Higher sea surface temperatures (SSTs) warm and moisten the overlying atmosphere, increasing the low-level atmospheric instability, the moisture available to precipitating systems and, hence, the potential for intense convective systems. Both the Mediterranean and Black Sea regions have seen a steady increase in summertime SSTs since the early 1980s, by over 2 K in places. This raises the question of how this SST increase has affected convective precipitation extremes in the region, and through which mechanisms any effects are manifested. In particular, the Black Sea town of Krymsk suffered an unprecedented precipitation extreme in July 2012, which may have been influenced by Black Sea warming, causing over 170 deaths. To address this question, we adopt two distinct modelling approaches to event attribution and compare their relative merits. In the first, we use the traditional probabilistic event attribution approach involving global climate model ensembles representative of the present and a counterfactual past climate where regional SSTs have not increased. In the second, we use the conditional event attribution approach, taking the 2012 Krymsk precipitation extreme as a showcase example. Under the second approach, we carry out ensemble sensitivity experiments of the Krymsk event at convection-permitting resolution with the WRF regional model, and test the sensitivity of the event to a range of SST forcings. Both experiments show the crucial role of recent Black Sea warming in amplifying the 2012 Krymsk precipitation extreme. In the conditional event attribution approach, though, the explicit simulation of convective processes provides detailed insight into the physical mechanisms behind the extremeness of the event, revealing the dominant role of dynamical (i.e. static stability and vertical motions) over thermodynamical (i.e. increased atmospheric moisture) changes. Additionally, the wide range of SST states tested in the regional setup, which would be infeasible under the global modelling approach, reveal that the intensity of the Krymsk event responds highly nonlinearly to Black Sea warming and suggests a role for regional SST thresholds in more intense coastal convective extremes.

Forcing of global ocean ice models using an atmospheric boundary layer model: assessing consequences for the simulation of the AMOC

NASA Astrophysics Data System (ADS)

Abel, R.; Boning, C. W.

2016-02-01

Current practice in ocean-only model simulations is to force the ocean with a prescribed atmospheric state using bulk formulations. This practice provides a strong thermal restoring to the surface ocean with a typical time-scale of one month. In the real ocean a positive feedback (salinity advection) and a negative feedback (temperature advection) are associated with the Atlantic Meridional Overturning Circulation (AMOC). The surface branch of the AMOC transports warm and salty (relative to the mean conditions) to the subpolar North Atlantic and mix with the near-surface waters. A strong AMOC would therefore warm the subpolar North Atlantic, decrease deep water formation and also reduce AMOC strength (negative feedback). This negative feedback is diminished due to the surface forcing formulation and makes the system excessively sensitive to details in the freshwater fluxes . Instead, additional and unrealistic Sea Surface Salinity (SSS) restoring is applied. There have been several suggestions during the last 20 years for at least partially alleviating the problem. This includes some simplified model of the atmospheric mixed layer (AML) (CheapAML; Deremble et al., 2013) with prescribed winds which allows some feedback of SST anomalies on the near-surface air temperature and humidity needed to calculate the turbulent surface fluxes. We show that if the turbulent heat fluxes are modelled by the simple AML model net-fluxes get more realistic. Commonly ocean models experience an AMOC slowdown if SSS restoring is turned off. In the new system (ORCA05 with turbulent fluxes from CheapAML) this slowdown can be eliminated.

The geological and climatological case for a warmer and wetter early Mars

NASA Astrophysics Data System (ADS)

Ramirez, Ramses M.; Craddock, Robert A.

2018-04-01

The climate of early Mars remains a topic of intense debate. Ancient terrains preserve landscapes consistent with stream channels, lake basins and possibly even oceans, and thus the presence of liquid water flowing on the Martian surface 4 billion years ago. However, despite the geological evidence, determining how long climatic conditions supporting liquid water lasted remains uncertain. Climate models have struggled to generate sufficiently warm surface conditions given the faint young Sun—even assuming a denser early atmosphere. A warm climate could have potentially been sustained by supplementing atmospheric CO2 and H2O warming with either secondary greenhouse gases or clouds. Alternatively, the Martian climate could have been predominantly cold and icy, with transient warming episodes triggered by meteoritic impacts, volcanic eruptions, methane bursts or limit cycles. Here, we argue that a warm and semi-arid climate capable of producing rain is most consistent with the geological and climatological evidence.

Physical mechanisms of spring and summertime drought related with the global warming over the northern America

NASA Astrophysics Data System (ADS)

Choi, W.; Kim, K. Y.

2017-12-01

Drought during the growing season (spring through summer) is severe natural hazard in the large cropland over the northern America. It is important to understand how the drought is related with the global warming and how it will change in the future. This study aims to investigate the physical mechanism of global warming impact on the spring and summertime drought over the northern America using Cyclostationary Empirical Orthogonal Function (CSEOF) analysis. The Northern Hemisphere surface warming, the most dominant mode of the surface air temperature, has resulted in decreased relative humidity and precipitation over the mid-latitude region of North America. For the viewpoint of atmospheric water demand, soil moisture and evaporation have also decreased significantly, exacerbating vulnerability of drought. These consistent features of changes in water demand and supply related with the global warming can provide a possibility of credible insight for future drought change.

Intraseasonal sea surface warming in the western Indian Ocean by oceanic equatorial Rossby waves

NASA Astrophysics Data System (ADS)

Rydbeck, Adam V.; Jensen, Tommy G.; Nyadjro, Ebenezer S.

2017-05-01

A novel process is identified whereby equatorial Rossby (ER) waves maintain warm sea surface temperature (SST) anomalies against cooling by processes related to atmospheric convection in the western Indian Ocean. As downwelling ER waves enter the western Indian Ocean, SST anomalies of +0.15°C develop near 60°E. These SST anomalies are hypothesized to stimulate convective onset of the Madden-Julian Oscillation. The upper ocean warming that manifests in response to downwelling ER waves is examined in a mixed layer heat budget using observational and reanalysis products, respectively. In the heat budget, horizontal advection is the leading contributor to warming, in part due to an equatorial westward jet of 80 cm s-1 associated with downwelling ER waves. When anomalous currents associated with ER waves are removed in the budget, the warm intraseasonal temperature anomaly in the western Indian Ocean is eliminated in observations and reduced by 55% in reanalysis.

Deep peat warming increases surface methane and carbon dioxide emissions in a black spruce-dominated ombrotrophic bog.

PubMed

Gill, Allison L; Giasson, Marc-André; Yu, Rieka; Finzi, Adrien C

2017-12-01

Boreal peatlands contain approximately 500 Pg carbon (C) in the soil, emit globally significant quantities of methane (CH 4 ), and are highly sensitive to climate change. Warming associated with global climate change is likely to increase the rate of the temperature-sensitive processes that decompose stored organic carbon and release carbon dioxide (CO 2 ) and CH 4 . Variation in the temperature sensitivity of CO 2 and CH 4 production and increased peat aerobicity due to enhanced growing-season evapotranspiration may alter the nature of peatland trace gas emission. As CH 4 is a powerful greenhouse gas with 34 times the warming potential of CO 2 , it is critical to understand how factors associated with global change will influence surface CO 2 and CH 4 fluxes. Here, we leverage the Spruce and Peatland Responses Under Changing Environments (SPRUCE) climate change manipulation experiment to understand the impact of a 0-9°C gradient in deep belowground warming ("Deep Peat Heat", DPH) on peat surface CO 2 and CH 4 fluxes. We find that DPH treatments increased both CO 2 and CH 4 emission. Methane production was more sensitive to warming than CO 2 production, decreasing the C-CO 2 :C-CH 4 of the respired carbon. Methane production is dominated by hydrogenotrophic methanogenesis but deep peat warming increased the δ 13 C of CH 4 suggesting an increasing contribution of acetoclastic methanogenesis to total CH 4 production with warming. Although the total quantity of C emitted from the SPRUCE Bog as CH 4 is <2%, CH 4 represents >50% of seasonal C emissions in the highest-warming treatments when adjusted for CO 2 equivalents on a 100-year timescale. These results suggest that warming in boreal regions may increase CH 4 emissions from peatlands and result in a positive feedback to ongoing warming. © 2017 John Wiley & Sons Ltd.

How does whole ecosystem warming of a peatland affect methane production and consumption?

NASA Astrophysics Data System (ADS)

Hopple, A.; Brunik, K.; Keller, J.; Pfeifer-Meister, L.; Woerndle, G.; Zalman, C.; Hanson, P.; Bridgham, S. D.

2017-12-01

Peatlands are among Earth's most important terrestrial ecosystems due to their massive soil carbon (C) stores and significant release of methane (CH4) into the atmosphere. Methane has a sustained-flux global warming potential 45-times greater than carbon dioxide (CO2), and the accuracy of Earth system model projections relies on our mechanistic understanding of peatland CH4 cycling in the context of environmental change. The objective of this study was to determine, under in situ conditions, how heating of the peat profile affects ecosystem-level anaerobic C cycling. We assessed the response of CO2 and CH4 production, as well as the anaerobic oxidation of CH4 (AOM), in a boreal peatland following 13 months of deep peat heating (DPH) and 16 months of subsequent whole-ecosystem warming (surface and deep heating; WEW) as part of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project in northern Minnesota, USA. The study uses a regression-based experimental design including 5 temperature treatments that warmed the entire 2 m peat profile from 0 to +9 °C above ambient temperature. Soil cores were collected at multiple depths (25-200 cm) from each experimental chamber at the SPRUCE site and anaerobically incubated at in situ temperatures for 1-2 weeks. Methane and CO2 production in surface peat were positively correlated with elevated temperature, but no consistent temperature response was found at depth (75-200 cm) following DPH. However, during WEW, we observed significant increases in both surface and deep peat methanogenesis with increasing temperature. Surface peat had greater CH4 production rates than deeper peat, implying that the increased CH4 emissions observed in the field were largely driven by surface peat warming. The CO2:CH4 ratio was inversely correlated with temperature across all depths following 16 months of WEW, indicating that the entire peat profile is becoming more methanogenic with warming. We also observed AOM throughout the whole peat profile, with the highest rates observed at the surface and initial data suggesting a positive correlation with increasing temperature. While SPRUCE will continue for many years, our initial results suggest that the vast C stores at depth in peatlands are minimally responsive to warming and any response will be driven largely by surface peat.

Seasonality of coastal upwelling trends under future warming scenarios along the southern limit of the canary upwelling system

NASA Astrophysics Data System (ADS)

Sousa, Magda Catarina; Alvarez, Ines; deCastro, Maite; Gomez-Gesteira, Moncho; Dias, João Miguel

2017-04-01

The Canary Upwelling Ecosystem (CUE) is one of the four most important upwelling sites around the world in terms of primary production, with coastal upwelling mostly a year-round phenomenon south of 30°N. Based on annual future projections, several previous studies indicated that global warming will intensify coastal upwelling in the northern region and will induce its weakening at the southernmost latitudes. However, analysis of historical data, showed that coastal upwelling depends on the length of the time series, the season, and even the database used. Thus, despite previous efforts, an overall detailed description of seasonal upwelling trends and their effects on sea surface temperature (SST) along the Canary coast over the 21st century remains unclear. To address this issue, several regional and global wind and SST climate models from CORDEX and CMIP5 projects for the period 1976-2099 were analyzed. This research provides new insights about coastal upwelling trends under future warming scenarios for the CUE, with results showing opposite patterns for upwelling index (UI) trends depending on the season. A weakening of the UI occurs from May to August all along the coast, whereas it increases from October to April. Analysis of SST trends reveals a general warming throughout the area, although the warming rate is considerably lower near the shore than at open ocean locations due to coastal upwelling effects. In addition, SST projections show higher warming rates from May to August than from October to April in response to the future decreasing trend in the UI during the summer months.

Non-additive effects of ocean acidification in combination with warming on the larval proteome of the Pacific oyster, Crassostrea gigas.

PubMed

Harney, Ewan; Artigaud, Sébastien; Le Souchu, Pierrick; Miner, Philippe; Corporeau, Charlotte; Essid, Hafida; Pichereau, Vianney; Nunes, Flavia L D

2016-03-01

Increasing atmospheric carbon dioxide results in ocean acidification and warming, significantly impacting marine invertebrate larvae development. We investigated how ocean acidification in combination with warming affected D-veliger larvae of the Pacific oyster Crassostrea gigas. Larvae were reared for 40h under either control (pH8.1, 20 °C), acidified (pH7.9, 20 °C), warm (pH8.1, 22 °C) or warm acidified (pH7.9, 22 °C) conditions. Larvae in acidified conditions were significantly smaller than in the control, but warm acidified conditions mitigated negative effects on size, and increased calcification. A proteomic approach employing two-dimensional electrophoresis (2-DE) was used to quantify proteins and relate their abundance to phenotypic traits. In total 12 differentially abundant spots were identified by nano-liquid chromatography-tandem mass spectrometry. These proteins had roles in metabolism, intra- and extra-cellular matrix formations, stress response, and as molecular chaperones. Seven spots responded to reduced pH, four to increased temperature, and six to acidification and warming. Reduced abundance of proteins such as ATP synthase and GAPDH, and increased abundance of superoxide dismutase, occurred when both pH and temperature changes were imposed, suggesting altered metabolism and enhanced oxidative stress. These results identify key proteins that may be involved in the acclimation of C. gigas larvae to ocean acidification and warming. Increasing atmospheric CO2 raises sea surface temperatures and results in ocean acidification, two climatic variables known to impact marine organisms. Larvae of calcifying species may be particularly at risk to such changing environmental conditions. The Pacific oyster Crassostrea gigas is ecologically and commercially important, and understanding its ability to acclimate to climate change will help to predict how aquaculture of this species is likely to be impacted. Modest, yet realistic changes in pH and/or temperature may be more informative of how populations will respond to contemporary climate change. We showed that concurrent acidification and warming mitigates the negative effects of pH alone on size of larvae, but proteomic analysis reveals altered patterns of metabolism and an increase in oxidative stress suggesting non-additive effects of the interaction between pH and temperature on protein abundance. Thus, even small changes in climate may influence development, with potential consequences later in life. Copyright © 2015 Elsevier B.V. All rights reserved.

Responses of Mean and Extreme Precipitation to Deforestation in the Maritime Continent

NASA Astrophysics Data System (ADS)

Chen, C. C.; Lo, M. H.; Yu, J. Y.

2017-12-01

Anthropogenic land use and land cover change, including tropical deforestation, could have substantial effects on local surface energy and water budgets, and thus on the atmospheric stability which may result in changes in precipitation. Maritime Continent has undergone severe deforestation in recent decades but has received less attention than Amazon or Congo rainforests. Therefore, this study is to decipher the precipitation response to deforestation in the Maritime Continent. We conduct deforestation experiments using Community Earth System Model (CESM) and through converting the tropical rainforest into grassland. The results show that deforestation in Maritime Continent leads to an increase in both mean temperature and mean precipitation. Moisture budget analysis indicates that the increase in precipitation is associated with the vertically integrated vertical moisture advection, especially the dynamic component (changes in convection). In addition, through moist static energy (MSE) budget analysis, we find the atmosphere among deforested areas become unstable owing to the combined effects of positive specific humidity anomalies at around 850 hPa and anomalous warming extended from the surface to 750 hPa. This instability will induce anomalous ascending motion, which could enhance the low-level moisture convergence, providing water vapor from the surrounding warm ocean. To further evaluate the precipitation response to deforestation, we examine the precipitation changes under La Niña events and global warming scenario using CESM Atmospheric Model Intercomparison Project (AMIP) simulations and Representative Concentration Pathway (RCP) 8.5 simulations. We find that the precipitation increase caused by deforestation in Maritime Continent is comparable in magnitude to that generated by either natural variability or global warming forcing. Besides the changes in mean precipitation, preliminary results show the extreme precipitation also increases. We will further explore how the extreme precipitation changes with the deforestation forcing.

An Intercomparison of Changes Associated with Earth's Lower Tropospheric Temperature Using Traditional and AMIP-Style Reanalyses

NASA Technical Reports Server (NTRS)

Marquardt-Collow, Allison B.; Bosilovich, Michael G.; Cullather, Richard I.

2017-01-01

Reanalyses have become an integral tool for evaluating regional and global climate variations, and an important component of this is modifications to the energy budget. Reductions in Arctic Sea ice extent has induced an albedo feedback, causing the Arctic to warm more rapidly than anywhere else in the world, referred to as "Arctic Amplification." This has been demonstrated by observations and numerous reanalyses, including the Modern Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2). However, the Arctic Amplification signal is non-existent in a ten member ensemble of the MERRA-2 Atmospheric Model Intercomparison Project (M2AMIP) simulations, using the same prescribed climate forcing, including Sea Surface Temperature (SST) and ice. An evaluation of the temperature tendency within the lower troposphere due to radiation, moisture, and dynamics as well as the surface energy budget in MERRA-2 and M2AMIP will demonstrate that despite identical prescribed SSTs and sea ice in both versions, enhanced warming in the Arctic in MERRA-2 is in response to the analysis increment tendency due to temperature observations. Furthermore, the role of boundary conditions, model biases and changes in observing systems on the Arctic Amplification signal will be assessed. Literature on the topic of Arctic Amplification demonstrates that the enhanced warming begins in the mid-1990s. Anomalously warm Arctic SST in the early time period of MERRA-2 can mute the trend in Arctic lower troposphere temperature without the constraint of observations in M2AMIP. Additionally, MERRA-2 uses three distinct datasets of SST and sea ice concentration, which also plays a role.

Radiative and Physiological Effects of Increased CO2: How Does This Interaction Affect Climate?

NASA Technical Reports Server (NTRS)

Bounoua, Lahouari

2011-01-01

Several climate models indicate that in a 2xCO2 environment, temperature and precipitation would increase and runoff would increase faster than precipitation. These models, however, did not allow the vegetation to increase its leaf density as a response to the physiological effects of increased CO2 and consequent changes in climate. Other assessments included these interactions but did not account for the vegetation downregulation to reduce plant's photosynthetic activity and as such resulted in a weak vegetation negative response. When we combine these interactions in climate simulations with 2xCO2, the associated increase in precipitation contributes primarily to increase evapotranspiration rather than surface runoff, consistent with observations, and results in an additional cooling effect not fully accounted for in previous 2xCO2 simulations. By accelerating the water cycle, this feedback slows but does not alleviate the projected warming, reducing the land surface warming by 0.6 C. Compared to previous studies, these results imply that long term negative feedback from CO2-induced increases in vegetation density could reduce temperature following a stabilization of CO2 concentration.

Unprecedented 2015/2016 Indo-Pacific Heat Transfer Speeds Up Tropical Pacific Heat Recharge

NASA Astrophysics Data System (ADS)

Mayer, Michael; Alonso Balmaseda, Magdalena; Haimberger, Leopold

2018-04-01

El Niño events are characterized by anomalously warm tropical Pacific surface waters and concurrent ocean heat discharge, a precursor of subsequent cold La Niña conditions. Here we show that El Niño 2015/2016 departed from this norm: despite extreme peak surface temperatures, tropical Pacific (30°N-30°S) upper ocean heat content increased by 9.6 ± 1.7 ZJ (1 ZJ = 1021 J), in stark contrast to the previous strong El Niño in 1997/1998 (-11.5 ± 2.9 ZJ). Unprecedented reduction of Indonesian Throughflow volume and heat transport played a key role in the anomalous 2015/2016 event. We argue that this anomaly is linked with the previously documented intensified warming and associated rising sea levels in the Indian Ocean during the last decade. Additionally, increased absorption of solar radiation acted to dampen Pacific ocean heat content discharge. These results explain the weak and short-lived La Niña conditions in 2016/2017 and indicate the need for realistic representation of Indo-Pacific energy transfers for skillful seasonal-to-decadal predictions.

Mitigation benefits of forestation greatly varies on short spatial scale

NASA Astrophysics Data System (ADS)

Yakir, Dan; Rotenberg, Eyal; Rohatin, Shani; Ramati, Efrat; Asaf, David; Dicken, Uri

2016-04-01

Mitigation of global warming by forestation is controversial because of its linkage to increasing surface energy load and associated surface warming. Such tradeoffs between cooling associated with carbon sequestration and warming associated with radiative effects have been considered predominantly on large spatial scales, indicating benefits of forestation mainly in the tropics but not in the boreal regions. Using mobile laboratory for measuring CO2, water and energy flux in forest and non-forest ecosystem along the climatic gradient in Israel over three years, we show that the balance between cooling and warming effects of forestation can be transformed across small spatial scale. While converting shrubland to pine forest in a semi-arid site (280 mm annual precipitations) requires several decades of carbon sequestration to balance the radiative warming effects, similar land use change under moist Mediterranean conditions (780 mm annual precipitation) just ~200 km away showed reversal of this balance. Specifically, the results indicated that in the study region (semi-arid to humid Mediterranean), net absorb radiation in pine forests is always larger than in open space ecosystems, resulting in surface warming effects (the so-called albedo effect). Similarly, depression of thermal radiation emission, mainly due canopy skin surface cooling associated with the 'convector effect' in forests compared with shrubland ecosystems also appears in all sites. But both effects decrease by about 1/2 in going from the semi-arid to the humid Mediterranean sites, while enhanced productivity of forest compared to grassland increase about fourfold. The results indicate a greater potential for forestation as climate change mitigation strategy than previously assumed.

Physical Mechanisms of Rapid Lake Warming

NASA Astrophysics Data System (ADS)

Lenters, J. D.

2016-12-01

Recent studies have shown significant warming of inland water bodies around the world. Many lakes are warming more rapidly than the ambient surface air temperature, and this is counter to what is often expected based on the lake surface energy balance. A host of reasons have been proposed to explain these discrepancies, including changes in the onset of summer stratification, significant loss of ice cover, and concomitant changes in winter air temperature and/or summer cloud cover. A review of the literature suggests that no single physical mechanism is primarily responsible for the majority of these changes, but rather that the large heterogeneity in regional climate trends and lake geomorphometry results in a host of potential physical drivers. In this study, we discuss the variety of mechanisms that have been proposed to explain rapid lake warming and offer an assessment of the physical plausibility for each potential contributor. Lake Superior is presented as a case study to illustrate the "perfect storm" of factors that can cause a deep, dimictic lake to warm at rate that exceeds the rate of global air temperature warming by nearly an order of magnitude. In particular, we use a simple mixed-layer model to show that spatially variable trends in Lake Superior surface water temperature are determined, to first order, by variations in bathymetry and winter air temperature. Summer atmospheric conditions are often of less significance, and winter ice cover may simply be a correlate. The results highlight the importance of considering the full range of factors that can lead to trends in lake surface temperature, and that conventional wisdom may often not be the best guide.

The influence of global sea surface temperature variability on the large-scale land surface temperature

NASA Astrophysics Data System (ADS)

Tyrrell, Nicholas L.; Dommenget, Dietmar; Frauen, Claudia; Wales, Scott; Rezny, Mike

2015-04-01

In global warming scenarios, global land surface temperatures () warm with greater amplitude than sea surface temperatures (SSTs), leading to a land/sea warming contrast even in equilibrium. Similarly, the interannual variability of is larger than the covariant interannual SST variability, leading to a land/sea contrast in natural variability. This work investigates the land/sea contrast in natural variability based on global observations, coupled general circulation model simulations and idealised atmospheric general circulation model simulations with different SST forcings. The land/sea temperature contrast in interannual variability is found to exist in observations and models to a varying extent in global, tropical and extra-tropical bands. There is agreement between models and observations in the tropics but not the extra-tropics. Causality in the land-sea relationship is explored with modelling experiments forced with prescribed SSTs, where an amplification of the imposed SST variability is seen over land. The amplification of to tropical SST anomalies is due to the enhanced upper level atmospheric warming that corresponds with tropical moist convection over oceans leading to upper level temperature variations that are larger in amplitude than the source SST anomalies. This mechanism is similar to that proposed for explaining the equilibrium global warming land/sea warming contrast. The link of the to the dominant mode of tropical and global interannual climate variability, the El Niño Southern Oscillation (ENSO), is found to be an indirect and delayed connection. ENSO SST variability affects the oceans outside the tropical Pacific, which in turn leads to a further, amplified and delayed response of.

Recent Warming of Lake Kivu

PubMed Central

Katsev, Sergei; Aaberg, Arthur A.; Crowe, Sean A.; Hecky, Robert E.

2014-01-01

Lake Kivu in East Africa has gained notoriety for its prodigious amounts of dissolved methane and dangers of limnic eruption. Being meromictic, it is also expected to accumulate heat due to rising regional air temperatures. To investigate the warming trend and distinguish between atmospheric and geothermal heating sources, we compiled historical temperature data, performed measurements with logging instruments, and simulated heat propagation. We also performed isotopic analyses of water from the lake's main basin and isolated Kabuno Bay. The results reveal that the lake surface is warming at the rate of 0.12°C per decade, which matches the warming rates in other East African lakes. Temperatures increase throughout the entire water column. Though warming is strongest near the surface, warming rates in the deep waters cannot be accounted for solely by propagation of atmospheric heat at presently assumed rates of vertical mixing. Unless the transport rates are significantly higher than presently believed, this indicates significant contributions from subterranean heat sources. Temperature time series in the deep monimolimnion suggest evidence of convection. The progressive deepening of the depth of temperature minimum in the water column is expected to accelerate the warming in deeper waters. The warming trend, however, is unlikely to strongly affect the physical stability of the lake, which depends primarily on salinity gradient. PMID:25295730

Recent warming of lake Kivu.

PubMed

Katsev, Sergei; Aaberg, Arthur A; Crowe, Sean A; Hecky, Robert E

2014-01-01

Lake Kivu in East Africa has gained notoriety for its prodigious amounts of dissolved methane and dangers of limnic eruption. Being meromictic, it is also expected to accumulate heat due to rising regional air temperatures. To investigate the warming trend and distinguish between atmospheric and geothermal heating sources, we compiled historical temperature data, performed measurements with logging instruments, and simulated heat propagation. We also performed isotopic analyses of water from the lake's main basin and isolated Kabuno Bay. The results reveal that the lake surface is warming at the rate of 0.12°C per decade, which matches the warming rates in other East African lakes. Temperatures increase throughout the entire water column. Though warming is strongest near the surface, warming rates in the deep waters cannot be accounted for solely by propagation of atmospheric heat at presently assumed rates of vertical mixing. Unless the transport rates are significantly higher than presently believed, this indicates significant contributions from subterranean heat sources. Temperature time series in the deep monimolimnion suggest evidence of convection. The progressive deepening of the depth of temperature minimum in the water column is expected to accelerate the warming in deeper waters. The warming trend, however, is unlikely to strongly affect the physical stability of the lake, which depends primarily on salinity gradient.

Eemian interglacial reconstructed from a Greenland folded ice core.

PubMed

2013-01-24

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Characteristics of early winter high Arctic atmospheric boundary layer profiles

NASA Astrophysics Data System (ADS)

Wickström, Siiri; Vihma, Timo; Nygård, Tiina; Kramer, Daniel; Palo, Timo; Jonassen, Marius

2017-04-01

For a large part of the year, the Arctic climate system is characterised by a stably stratified atmospheric boundary layer, with strong temperature inversions isolating the surface from the air aloft. These nversions are typically driven by longwave radiative cooling, warm-air advection aloft, or subsidence. All these mechanisms are affected by the synoptic sate of the atmosphere in the high Arctic. In this study we present data from an intensive measurement campaign in Svalbard in October 2014, when atmospheric profiles were measured with a tethered balloon in Adventdalen and Hornsund. In addition radiosonde soundings from Ny-Ålesund were analysed. A total of 115 individual profiles were analysed, almost all of them showing a surface-based temperature inversion. Our preliminary results show that the strongest and deepest inversions are observed at the beginning of a warm-air advection event, but as the temperature, wind and cloudiness increase the inversion strength and depth decrease rapidly. The inversion curvature parameter seems to be strongly dependent on the longwave radiative balance with the highest curvatures (strongest vertical temperature gradient close to the surface) associated with strong longwave radiative heat loss from the surface. The different processes affecting the stable atmospheric boundary layer during a low-pressure passage are determined, and the effects of the synoptic scale changes are isolated from those caused by local topographic forcing.

Measurements of solar and terrestrial heating and cooling rate profiles in Arctic and sub-tropic stratocumulus

NASA Astrophysics Data System (ADS)

Gottschalk, Matthias; Lauermann, Felix; Ehrlich, André; Siebert, Holger; Wendisch, Manfred

2017-04-01

Stratocumulus covers approximately 20 % (annually averaged) of the Earth's surface and thus strongly influences the atmospheric and surface radiative energy budget resulting in radiative cooling and heating effects. Globally, the solar cooling effect of the widespread sub-tropical stratocumulus dominates. However, in the Arctic the solar cloud albedo effect (cooling) is often smaller than the thermal-infrared greenhouse effect (warming), which is a result of the lower incoming solar radiation and the low cloud base height. Therefore, Arctic stratocumulus mostly warms the atmosphere and surface below the cloud. Additionally, different environmental conditions lead to differences between sub-tropical and Arctic stratocumulus. Broadband pyranometers and pyrgeometers will be used to measure heating and cooling rate profiles in and above stratocumulus. For this purpose two slowly moving platforms are used (helicopter and tethered balloon) in order to consider for the long response times of both broadband radiation sensors. Two new instrument packages are developed for the applied tethered balloon and helicopter platforms, which will be operated within Arctic and sub-tropical stratocumulus, respectively. In June 2017, the balloon will be launched from a sea ice floe north of 80 °N during the Arctic Balloon-borne profiling Experiment (ABEX) as part of (AC)3 (Arctic Amplification: Climate Relevant Atmospheric and Surface Processes and Feedback Mechanisms) Transregional Collaborative Research Center. The helicopter will sample sub-tropical stratocumulus over the Azores in July 2017.

On the direct impact of the CO2 concentration rise to the global warming

NASA Astrophysics Data System (ADS)

Laubereau, Alfred; Iglev, Hristo

2013-10-01

The growing amount of carbon dioxide in the atmosphere is often considered as the dominant factor for the global warming during the past decades. The noted correlation, however, does not answer the question about causality. In addition, the reported temperature data do not display a simple relationship between the monotonic concentration increase from 1880 to 2010 and the non-monotonic temperature rise during the same period. We have performed new measurements for optically thick samples of CO2 and investigate its role for the greenhouse effect on the basis of these spectroscopic data. Using simplified global models the warming of the surface is computed and a relatively modest effect is found, only: from the reported CO2 concentration rise in the atmosphere from 290 to 385 ppmv in 1880 to 2010 we derive a direct temperature rise of 0.26+/-0.01\\ \\text{K} . Including the simultaneous feedback effect of atmospheric water we still arrive at a minor CO2 contribution of less than 33% to the reported global warming of {\\sim}1.2\\ \\text{K} . It is suggested that other factors that are known to influence the greenhouse effect, e.g. air pollution by black carbon should be considered in more detail to fully understand the global temperature change.

Emerging Vibrio risk at high latitudes in response to ocean warming

NASA Astrophysics Data System (ADS)

Baker-Austin, Craig; Trinanes, Joaquin A.; Taylor, Nick G. H.; Hartnell, Rachel; Siitonen, Anja; Martinez-Urtaza, Jaime

2013-01-01

There is increasing concern regarding the role of climate change in driving bacterial waterborne infectious diseases. Here we illustrate associations between environmental changes observed in the Baltic area and the recent emergence of Vibrio infections and also forecast future scenarios of the risk of infections in correspondence with predicted warming trends. Using multidecadal long-term sea surface temperature data sets we found that the Baltic Sea is warming at an unprecedented rate. Sea surface temperature trends (1982-2010) indicate a warming pattern of 0.063-0.078°Cyr-1 (6.3-7.8°C per century; refs , ), with recent peak temperatures unequalled in the history of instrumented measurements for this region. These warming patterns have coincided with the unexpected emergence of Vibrio infections in northern Europe, many clustered around the Baltic Sea area. The number and distribution of cases correspond closely with the temporal and spatial peaks in sea surface temperatures. This is among the first empirical evidence that anthropogenic climate change is driving the emergence of Vibrio disease in temperate regions through its impact on resident bacterial communities, implying that this process is reshaping the distribution of infectious diseases across global scales.

Regional patterns of the change in annual-mean tropical rainfall under global warming

NASA Astrophysics Data System (ADS)

Huang, P.

2013-12-01

Projection of the change in tropical rainfall under global warming is a major challenge with great societal implications. The current study analyzes the 18 models from the Coupled Models Intercomparison Project, and investigates the regional pattern of annual-mean rainfall change under global warming. With surface warming, the climatological ascending pumps up increased surface moisture and leads rainfall increase over the tropical convergence zone (wet-get-wetter effect), while the pattern of sea surface temperature (SST) increase induces ascending flow and then increasing rainfall over the equatorial Pacific and the northern Indian Ocean where the local oceanic warming exceeds the tropical mean temperature increase (warmer-get-wetter effect). The background surface moisture and SST also can modify warmer-get-wetter effect: the former can influence the moisture change and contribute to the distribution of moist instability change, while the latter can suppress the role of instability change over the equatorial eastern Pacific due to the threshold effect of convection-SST relationship. The wet-get-wetter and modified warmer-get-wetter effects form a hook-like pattern of rainfall change over the tropical Pacific and an elliptic pattern over the northern Indian Ocean. The annual-mean rainfall pattern can be partly projected based on current rainfall climatology, while it also has great uncertainties due to the uncertain change in SST pattern.

Could cirrus clouds have warmed early Mars?

NASA Astrophysics Data System (ADS)

Ramirez, Ramses M.; Kasting, James F.

2017-01-01

The presence of the ancient valley networks on Mars indicates that the climate at 3.8 Ga was warm enough to allow substantial liquid water to flow on the martian surface for extended periods of time. However, the mechanism for producing this warming continues to be debated. One hypothesis is that Mars could have been kept warm by global cirrus cloud decks in a CO2sbnd H2O atmosphere containing at least 0.25 bar of CO2 (Urata and Toon, 2013). Initial warming from some other process, e.g., impacts, would be required to make this model work. Those results were generated using the CAM 3-D global climate model. Here, we use a single-column radioactive-convective climate model to further investigate the cirrus cloud warming hypothesis. Our calculations indicate that cirrus cloud decks could have produced global mean surface temperatures above freezing, but only if cirrus cloud cover approaches ∼75 - 100% and if other cloud properties (e.g., height, optical depth, particle size) are chosen favorably. However, at more realistic cirrus cloud fractions, or if cloud parameters are not optimal, cirrus clouds do not provide the necessary warming, suggesting that other greenhouse mechanisms are needed.

Global lake response to the recent warming hiatus

NASA Astrophysics Data System (ADS)

Winslow, Luke A.; Leach, Taylor H.; Rose, Kevin C.

2018-05-01

Understanding temporal variability in lake warming rates over decadal scales is important for understanding observed change in aquatic systems. We analyzed a global dataset of lake surface water temperature observations (1985‑2009) to examine how lake temperatures responded to a recent global air temperature warming hiatus (1998‑2012). Prior to the hiatus (1985‑1998), surface water temperatures significantly increased at an average rate of 0.532 °C decade‑1 (±0.214). In contrast, water temperatures did not change significantly during the hiatus (average rate ‑0.087 °C decade‑1 ±0.223). Overall, 83% of lakes in our dataset (129 of 155) had faster warming rates during the pre-hiatus period than during the hiatus period. These results demonstrate that lakes have exhibited decadal-scale variability in warming rates coherent with global air temperatures and represent an independent line of evidence for the recent warming hiatus. Our analyses provide evidence that lakes are sentinels of broader climatological processes and indicate that warming rates based on datasets where a large proportion of observations were collected during the hiatus period may underestimate longer-term trends.

Regional warming of hot extremes accelerated by surface energy fluxes consistent with drying soils

NASA Astrophysics Data System (ADS)

Donat, M.; Pitman, A.; Seneviratne, S. I.

2017-12-01

Strong regional differences exist in how hot temperature extremes increase under global warming. Using an ensemble of coupled climate models, we examine the regional warming rates of hot extremes relative to annual average warming rates in the same regions. We identify hotspots of accelerated warming of model-simulated hot extremes in Europe, North America, South America and Southeast China. These hotspots indicate where the warm tail of a distribution of temperatures increases faster than the average and are robust across most CMIP5 models. Exploring the conditions on the specific day the hot extreme occurs demonstrates the hotspots are explained by changes in the surface energy fluxes consistent with drying soils. Furthermore, in these hotspot regions we find a relationship between the temperature - heat flux correlation under current climate conditions and the magnitude of future projected changes in hot extremes, pointing to a potential emergent constraint for simulations of future hot extremes. However, the model-simulated accelerated warming of hot extremes appears inconsistent with observations of the past 60 years, except over Europe. The simulated acceleration of hot extremes may therefore be unreliable, a result that necessitates a re-evaluation of how climate models resolve the relevant terrestrial processes.

A High-Latitude Winter Continental Low Cloud Feedback Suppresses Arctic Air Formation in Warmer Climates

NASA Astrophysics Data System (ADS)

Cronin, T.; Tziperman, E.; Li, H.

2015-12-01

High latitude continents have warmed much more rapidly in recent decades than the rest of the globe, especially in winter, and the maintenance of warm, frost-free conditions in continental interiors in winter has been a long-standing problem of past equable climates. It has also been found that the high-latitude lapse rate feedback plays an important role in Arctic amplification of climate change in climate model simulations, but we have little understanding of why lapse rates at high latitudes change so strongly with warming. To better understand these problems, we study Arctic air formation - the process by which a high-latitude maritime air mass is advected over a continent during polar night, cooled at the surface by radiation, and transformed into a much colder continental polar air mass - and its sensitivity to climate warming. We use a single-column version of the WRF model to conduct two-week simulations of the cooling process across a wide range of initial temperature profiles and microphysics schemes, and find that a low cloud feedback suppresses Arctic air formation in warmer climates. This cloud feedback consists of an increase in low cloud amount with warming, which shields the surface from radiative cooling, and increases the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature. The time it takes for the surface air temperature to drop below freezing increases nonlinearly to ~10 days for initial maritime surface air temperatures of 20 oC. Given that this is about the time it takes an air mass starting over the Pacific to traverse the north American continent, this suggests that optically thick stratus cloud decks could help to maintain frost-free winter continental interiors in equable climates. We find that CMIP5 climate model runs show large increases in cloud water path and surface cloud longwave forcing in warmer climates, consistent with the proposed low-cloud feedback. The suppression of Arctic air formation with warming may act as a significant amplifier of climate change at high latitudes, and offers a mechanistic perspective on the high-latitude "lapse rate feedback" diagnosed in climate models.

Contrasting Effects of Central Pacific and Eastern Pacific El Nino on Stratospheric Water Vapor

NASA Technical Reports Server (NTRS)

Garfinkel, Chaim I.; Hurwitz, Margaret M.; Oman, Luke D.; Waugh, Darryn W.

2013-01-01

Targeted experiments with a comprehensive chemistry-climate model are used to demonstrate that seasonality and the location of the peak warming of sea surface temperatures dictate the response of stratospheric water vapor to El Nino. In spring, El Nino events in which sea surface temperature anomalies peak in the eastern Pacific lead to a warming at the tropopause above the warm pool region, and subsequently to more stratospheric water vapor (consistent with previous work). However, in fall and in early winter, and also during El Nino events in which the sea surface temperature anomaly is found mainly in the central Pacific, the response is qualitatively different: temperature changes in the warm pool region are nonuniform and less water vapor enters the stratosphere. The difference in water vapor in the lower stratosphere between the two variants of El Nino approaches 0.3 ppmv, while the difference between the winter and spring responses exceeds 0.5 ppmv.

Transient regional climate change: analysis of the summer climate response in a high-resolution, century-scale, ensemble experiment over the continental United States

PubMed Central

Diffenbaugh, Noah S.; Ashfaq, Moetasim; Scherer, Martin

2013-01-01

Integrating the potential for climate change impacts into policy and planning decisions requires quantification of the emergence of sub-regional climate changes that could occur in response to transient changes in global radiative forcing. Here we report results from a high-resolution, century-scale, ensemble simulation of climate in the United States, forced by atmospheric constituent concentrations from the Special Report on Emissions Scenarios (SRES) A1B scenario. We find that 21st century summer warming permanently emerges beyond the baseline decadal-scale variability prior to 2020 over most areas of the continental U.S. Permanent emergence beyond the baseline annual-scale variability shows much greater spatial heterogeneity, with emergence occurring prior to 2030 over areas of the southwestern U.S., but not prior to the end of the 21st century over much of the southcentral and southeastern U.S. The pattern of emergence of robust summer warming contrasts with the pattern of summer warming magnitude, which is greatest over the central U.S. and smallest over the western U.S. In addition to stronger warming, the central U.S. also exhibits stronger coupling of changes in surface air temperature, precipitation, and moisture and energy fluxes, along with changes in atmospheric circulation towards increased anticylonic anomalies in the mid-troposphere and a poleward shift in the mid-latitude jet aloft. However, as a fraction of the baseline variability, the transient warming over the central U.S. is smaller than the warming over the southwestern or northeastern U.S., delaying the emergence of the warming signal over the central U.S. Our comparisons with observations and the Coupled Model Intercomparison Project Phase 3 (CMIP3) ensemble of global climate model experiments suggest that near-term global warming is likely to cause robust sub-regional-scale warming over areas that exhibit relatively little baseline variability. In contrast, where there is greater variability in the baseline climate dynamics, there can be greater variability in the response to elevated greenhouse forcing, decreasing the robustness of the transient warming signal. PMID:24307747

Ten years of measurements and modeling of soil temperature changes and their effects on permafrost in Northwestern Alaska

NASA Astrophysics Data System (ADS)

Batir, Joseph F.; Hornbach, Matthew J.; Blackwell, David D.

2017-01-01

Multiple studies demonstrate Northwest Alaska and the Alaskan North Slope are warming. Melting permafrost causes surface destabilization and ecological changes. Here, we use thermistors permanently installed in 1996 in a borehole in northwestern Alaska to study past, present, and future ground and subsurface temperature change, and from this, forecast future permafrost degradation in the region. We measure and model Ground Surface Temperature (GST) warming trends for a 10 year period using equilibrium Temperature-Depth (TD) measurements from borehole T96-012, located near the Red Dog Mine in northwestern Alaska-part of the Arctic ecosystem where a continuous permafrost layer exists. Temperature measurements from 1996 to 2006 indicate the subsurface has clearly warmed at depths shallower than 70 m. Seasonal climate effects are visible in the data to a depth of 30 m based on a visible sinusoidal pattern in the TD plots that correlate with season patterns. Using numerical models constrained by thermal conductivity and temperature measurements at the site, we show that steady warming at depths of 30 to 70 m is most likely the direct result of longer term (decadal-scale) surface warming. The analysis indicates the GST in the region is warming at 0.44 ± 0.05 °C/decade, a value consistent with Surface Air Temperature (SAT) warming of 1.0 ± 0.8 °C/decade observed at Red Dog Mine, but with much lower uncertainty. The high annual variability in the SAT signal produces significant uncertainty in SAT trends. The high annual variability is filtered out of the GST signal by the low thermal diffusivity of the subsurface. Comparison of our results to recent permafrost monitoring studies suggests changes in latitude in the polar regions significantly impacts warming rates. North Slope average GST warming is 0.9 ± 0.5 °C/decade, double our observations at RDM, but within error. The RDM warming rate is within the warming variation observed in eastern Alaska, 0.36-0.71 °C/decade, which suggests changes in longitude produce a smaller impact but have warming variability likely related to ecosystem, elevation, microclimates, etc. changes. We also forward model future warming by assuming a 1D diffusive heat flow model and incorporating latent heat effects for permafrost melting. Our analysis indicates 1 to 4 m of loss at the upper permafrost boundary, a 145 ± 100% increase in the active layer thickness by 2055. If warming continues at a constant rate of 0.44 ± 0.05 °C/decade, we estimate the 125 m thick zone of permafrost at this site will completely melt by 2150. Permafrost is expected to melt by 2200, 2110, or 2080, if the rate of warming is altered to 0.25, 0.90, or 2.0 °C/decade, respectively, as an array of different climate models suggest. Since our model assumes no advection of heat (a more efficient heat transport mechanism), and no accelerated warming, our current prediction of complete permafrost loss by 2150 may overestimate the residence time of permafrost in this region of Northwest Alaska.

Shifts in the Physiology and Stoichiometric Needs of Soil Microbial Communities from Subarctic Soils in Response to Warming: Icelandic Geothermal Gradients as a Model.

NASA Astrophysics Data System (ADS)

Marañón-Jiménez, S.; Soong, J.; Leblans, N. I. W.; Sigurdsson, B. D.; Peñuelas, J.; Richter, A.; Asensio, D.; Fransen, E.; Janssens, I. A.

2017-12-01

Large amounts of CO2 can be released to the atmosphere from a faster mineralization of soil organic matter at warmer temperatures, thus inducing climate change feedbacks. Specifically, soils at high northern latitudes store more than half of the global surface soil carbon and are particularly vulnerable to temperature-driven C losses, since they warm more rapidly. Alterations to the temperature sensitivity, physiological functioning and stoichiometric constrains of soil microorganisms in response to rising temperatures can play a key role in these soil carbon (C) losses. We present results of several incubation experiments using soils from geothermal soil temperature gradients in Iceland that have undergone a range of warming intensities for seven years, encompassing the full range of IPCC warming scenarios for the northern region. Soil microbes from warmed soils did not show changes in their temperature sensitivity at the physiological level. On the contrary, seven years of chronic soil warming provoked a permanent increase of microbial metabolic quotients (i.e., respiration per unit of biomass), and a subsequent reduction in the C retained in biomass as substrate became limiting. After the initial depletion of labile soil C, increasing energy demands for metabolic maintenance and resource acquisition at higher temperatures may have triggered permanent functional changes or community shifts towards increasing respiratory costs of soil decomposers. Pointing to this, microbial communities showed a strong C limitation even at ambient soil temperatures, obscuring any metabolic response to nitrogen and phosphorous additions. The tight C:N stoichiometric constrains of soil microbial communities and the strong C limitation for microbial biomass may lead to a reduced capacity of microbial N retention, explaining the equivalent soil C and N losses found in response to soil warming. These results highlight the need to incorporate potential changes in microbial physiological functioning and stoichiometric needs into models, in order to accurately predict future changes in soil C stocks in response to global warming.

Holocene thermal maximum in the western Arctic (0-180°W)

USGS Publications Warehouse

Kaufman, D.S.; Ager, T.A.; Anderson, N.J.; Anderson, P.M.; Andrews, John T.; Bartlein, P.J.; Brubaker, L.B.; Coats, Larry L.; Cwynar, L.C.; Duvall, M.L.; Dyke, A.S.; Edwards, M.E.; Eisner, Wendy R.; Gajewski, K.; Geirsdottir, A.; Hu, F.-S.; Jennings, A.E.; Kaplan, M.R.; Kerwin, M.W.; Lozhkin, A.V.; MacDonald, G.M.; Miller, G.H.; Mock, Cary J.; Oswald, W.W.; Otto-Bliesner, B. L.; Porinchu, David F.; Ruhland, K.; Smol, J.P.; Steig, E.J.; Wolfe, B.B.

2004-01-01

The spatio-temporal pattern of peak Holocene warmth (Holocene thermal maximum, HTM) is traced over 140 sites across the Western Hemisphere of the Arctic (0-180??W; north of ???60??N). Paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer-than-present conditions at 120 of these sites. At the 16 terrestrial sites where quantitative estimates have been obtained, local HTM temperatures (primarily summer estimates) were on average 1.6??0.8??C higher than present (approximate average of the 20th century), but the warming was time-transgressive across the western Arctic. As the precession-driven summer insolation anomaly peaked 12-10ka (thousands of calendar years ago), warming was concentrated in northwest North America, while cool conditions lingered in the northeast. Alaska and northwest Canada experienced the HTM between ca 11 and 9ka, about 4000yr prior to the HTM in northeast Canada. The delayed warming in Quebec and Labrador was linked to the residual Laurentide Ice Sheet, which chilled the region through its impact on surface energy balance and ocean circulation. The lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change. The spatial asymmetry of warming during the HTM resembles the pattern of warming observed in the Arctic over the last several decades. Although the two warmings are described at different temporal scales, and the HTM was additionally affected by the residual Laurentide ice, the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing. Unlike the HTM, however, future warming will not be counterbalanced by the cooling effect of a residual North American ice sheet. ?? 2003 Elsevier Ltd. All rights reserved.

Holocene thermal maximum in the western Arctic (0-180°W)

NASA Astrophysics Data System (ADS)

Kaufman, D. S.; Ager, T. A.; Anderson, N. J.; Anderson, P. M.; Andrews, J. T.; Bartlein, P. J.; Brubaker, L. B.; Coats, L. L.; Cwynar, L. C.; Duvall, M. L.; Dyke, A. S.; Edwards, M. E.; Eisner, W. R.; Gajewski, K.; Geirsdóttir, A.; Hu, F. S.; Jennings, A. E.; Kaplan, M. R.; Kerwin, M. W.; Lozhkin, A. V.; MacDonald, G. M.; Miller, G. H.; Mock, C. J.; Oswald, W. W.; Otto-Bliesner, B. L.; Porinchu, D. F.; Rühland, K.; Smol, J. P.; Steig, E. J.; Wolfe, B. B.

2004-03-01

The spatio-temporal pattern of peak Holocene warmth (Holocene thermal maximum, HTM) is traced over 140 sites across the Western Hemisphere of the Arctic (0-180°W; north of ˜60°N). Paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer-than-present conditions at 120 of these sites. At the 16 terrestrial sites where quantitative estimates have been obtained, local HTM temperatures (primarily summer estimates) were on average 1.6±0.8°C higher than present (approximate average of the 20th century), but the warming was time-transgressive across the western Arctic. As the precession-driven summer insolation anomaly peaked 12-10 ka (thousands of calendar years ago), warming was concentrated in northwest North America, while cool conditions lingered in the northeast. Alaska and northwest Canada experienced the HTM between ca 11 and 9 ka, about 4000 yr prior to the HTM in northeast Canada. The delayed warming in Quebec and Labrador was linked to the residual Laurentide Ice Sheet, which chilled the region through its impact on surface energy balance and ocean circulation. The lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change. The spatial asymmetry of warming during the HTM resembles the pattern of warming observed in the Arctic over the last several decades. Although the two warmings are described at different temporal scales, and the HTM was additionally affected by the residual Laurentide ice, the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing. Unlike the HTM, however, future warming will not be counterbalanced by the cooling effect of a residual North American ice sheet.

Solar Radiation and Cloud Radiative Forcing in the Pacific Warm Pool Estimated Using TOGA COARE Measurements

NASA Technical Reports Server (NTRS)

Chou, Ming-Dah; Chou, Shu-Hsien; Zhao, Wenzhong

1999-01-01

The energy budget of the tropical western Pacific (TWP) is particularly important because this is one of the most energetic convection regions on the Earth. Nearly half of the solar radiation incident at the top of atmosphere is absorbed at the surface and only about 22% absorbed in the atmosphere. A large portion of the excess heat absorbed at the surface is transferred to the atmosphere through evaporation, which provides energy and water for convection and precipitation. The western equatorial Pacific is characterized by the highest sea surface temperature (SST) and heaviest rainfall in the world ocean. A small variation of SST associated with the eastward shift of the warm pool during El-Nino/Souther Oscillation changes the atmospheric circulation pattern and affects the global climate. In a study of the TWP surface heat and momentum fluxes during the Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) Intensive observing period (IOP) from November 1992 to February have found that the solar radiation is the most important component of the surface energy budget, which undergoes significant temporal and spatial variation. The variations are influenced by the two 40-50 days Madden Julian Oscillations (MJOs) which propagated eastward from the Indian Ocean to the Central Pacific during the IOP. The TWP surface solar radiation during the COARE IOP was investigated by a number of studies. In addition, the effects of clouds on the solar heating of the atmosphere in the TWP was studied using energy budget analysis. In this study, we present some results of the TWP surface solar shortwave or SW radiation budget and the effect of clouds on the atmospheric solar heating using the surface radiation measurements and Japan's Geostationary Meteorological Satellite 4 radiance measurements during COARE IOP.

Heating and Cooling Rates With an Esophageal Heat Exchange System.

PubMed

Kalasbail, Prathima; Makarova, Natalya; Garrett, Frank; Sessler, Daniel I

2018-04-01

The Esophageal Cooling Device circulates warm or cool water through an esophageal heat exchanger, but warming and cooling efficacy in patients remains unknown. We therefore determined heat exchange rates during warming and cooling. Nineteen patients completed the trial. All had general endotracheal anesthesia for nonthoracic surgery. Intraoperative heat transfer was measured during cooling (exchanger fluid at 7°C) and warming (fluid at 42°C). Each was evaluated for 30 minutes, with the initial condition determined randomly, starting at least 40 minutes after induction of anesthesia. Heat transfer rate was estimated from fluid flow through the esophageal heat exchanger and inflow and outflow temperatures. Core temperature was estimated from a zero-heat-flux thermometer positioned on the forehead. Mean heat transfer rate during warming was 18 (95% confidence interval, 16-20) W, which increased core temperature at a rate of 0.5°C/h ± 0.6°C/h (mean ± standard deviation). During cooling, mean heat transfer rate was -53 (-59 to -48) W, which decreased core temperature at a rate of 0.9°C/h ± 0.9°C/h. Esophageal warming transferred 18 W which is considerably less than the 80 W reported with lower or upper body forced-air covers. However, esophageal warming can be used to supplement surface warming or provide warming in cases not amenable to surface warming. Esophageal cooling transferred more than twice as much heat as warming, consequent to the much larger difference between core and circulating fluid temperature with cooling (29°C) than warming (6°C). Esophageal cooling extracts less heat than endovascular catheters but can be used to supplement catheter-based cooling or possibly replace them in appropriate patients.

The whole-soil carbon flux in response to warming

NASA Astrophysics Data System (ADS)

Hicks Pries, Caitlin E.; Castanha, C.; Porras, R. C.; Torn, M. S.

2017-03-01

Soil organic carbon harbors three times as much carbon as Earth’s atmosphere, and its decomposition is a potentially large climate change feedback and major source of uncertainty in climate projections. The response of whole-soil profiles to warming has not been tested in situ. In a deep warming experiment in mineral soil, we found that CO2 production from all soil depths increased with 4°C warming; annual soil respiration increased by 34 to 37%. All depths responded to warming with similar temperature sensitivities, driven by decomposition of decadal-aged carbon. Whole-soil warming reveals a larger soil respiration response than many in situ experiments (most of which only warm the surface soil) and models.

Quantification of Local Warming Trend: A Remote Sensing-Based Approach

PubMed Central

Rahaman, Khan Rubayet; Hassan, Quazi K.

2017-01-01

Understanding the warming trends at local level is critical; and, the development of relevant adaptation and mitigation policies at those levels are quite challenging. Here, our overall goal was to generate local warming trend map at 1 km spatial resolution by using: (i) Moderate Resolution Imaging Spectroradiometer (MODIS)-based 8-day composite surface temperature data; (ii) weather station-based yearly average air temperature data; and (iii) air temperature normal (i.e., 30 year average) data over the Canadian province of Alberta during the period 1961–2010. Thus, we analysed the station-based air temperature data in generating relationships between air temperature normal and yearly average air temperature in order to facilitate the selection of year-specific MODIS-based surface temperature data. These MODIS data in conjunction with weather station-based air temperature normal data were then used to model local warming trends. We observed that almost 88% areas of the province experienced warming trends (i.e., up to 1.5°C). The study concluded that remote sensing technology could be useful for delineating generic trends associated with local warming. PMID:28072857

Longitudinal Changes in Tear Evaporation Rates After Eyelid Warming Therapies in Meibomian Gland Dysfunction.

PubMed

Yeo, Sharon; Tan, Jen Hong; Acharya, U Rajendra; Sudarshan, Vidya K; Tong, Louis

2016-04-01

Lid warming is the major treatment for meibomian gland dysfunction (MGD). The purpose of the study was to determine the longitudinal changes of tear evaporation after lid warming in patients with MGD. Ninety patients with MGD were enrolled from a dry eye clinic at Singapore National Eye Center in an interventional trial. Participants were treated with hot towel (n = 22), EyeGiene (n = 22), or Blephasteam (n = 22) twice daily or a single 12-minute session of Lipiflow (n = 24). Ocular surface infrared thermography was performed at baseline and 4 and 12 weeks after the treatment, and image features were extracted from the captured images. The baseline of conjunctival tear evaporation (TE) rate (n = 90) was 66.1 ± 21.1 W/min. The rates were not significantly different between sexes, ages, symptom severities, tear breakup times, Schirmer test, corneal fluorescein staining, or treatment groups. Using a general linear model (repeat measures), the conjunctival TE rate was reduced with time after treatment. A higher baseline evaporation rate (≥ 66 W/min) was associated with greater reduction of evaporation rate after treatment. Seven of 10 thermography features at baseline were predictive of reduction in irritative symptoms after treatment. Conjunctival TE rates can be effectively reduced by lid warming treatment in some MGD patients. Individual baseline thermography image features can be predictive of the response to lid warming therapy. For patients that do not have excessive TE, additional therapy, for example, anti-inflammatory therapy, may be required.

Alkali metal pool boiler life tests for a 25 kWe advanced Stirling conversion system

NASA Technical Reports Server (NTRS)

Anderson, W. G.; Rosenfeld, J. H.; Noble, J.

1991-01-01

The overall operating temperature and efficiency of solar-powered Stirling engines can be improved by adding an alkali metal pool boiler heat transport system to supply heat more uniformly to the heater head tubes. One issue with liquid metal pool boilers is unstable boiling. Stable boiling is obtained with an enhanced boiling surface containing nucleation sites that promote continuous boiling. Over longer time periods, it is possible that the boiling behavior of the system will change. An 800-h life test was conducted to verify that pool boiling with the chosen fluid/surface combination remains stable as the system ages. The apparatus uses NaK boiling on a - 100 + 140 stainless steel sintered porous layer, with the addition of a small amount of xenon. Pool boiling remained stable to the end of life test. The pool boiler life test included a total of 82 cold starts, to simulate startup each morning, and 60 warm restarts, to simulate cloud cover transients. The behavior of the cold and warm starts showed no significant changes during the life test. In the experiments, the fluid/surface combination provided stable, high-performance boiling at the operating temperature of 700 C. Based on these experiments, a pool boiler was designed for a full-scale 25-kWe Stirling system.

How much might additional half a degree from a global warming of 1.5°C affects the extreme precipitation change in China?

NASA Astrophysics Data System (ADS)

Li, W.; Jiang, Z.

2017-12-01

In order to strengthen the global respond to the dangerous of global warming, Paris Agreement sets out two long-term warming goals: limiting global warming to well below 2˚C and purse effort to below 1.5˚C above pre-industrial levels. However, future climate change risks in those two warming targets show significant regional differences. This article aims to study the intensity and frequency of extreme precipitation change over China under those two global warming targets by using CMIP5 models under RCP4.5 and RCP8.5 scenario. Focus is put on the effects of the additional half degree in changing the extreme precipitation. Results show that the changes of extreme precipitation are independent of the RCP scenarios when global warming reaches the same threshold. Intensity of extreme precipitation averaged over China increase by around 6% and 11% when global warming reaches 1.5˚C and 2˚C, respectively. The additional half a degree increase makes the intensity of extreme precipitation averaged over China to increase by 4.5%, which translates to an increase close to the Clausius-Clapeyron scaling. Return period decreases by 5 years for the extra half degree warming when the 20-year return values are considered at the reference level.

Predicting "Hot" and "Warm" Spots for Fragment Binding.

PubMed

Rathi, Prakash Chandra; Ludlow, R Frederick; Hall, Richard J; Murray, Christopher W; Mortenson, Paul N; Verdonk, Marcel L

2017-05-11

Computational fragment mapping methods aim to predict hotspots on protein surfaces where small fragments will bind. Such methods are popular for druggability assessment as well as structure-based design. However, to date researchers developing or using such tools have had no clear way of assessing the performance of these methods. Here, we introduce the first diverse, high quality validation set for computational fragment mapping. The set contains 52 diverse examples of fragment binding "hot" and "warm" spots from the Protein Data Bank (PDB). Additionally, we describe PLImap, a novel protocol for fragment mapping based on the Protein-Ligand Informatics force field (PLIff). We evaluate PLImap against the new fragment mapping test set, and compare its performance to that of simple shape-based algorithms and fragment docking using GOLD. PLImap is made publicly available from https://bitbucket.org/AstexUK/pli .

Bracketing mid-pliocene sea surface temperature: maximum and minimum possible warming

USGS Publications Warehouse

Dowsett, Harry

2004-01-01

Estimates of sea surface temperature (SST) from ocean cores reveal a warm phase of the Pliocene between about 3.3 and 3.0 Mega-annums (Ma). Pollen records from land based cores and sections, although not as well dated, also show evidence for a warmer climate at about the same time. Increased greenhouse forcing and altered ocean heat transport is the leading candidates for the underlying cause of Pliocene global warmth. However, despite being a period of global warmth, there exists considerable variability within this interval. Two new SST reconstructions have been created to provide a climatological error bar for warm peak phases of the Pliocene. These data represent the maximum and minimum possible warming recorded within the 3.3 to 3.0 Ma interval.

Solar Evolution and Climate on the Terrestrial Planets

NASA Astrophysics Data System (ADS)

Kasting, J. F.

2008-12-01

Venus, Earth, and Mars followed different evolutionary paths, partly because of their relative distance from the Sun, and partly because of the differences in their masses. Venus was too close to the Sun to retain its water, despite reduced solar luminosity early in Solar System history (1). The loss of water, followed by the buildup of CO2 in its atmosphere, led to the atmosphere that we see today. Earth was within the liquid water regime throughout its history. However, it must have had a larger greenhouse effect in the past in order to compensate for the faint young Sun. A combination of CO2, H2O, CH4, and C2H6 may have helped keep it warm (2,3). Mars' surface appears to have been wet early in its history, although opinions differ on how warm it must have been (4-6). CO2 and H2O alone could not have kept Mars' surface above freezing during Mars' early history when most of the large-scale fluvial features are thought to have formed (7). SO2 has been suggested as an additional greenhouse gas (8), but new calculations show that it would likely have been insufficient. Other mechanisms for warming early Mars may exist, however. Mars' albedo could have been significantly lowered by the presence of trace gases that absorb visible sunlight. NO2, which has a broad absorption peak centered at 400 nm, is a good candidate. A 3- bar CO2 atmosphere containing 30 ppm of NO2 could have kept Mars' mean surface temperature well above the freezing point of water at 3.8 Ga. Plausible sources of nitrogen oxides on early Mars include lightning and impacts. Other visible/UV-absorbing trace gases may have added to this warming. Thus, a complex mixture of gases could have helped keep early Mars warm. References: 1. J.F. Kasting, Icarus 74, 472 (1988). 2. A.A. Pavlov et al., J. Geophys. Res. 105, 11 (2000). 3. J.D. Haqq-Misra et al., Astrobiol. (in press). 4. J.B. Pollack et al., Icarus 71, 203 (1987). 5. T.L. Segura, O.B. Toon, A. Colaprete et al., Science 298, 1977 (2002). 6. C.P. McKay, J. Phys. IV 121, 283 (2004). 7. J.F. Kasting, Icarus 94, 1 (1991). 8. I. Halevy et al. Science 318, 1903 (2007).

Recent surface cooling in the Yellow and East China Seas and the associated North Pacific climate regime shift

NASA Astrophysics Data System (ADS)

Kim, Yong Sun; Jang, Chan Joo; Yeh, Sang-Wook

2018-03-01

The Yellow and East China Seas (YECS) are widely believed to have experienced robust, basin-scale warming over the last few decades. However, the warming reached a peak in the late 1990s, followed by a significant cooling trend. In this study, we investigated the characteristics of this low-frequency sea surface temperature (SST) variance and its dynamic relationship with large-scale climate variability through cyclostationary orthogonal function analysis for the 1982-2014 period. Both regressed surface winds on the primary mode of the YECS SST and trends in air-sea heat fluxes demonstrate that the intensification of the northerly winds in winter contribute largely to the recent cooling trend by increasing heat loss to the atmosphere. As a localized oceanic response to these winds, the upwind flow seems to bring warm waters and partially counteracts the basin-scale cooling, thus contributing to a weakening of the cooling trend along the central trough of the Yellow Sea. In the context of the large-scale climate variabilities, a strong relationship between the YECS SST variability and Pacific Decadal Oscillation (PDO) became weak considerably during the recent cooling period after the late 1990s as the PDO signals appeared to be confined within the eastern basin of the North Pacific in association with the regime shift. In addition to this decoupling of the YECS SST from the PDO, the intensifying Siberian High pressure system likely caused the enhanced northerly winds, leading to the recent cooling trend. These findings highlight relative roles of the PDO and the Siberian High in shaping the YECS SST variance through the changes in the large-scale atmospheric circulation and attendant oceanic advection.

Global satellite data highlights the diurnal asymmetry of the surface temperature response to deforestation

NASA Astrophysics Data System (ADS)

Schultz, Natalie M.; Lawrence, Peter J.; Lee, Xuhui

2017-04-01

Uncertainties remain about the spatial pattern and magnitude of the biophysical effects of deforestation. In particular, a diurnal asymmetry in the magnitude and sign of the surface temperature response to deforestation (ΔTS) has been observed, but the biophysical processes that contribute to day and nighttime ΔTS are not fully understood. In this study, we use a space-for-time approach with satellite and reanalysis data to investigate the biophysical processes that control the day and nighttime ΔTS. Additionally, we incorporate flux-tower data to examine two hypotheses for nighttime forest warming relative to open lands: (1) that forests generate turbulence in the stable nocturnal boundary layer, which brings heat aloft down to the surface, and (2) that forests store more heat during the day and release it at night. Our results confirm a diurnal asymmetry in ΔTS. Over most regions of the world, deforestation results in daytime warming and nighttime cooling. The strongest daytime warming is in the tropics, where the average ΔTS is 4.4 ± 0.07 K. The strongest nighttime cooling is observed in the boreal zone, where open lands are cooler than forests by an average of 1.4 ± 0.04 K. Daytime patterns of ΔTS are explained by differences in the latent heat flux (ΔLE) and absorbed solar radiation (ΔKa). We find that nighttime ΔTS is related to the strength of the nocturnal temperature inversion, with stronger temperature inversions at high latitudes and weak inversions in the tropics. Forest turbulence at night combined with stored heat release drives nighttime ΔTS patterns.

Impact of northern Eurasian snow cover in autumn on the warm Arctic-cold Eurasia pattern during the following January and its linkage to stationary planetary waves

NASA Astrophysics Data System (ADS)

Xu, Xinping; He, Shengping; Li, Fei; Wang, Huijun

2018-03-01

The connection between Eurasian snow cover (SC) in autumn and Eurasian winter mean surface air temperature (SAT) has been identified by many studies. However, some recent observations indicate that early and late winter climate sometimes shows an out-of-phase relationship, suggesting that the winter mean situation might obscure the important relationships that are relevant for scientific research and applications. This study investigates the relationship between October northern Eurasian SC (NESC; 58°-68°N, 30°-90°E) and Eurasian SAT during the winter months and finds a significant relationship only exists in January. Generally, following reduced October NESC, the East Asian trough and Ural high are intensified in January, and anomalous northeasterly winds prevail in mid-latitudes, causing cold anomalies over Eurasia. Meanwhile, anomalous southwesterly winds along the northern fringe of the Ural high favor warm anomalies in the Arctic. The dynamical mechanism for the connection between NESC in October and the warm Arctic-cold Eurasia (WACE) anomaly in January is further investigated from the perspective of quasi-stationary planetary wave activity. It is found that planetary waves with zonal wavenumber-1 (ZWN1) play a dominant role in this process. Specifically, the ZWN1 pattern of planetary-scale waves concurrent with October NESC anomaly extends from the surface to the upper-stratosphere. It persists in the stratosphere through November-December and propagates downward to the surface by the following January, making the connection between October NESC and January climate possible. Additionally, the influence of October NESC on the January WACE pattern has intensified since the early-2000s.

Possible signals of poleward surface ocean heat transport, of Arctic basal ice melt, and of the twentieth century solar maximum in the 1904-2012 Isle of Man daily timeseries

NASA Astrophysics Data System (ADS)

Matthews, J. B.; Matthews, J. B. R.

2014-01-01

This is the second of two papers on observational timeseries of top of ocean heat capture. The first reports hourly and daily meridional central tropical Pacific top 3 m timeseries showing high Southern Hemisphere evaporation (2.67 m yr-1) and Northern Hemisphere trapped heat (12 MJ m-2 day-1). We suggested that wind drift/geostrophic stratified gyre circulation transported warm water to the Arctic and led to three phases of Arctic basal ice melt and fluxes of brackish nutrient-rich waters to north Atlantic on centennial timescales. Here we examine daily top metre 1904-2012 timeseries at Isle of Man west coast ~54° N for evidence of tropical and polar surface waters. We compare these to Central England (CET) daily land-air temperatures and to Arctic floating ice heat content and extent. We find three phases of ocean surface heating consistent with basal icemelt buffering greenhouse gas warming until a regime shift post-1986 led to the modern surface temperature rise of ~1 °C in 20 yr. Three phases were: warming +0.018 °C yr-1 from 1904-1939, slight cooling -0.002 °C yr-11940-86 and strong warming +0.037 °C yr-1 1986-2012. For the same periods CET land-air showed: warming +0.015 °C yr-1, slight cooling -0.004 °C yr-1, about half SST warming at +0.018 °C yr-1. The mid-century cooling and a 1959/1963 hot/cold event is consistent with sunspot/solar radiation maximum 1923-2008 leading to record volumes of Arctic ice meltwater and runoff that peaked in 1962/3 British Isles extreme cold winter. The warming Arctic resulted in wind regime and surface water regime shifts post 1986. This coincides with the onset of rapid Arctic annual ice melt. Continued heat imbalance is likely to lead to tidewater glacier basal icemelt and future sealevel rise after remaining relatively stable over 4000 yr. Our work needs confirmation by further fieldwork concentrating on the dynamics and thermodynamics of ocean top 3 m that controls the 93 % anthropogenic global warming in the oceans. This may be done most cost-effectively through focussed multidisciplinary scientific research adaptively managed and funded.

Potential climatic impacts and reliability of very large-scale wind farms

NASA Astrophysics Data System (ADS)

Wang, C.; Prinn, R. G.

2010-02-01

Meeting future world energy needs while addressing climate change requires large-scale deployment of low or zero greenhouse gas (GHG) emission technologies such as wind energy. The widespread availability of wind power has fueled substantial interest in this renewable energy source as one of the needed technologies. For very large-scale utilization of this resource, there are however potential environmental impacts, and also problems arising from its inherent intermittency, in addition to the present need to lower unit costs. To explore some of these issues, we use a three-dimensional climate model to simulate the potential climate effects associated with installation of wind-powered generators over vast areas of land or coastal ocean. Using wind turbines to meet 10% or more of global energy demand in 2100, could cause surface warming exceeding 1 °C over land installations. In contrast, surface cooling exceeding 1 °C is computed over ocean installations, but the validity of simulating the impacts of wind turbines by simply increasing the ocean surface drag needs further study. Significant warming or cooling remote from both the land and ocean installations, and alterations of the global distributions of rainfall and clouds also occur. These results are influenced by the competing effects of increases in roughness and decreases in wind speed on near-surface turbulent heat fluxes, the differing nature of land and ocean surface friction, and the dimensions of the installations parallel and perpendicular to the prevailing winds. These results are also dependent on the accuracy of the model used, and the realism of the methods applied to simulate wind turbines. Additional theory and new field observations will be required for their ultimate validation. Intermittency of wind power on daily, monthly and longer time scales as computed in these simulations and inferred from meteorological observations, poses a demand for one or more options to ensure reliability, including backup generation capacity, very long distance power transmission lines, and onsite energy storage, each with specific economic and/or technological challenges.

Potential climatic impacts and reliability of very large-scale wind farms

NASA Astrophysics Data System (ADS)

Wang, C.; Prinn, R. G.

2009-09-01

Meeting future world energy needs while addressing climate change requires large-scale deployment of low or zero greenhouse gas (GHG) emission technologies such as wind energy. The widespread availability of wind power has fueled legitimate interest in this renewable energy source as one of the needed technologies. For very large-scale utilization of this resource, there are however potential environmental impacts, and also problems arising from its inherent intermittency, in addition to the present need to lower unit costs. To explore some of these issues, we use a three-dimensional climate model to simulate the potential climate effects associated with installation of wind-powered generators over vast areas of land or coastal ocean. Using wind turbines to meet 10% or more of global energy demand in 2100, could cause surface warming exceeding 1°C over land installations. In contrast, surface cooling exceeding 1°C is computed over ocean installations, but the validity of simulating the impacts of wind turbines by simply increasing the ocean surface drag needs further study. Significant warming or cooling remote from both the land and ocean installations, and alterations of the global distributions of rainfall and clouds also occur. These results are influenced by the competing effects of increases in roughness and decreases in wind speed on near-surface turbulent heat fluxes, the differing nature of land and ocean surface friction, and the dimensions of the installations parallel and perpendicular to the prevailing winds. These results are also dependent on the accuracy of the model used, and the realism of the methods applied to simulate wind turbines. Additional theory and new field observations will be required for their ultimate validation. Intermittency of wind power on daily, monthly and longer time scales as computed in these simulations and inferred from meteorological observations, poses a demand for one or more options to ensure reliability, including backup generation capacity, very long distance power transmission lines, and onsite energy storage, each with specific economic and/or technological challenges.

Interannual Variability of Regional Hadley Circulation Intensity Over Western Pacific During Boreal Winter and Its Climatic Impact Over Asia-Australia Region

NASA Astrophysics Data System (ADS)

Huang, Ruping; Chen, Shangfeng; Chen, Wen; Hu, Peng

2018-01-01

This study investigates interannual variability of boreal winter regional Hadley circulation over western Pacific (WPHC) and its climatic impacts. A WPHC intensity index (WPHCI) is defined as the vertical shear of the divergent meridional winds. It shows that WPHCI correlates well with the El Niño-Southern Oscillation (ENSO). To investigate roles of the ENSO-unrelated part of WPHCI (WPHCIres), variables that are linearly related to the Niño-3 index have been removed. It reveals that meridional sea surface temperature gradient over the western Pacific plays an essential role in modulating the WPHCIres. The climatic impacts of WPHCIres are further investigated. Below-normal (above-normal) precipitation appears over south China (North Australia) when WPHCIres is stronger. This is due to the marked convergence (divergence) anomalies at the upper troposphere, divergence (convergence) at the lower troposphere, and the accompanied downward (upward) motion over south China (North Australia), which suppresses (enhances) precipitation there. In addition, a pronounced increase in surface air temperature (SAT) appears over south and central China when WPHCIres is stronger. A temperature diagnostic analysis suggests that the increase in SAT tendency over central China is primarily due to the warm zonal temperature advection and subsidence-induced adiabatic heating. In addition, the increase in SAT tendency over south China is primarily contributed by the warm meridional temperature advection. Further analysis shows that the correlation of WPHCIres with the East Asian winter monsoon (EAWM) is weak. Thus, this study may provide additional sources besides EAWM and ENSO to improve understanding of the Asia-Australia climate variability.

Hydrogen Isotopes Record the History of the Martian Hydrosphere and Atmosphere

NASA Technical Reports Server (NTRS)

Usui, T.; Simon, J. I.; Jones, J. H.; Kurokawa, H.; Sato, M.; Alexander, C. M. O'D; Wang, J.

2015-01-01

The surface geology and geomorphology of Mars indicates that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. This study presents insights from hydrogen isotopes for the origin and evolution of Martian water reservoirs.

CAUSES: Attribution of Surface Radiation Biases in NWP and Climate Models near the U.S. Southern Great Plains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Weverberg, K.; Morcrette, C. J.; Petch, J.

Many numerical weather prediction (NWP) and climate models exhibit too warm lower tropospheres near the mid-latitude continents. This warm bias has been extensively studied before, but evidence about its origin remains inconclusive. Some studies point to deficiencies in the deep convective or low clouds. Other studies found an important contribution from errors in the land surface properties. The warm bias has been shown to coincide with important surface radiation biases that likely play a critical role in the inception or the growth of the warm bias. Documenting these radiation errors is hence an important step towards understanding and alleviating themore » warm bias. This paper presents an attribution study to quantify the net radiation biases in 9 model simulations, performed in the framework of the CAUSES project (Clouds Above the United States and Errors at the Surface). Contributions from deficiencies in the surface properties, clouds, integrated water vapor (IWV) and aerosols are quantified, using an array of radiation measurement stations near the ARM SGP site. Furthermore, an in depth-analysis is shown to attribute the radiation errors to specific cloud regimes. The net surface SW radiation is overestimated (LW underestimated) in all models throughout most of the simulation period. Cloud errors are shown to contribute most to this overestimation in all but one model, which has a dominant albedo issue. Using a cloud regime analysis, it was shown that missing deep cloud events and/or simulating deep clouds with too weak cloud-radiative effects account for most of these cloud-related radiation errors. Some models have compensating errors between excessive occurrence of deep cloud, but largely underestimating their radiative effect, while other models miss deep cloud events altogether. Surprisingly however, even the latter models tend to produce too much and too frequent afternoon surface precipitation. This suggests that rather than issues with the triggering of deep convection, the deep cloud problem in many models could be related to too weak convective cloud detrainment and too large precipitation efficiencies. This does not rule out that previously documented issues with the evaporative fraction contribute to the warm bias as well, since the majority of the models underestimate the surface rain rates overall, as they miss the observed large nocturnal precipitation peak.« less

Detecting climate forcing and feedback signals in surface climate change

NASA Astrophysics Data System (ADS)

Davy, Richard; Esau, Igor

2015-04-01

The Earth has warmed in the last century and a large component of that warming has been attributed to the build-up of anthropogenic greenhouse gases. There are also numerous feedback processes which can introduce strong, regionalized asymmetries to the overall warming trend. These processes alter the surface energy budget, and thus affect the surface air temperature, which is one of the primary measures of how the climate is changing. However, the degree to which a given forcing or feedback process alters surface temperatures is contingent on the effective heat capacity of the atmosphere which is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, which can lead to a strongly amplified temperature response in shallow boundary layers. Therefore, if a climate forcing or feedback is acting across a wide range of conditions of the boundary layer, then this non-linear response of the surface climate to perturbations in the forcing must be accounted for in order to correctly assess the effect of the forcing on the surface climatology.

Accelerated warming at high elevations: a review of the current evidence and proposals for future research (Invited)

NASA Astrophysics Data System (ADS)

Pepin, N. C.

2013-12-01

Arctic amplification, whereby enhanced warming is evident at high latitudes, is well accepted amongst the scientific community. Increased warming at high elevations is more controversial and is often given the more vague term 'elevational dependency'. The way in which different approaches (mountain surface data, radiosondes, satellite data and models) often yield different results is discussed, along with the differences between these approaches. Analyses of surface data differ in the stations chosen for comparison, the time period, elevational range, and methods of trend identification. An analysis of global datasets using over a thousand stations (GHCN, CRU) and defining change by the most common method of calculating the linear gradient of a best fit line (linear regression) shows no simple relationship between warming rate and elevation. There are however feedback mechanisms in the mountain environment (e.g. cryospheric change, water vapor and treelines) which, although they may enhance warming at certain elevations, are fairly poorly understood. Warming rates are also shown to be influenced by factors in the mountain environment other than elevation, including topography (aspect, slope, topographic exposure) as well as mean annual temperature, but the relative influences of such controls have yet to be disentangled from those that show a more simple elevationally-dependent signal. Mountain summits and exposed ridge sites are shown to show least variability in warming rates, rising up above a sea of noise. Radiosondes and satellite data are further removed from changes on the ground (surface temperatures) and studies using such data tend to be rather divorced from the mountain environment and need calibration/comparison with surface datasets. Reanalyses such as NCEP/NCAR and ERA, although having good spatial coverage, tend to suffer from the same problems. Following a discussion of differences between all these approaches, a plan to develop an integrated global approach to this issue will be discussed.

The basic thermodynamics of Earth's radiation budget

NASA Astrophysics Data System (ADS)

Ward, Peter L.

2015-04-01

The microscopic bonds that hold matter together oscillate about a potential energy minimum between attractive and repulsive electrostatic forces, giving rise to macroscopic temperature. When a body of matter reaches thermal equilibrium, the spectrum of frequencies and associated amplitudes of oscillation on the body's surface are described by Planck's empirical law, which shows that heating matter increases the amplitude of these oscillations at all frequencies and shifts the peak frequency to a higher value. The oscillating motion of charge on the surface of matter induces an electromagnetic field in air or space containing the same frequencies (colors) and amplitudes (brightness) flowing away from the surface just as a radio station transmits its frequency and amplitude. Numerous frequencies coexist in an electromagnetic field over a broad spectral range, but each frequency does not interact with any other frequencies and does not change as it propagates over galactic distances except for Doppler effects. Amplitudes (intensities, brightness), on the other hand, decrease by one over the square of the distance traveled as they spread out over the surface of an expanding sphere. Planck (1900) showed that in air and space radiant (thermal) energy at each frequency is equal to the frequency times a constant (E=hν), an expression used widely in photochemistry to designate the thermal energy required to cause a photochemical reaction. High-frequency ultraviolet radiation causes sunburn; lower frequency visible radiation powers photosynthesis; much lower frequency infrared radiation cannot cause either, no matter how large the amplitude or the amount. While many frequencies coexist in air or space, neither frequencies nor energies interact or are additive until in the presence of matter. According to E=hν, the solar, ultraviolet thermal energy that reaches Earth when ozone is depleted is at least 48 times more energetic (hotter) than infrared energy absorbed by greenhouse gases. There simply is not enough thermal energy absorbed by greenhouse gases to have a major effect on global warming. Computer programs used to quantify greenhouse-gas theory overestimate infrared energies because they assume that thermal energy travels in space as waves, for which energy is a function of amplitude squared, and that energies are additive over bandwidth, both properties that are very different from the observed behavior of radiation in the atmosphere. Heat only flows from hot to cold; it cannot flow from a colder layer in the atmosphere to a warmer Earth, as assumed in many radiation budgets (e.g. Wild et al., 2013); you cannot get warmer by standing next to a cold stove. According to Planck's Law, radiation from a body of matter does not have high enough frequencies or amplitudes to warm the same body, as is assumed by greenhouse-gas theory. Warming radiation must come from a warmer body. Detailed observations of global warming, including the recent hiatus, are explained much more directly and clearly by ozone depletion theory, where less ozone in the stratosphere allows more high-energy, solar ultraviolet radiation to reach Earth, cooling the stratosphere, warming the oceans. More details at ozonedepletiontheory.info plus a video at tinyurl.com/ozone-depletion-theory.

The response of Phanerozoic surface temperature to variations in atmospheric oxygen concentration

NASA Astrophysics Data System (ADS)

Payne, Rebecca C.; Britt, Amber V.; Chen, Howard; Kasting, James F.; Catling, David C.

2016-09-01

Recently, Poulsen et al. (2015) suggested that O2 has played a major role in climate forcing during the Phanerozoic. Specifically, they argued that decreased O2 levels during the Cenomanian stage of the middle Cretaceous (94-100 Ma) could help explain the extremely warm climate during that time. The postulated warming mechanism involves decreased Rayleigh scattering by a thinner atmosphere, which reduces the planetary albedo and allows greater surface warming. This warming effect is then amplified by cloud feedbacks within their 3-D climate model. This increase in shortwave surface forcing, in their calculations, exceeds any decrease in the greenhouse effect caused by decreased O2. Here we use a 1-D radiative-convective climate model (with no cloud feedback) to check their results. We also include a self-consistent calculation of the change in atmospheric ozone and its effect on climate. Our results are opposite to those of Poulsen et al.: we find that the climate warms by 1.4 K at 35% O2 concentrations as a result of increased pressure broadening of CO2 and H2O absorption lines and cools by 0.8 K at 10% O2 as a result of decreased pressure broadening. The surface temperature changes are only about 1 K either way, though, for reasonable variations in Phanerozoic O2 concentrations (10%-35% by volume). Hence, it seems unlikely that changes in atmospheric O2 account for the warm climate of the Cenomanian. Other factors, such as a higher-than-expected sensitivity of climate to increased CO2 concentrations, may be required to obtain agreement with the paleoclimate data.

Narrowing the surface temperature range in CMIP5 simulations over the Arctic

NASA Astrophysics Data System (ADS)

Hao, Mingju; Huang, Jianbin; Luo, Yong; Chen, Xin; Lin, Yanluan; Zhao, Zongci; Xu, Ying

2018-05-01

Much uncertainty exists in reproducing Arctic temperature using different general circulation models (GCMs). Therefore, evaluating the performance of GCMs in reproducing Arctic temperature is critically important. In our study, 32 GCMs in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) during the period 1900-2005 are used, and several metrics, i.e., bias, correlation coefficient ( R), and root mean square error (RMSE), are applied. The Cowtan data set is adopted as the reference data. The results suggest that the GCMs used can reasonably reproduce the Arctic warming trend during the period 1900-2005, as observed in the observational data, whereas a large variation of inter-model differences exists in modeling the Arctic warming magnitude. With respect to the reference data, most GCMs have large cold biases, whereas others have weak warm biases. Additionally, based on statistical thresholds, the models MIROC-ESM, CSIRO-Mk3-6-0, HadGEM2-AO, and MIROC-ESM-CHEM (bias ≤ ±0.10 °C, R ≥ 0.50, and RMSE ≤ 0.60 °C) are identified as well-performing GCMs. The ensemble of the four best-performing GCMs (ES4), with bias, R, and RMSE values of -0.03 °C, 0.72, and 0.39 °C, respectively, performs better than the ensemble with all 32 members, with bias, R, and RMSE values of -0.04 °C, 0.64, and 0.43 °C, respectively. Finally, ES4 is used to produce projections for the next century under the scenarios of RCP2.6, RCP4.5, and RCP8.0. The uncertainty in the projected temperature is greater in the higher emissions scenarios. Additionally, the projected temperature in the cold half year has larger variations than that in the warm half year.

Inter-Relationship Between Subtropical Pacific Sea Surface Temperature, Arctic Sea Ice Concentration, and the North Atlantic Oscillation in Recent Summers and Winters

NASA Technical Reports Server (NTRS)

Lim, Young-Kwon; Cullather, Richard I.; Nowicki, Sophie M.; Kim, Kyu-Myong

2017-01-01

The inter-relationship between subtropical western-central Pacific sea surface temperatures (STWCPSST), sea ice concentration in the Beaufort Sea (SICBS), and the North Atlantic Oscillation (NAO) are investigated for the last 37 summers and winters (1980-2016). Lag-correlation of the STWCPSST×(-1) in spring with the NAO phase and SICBS in summer increases over the last two decades, reaching r = 0.4-0.5 with significance at 5 percent, while winter has strong correlations in approximately 1985-2005. Observational analysis and the atmospheric general circulation model experiments both suggest that STWCPSST warming acts to increase the Arctic geopotential height and temperature in the following season. This atmospheric response extends to Greenland, providing favorable conditions for developing the negative phase of the NAO. SIC and surface albedo tend to decrease over the Beaufort Sea in summer, linked to the positive surface net shortwave flux. Energy balance considering radiative and turbulent fluxes reveal that available energy that can heat surface is larger over the Arctic and Greenland and smaller over the south of Greenland, in response to the STWCPSST warming in spring. XXXX Arctic & Atlantic: Positive upper-level height/T anomaly over the Arctic and Greenland, and a negative anomaly over the central-eastern Atlantic, resembling the (-) phase of the NAO. Pacific: The negative height/T anomaly over the mid-latitudes, along with the positive anomaly over the STWCP, where 1degC warming above climatology is prescribed. Discussion: It is likely that the Arctic gets warm and the NAO is in the negative phase in response to the STWCP warming. But, there are other factors (e.g., internal variability) that contribute to determination of the NAO phase: not always the negative phase of the NAO in the event of STWCP warming (e.g.: recent winters and near neutral NAO in 2017 summer).

The Tropical Western Hemisphere Warm Pool

NASA Astrophysics Data System (ADS)

Wang, C.; Enfield, D. B.

2002-12-01

The paper describes and examines variability of the tropical Western Hemisphere warm pool (WHWP) of water warmer than 28.5oC. The WHWP is the second-largest tropical warm pool on Earth. Unlike the Eastern Hemisphere warm pool in the western Pacific, which straddles the equator, the WHWP is entirely north of the equator. At various stages of development the WHWP extends over parts of the eastern North Pacific, the Gulf of Mexico, the Caribbean, and the western tropical North Atlantic. It has a large seasonal cycle and its interannual fluctuations of area and intensity are significant. Surface heat fluxes warm the WHWP through the boreal spring to an annual maximum of SST and WHWP area in the late summer/early fall, associated with eastern North Pacific and Atlantic hurricane activities and rainfall from northern South America to the southern tier of the United States. Observations suggest that a positive ocean-atmosphere feedback operating through longwave radiation and associated cloudiness seems to operate in the WHWP. During winter preceding large warm pool, there is an alteration of the Walker and Hadley circulation cells that serves as a "tropospheric bridge" for transferring Pacific ENSO effects to the Atlantic sector and inducing initial warming of warm pool. Associated with the warm SST anomalies is a decrease in sea level pressure anomalies and an anomalous increase in atmospheric convection and cloudiness. The increase in convective activity and cloudiness results in less net longwave radiation loss from the sea surface, which then reinforces SST anomalies.

Centuries of intense surface melt on Larsen C Ice Shelf

NASA Astrophysics Data System (ADS)

Bevan, Suzanne L.; Luckman, Adrian; Hubbard, Bryn; Kulessa, Bernd; Ashmore, David; Kuipers Munneke, Peter; O'Leary, Martin; Booth, Adam; Sevestre, Heidi; McGrath, Daniel

2017-12-01

Following a southward progression of ice-shelf disintegration along the Antarctic Peninsula (AP), Larsen C Ice Shelf (LCIS) has become the focus of ongoing investigation regarding its future stability. The ice shelf experiences surface melt and commonly features surface meltwater ponds. Here, we use a flow-line model and a firn density model (FDM) to date and interpret observations of melt-affected ice layers found within five 90 m boreholes distributed across the ice shelf. We find that units of ice within the boreholes, which have densities exceeding those expected under normal dry compaction metamorphism, correspond to two climatic warm periods within the last 300 years on the Antarctic Peninsula. The more recent warm period, from the 1960s onwards, has generated distinct sections of dense ice measured in two boreholes in Cabinet Inlet, which is close to the Antarctic Peninsula mountains - a region affected by föhn winds. Previous work has classified these layers as refrozen pond ice, requiring large quantities of mobile liquid water to form. Our flow-line model shows that, whilst preconditioning of the snow began in the late 1960s, it was probably not until the early 1990s that the modern period of ponding began. The earlier warm period occurred during the 18th century and resulted in two additional sections of anomalously dense ice deep within the boreholes. The first, at 61 m in one of our Cabinet Inlet boreholes, consists of ice characteristic of refrozen ponds and must have formed in an area currently featuring ponding. The second, at 69 m in a mid-shelf borehole, formed at the same time on the edge of the pond area. Further south, the boreholes sample ice that is of an equivalent age but which does not exhibit the same degree of melt influence. This west-east and north-south gradient in the past melt distribution resembles current spatial patterns of surface melt intensity.

The recent warming trend in North Greenland

USGS Publications Warehouse

Orsi, Anais J.; Kawamura, Kenji; Masson-Delmotte, Valerie; Fettweis, Xavier; Box, Jason E.; Dahl-Jensen, Dorthe; Clow, Gary D.; Landais, Amaelle; Severinghaus, Jeffrey P.

2017-01-01

The Arctic is among the fastest warming regions on Earth, but it is also one with limited spatial coverage of multidecadal instrumental surface air temperature measurements. Consequently, atmospheric reanalyses are relatively unconstrained in this region, resulting in a large spread of estimated 30 year recent warming trends, which limits their use to investigate the mechanisms responsible for this trend. Here we present a surface temperature reconstruction over 1982–2011 at NEEM (North Greenland Eemian Ice Drilling Project, 51°W, 77°N), in North Greenland, based on the inversion of borehole temperature and inert gas isotope data. We find that NEEM has warmed by 2.7 ± 0.33°C over the past 30 years, from the long-term 1900–1970 average of −28.55 ± 0.29°C. The warming trend is principally caused by an increase in downward longwave heat flux. Atmospheric reanalyses underestimate this trend by 17%, underlining the need for more in situ observations to validate reanalyses.

Influences of spring-to-summer sea surface temperatures over different Indian Ocean domains on the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Li, Zhenning; Yang, Song

2017-11-01

The influences of spring-to-summer sea surface temperature (SST) anomalies in different domains of the Indian Ocean (IO) on the Asian summer monsoon are investigated by conducting a series of numerical experiments using the NCAR CAM4 model. It is found that, to a certain extent, the springtime IO SST anomalies can persist to the summer season. The spring-to-summer IO SST anomalies associated with the IO basin warming mode are strongly linked to the summer climate over Asia, especially the South Asian monsoon (SAM) and the East Asian monsoon. Among this connection, the warming of tropical IO plays the most critical role, and the warming of southern IO is important for monsoon variation and prediction prior to the full development of the monsoon. The atmospheric response to IO basin wide warming is similar with that to tropical IO warming. The influence of northern IO warming on the SAM, however, is opposite to the effect of southern IO warming. Meanwhile, the discrepancies between the results from idealized SST forcing simulations and observations, especially for the southern IO, reveal that the dominant role of air-sea interaction in the monsoon-IO coupled system cannot be ignored. Moreover, the springtime northern IO warming seems to favor an early onset or a stronger persistence of the SAM.

Northern North Atlantic Sea Surface Height and Ocean Heat Content Variability

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Rhines, Peter; Worthen, Denise L.

2013-01-01

The evolution of nearly 20 years of altimetric sea surface height (SSH) is investigated to understand its association with decadal to multidecadal variability of the North Atlantic heat content. Altimetric SSH is dominated by an increase of about 14 cm in the Labrador and Irminger seas from 1993 to 2011, while the opposite has occurred over the Gulf Stream region over the same time period. During the altimeter period the observed 0-700 m ocean heat content (OHC) in the subpolar gyre mirrors the increased SSH by its dominantly positive trend. Over a longer period, 1955-2011, fluctuations in the subpolar OHC reflect Atlantic multidecadal variability (AMV) and can be attributed to advection driven by the wind stress ''gyre mode'' bringing more subtropical waters into the subpolar gyre. The extended subpolar warming evident in SSH and OHC during the altimeter period represents transition of the AMV from cold to warm phase. In addition to the dominant trend, the first empirical orthogonal function SSH time series shows an abrupt change 2009-2010 reaching a new minimum in 2010. The change coincides with the change in the meridional overturning circulation at 26.5N as observed by the RAPID (Rapid Climate Change) project, and with extreme behavior of the wind stress gyre mode and of atmospheric blocking. While the general relationship between northern warming and Atlantic meridional overturning circulation (AMOC) volume transport remains undetermined, the meridional heat and salt transport carried by AMOC's arteries are rich with decade-to-century timescale variability.

The impact of an extreme case of irrigation on the southeastern United States climate

NASA Astrophysics Data System (ADS)

Selman, Christopher; Misra, Vasubandhu

2017-02-01

The impacts of irrigation on southeast United States diurnal climate are investigated using simulations from a regional climate model. An extreme case is assumed, wherein irrigation is set to 100 % of field capacity over the growing season of May through October. Irrigation is applied to the root zone layers of 10-40 and 40-100 cm soil layers only. It is found that in this regime there is a pronounced decrease in monthly averaged temperatures in irrigated regions across all months. In non-irrigated areas a slight warming is simulated. Diurnal maximum temperatures in irrigated areas warm, while diurnal minimum temperatures cool. The daytime warming is attributed to an increase in shortwave flux at the surface owing to diminished low cloud cover. Nighttime and daily mean cooling result as a consequence repartitioning of energy into latent heat flux over sensible heat flux, and of a higher net downward ground heat flux. Excess heat is transported into the deep soil layer, preventing a rapidly intensifying positive feedback loop. Both diurnal and monthly average precipitations are reduced over irrigated areas at a magnitude and spatial pattern similar to one another. Due to the excess moisture availability, evaporation is seen to increase, but this is nearly balanced by a corresponding reduction in sensible heat flux. Concomitant with additional moisture availability is an increase in both transient and stationary moisture flux convergences. However, despite the increase, there is a large-scale stabilization of the atmosphere stemming from a cooled surface.

Hydrographic Conditions in the Gulf of Carpentaria During Australian Monsoon Experiment

NASA Astrophysics Data System (ADS)

Inoue, M.; Steinberg, C.; Wolanski, E.; Ridd, P.

2002-12-01

Gulf of Carpentaria located in the northern Australia, is a shallow wide basin with the deepest bottom depths of approximately 60 m. It is connected to Arafura Sea to the north and west, and to the Torres Strait to the east. Hydrographic surveys of the Gulf of Carpentaria were carried out in January and March, 1987 as part of Australian Monsoon Experiment. During the January survey, Tropical Cyclone (TC) Irma was formed in the Gulf of Carpentaria. An east-west CTD section at 13o52'S was occupied twice, one prior to and during, and the other after the formation of TC Irma. In addition, two post-Irma east-west sections were occupied at 12o40'S and 11o30'S. The pre-cyclone section indicates a well-defined stratified two-layer system, while the post-cyclone sections show deepening of the surface warm layer due to significant mixing by TC Irma. Overall, significant cooling of near surface warm water on the order of more than 1oC was observed. Significant heat loss estimated for the water column has presumably contributed toward the development of TC Irma. In February 1987, TC Jason was formed in the gulf. During the March survey, two east-west CTD sections were occupied at 11o30'S and 13o52'S. The March survey reveals notable warming of the bottom water. Detailed discussion of the CTD data from the two cruises will be presented.

Liver transplantation in man: morphometric analysis of the parenchymal alterations following cold ischaemia and warm ischaemia/reperfusion

PubMed Central

VIZZOTTO, LAURA; VERTEMATI, MAURIZIO; DEGNA, CARLO TOMMASINI; ASENI, PAOLO

2001-01-01

Ischaemia and reperfusion phases represent critical events during liver transplantation. The purpose of this study was to describe morphological alterations of both vascular and parenchymal compartments after ischaemia and reperfusion and to evaluate the possible relationship between morphometric parameters and biochemical/clinical data. Three needle biopsies were drawn from 20 patients who underwent orthotopic liver transplantation. The first biopsy was taken before flushing with preservation solution, and the second and the third to evaluate respectively the effects of cold ischaemia and of warm ischaemia/reperfusion. Biopsies were examined by an image analyser and morphometric parameters related to the liver parenchyma were evaluated. At the second biopsy we observed a decrease of the endothelium volume fraction while the same parameter referred to the sinusoidal lumen achieved a peak value. The hepatocytes showed a lower surface parenchymal/vascular sides ratio. This parameter was reversed at the end of the reperfusion phase; furthermore the third biopsy revealed endothelial swelling and a decreased volume fraction of the sinusoidal lumen. The results quantify the damage to the sinusoidal bed which, as already known, is one of the main targets of cold ischaemia; warm ischaemia and reperfusion accentuate endothelial damage. The end of transplantation is characterised by damage chiefly to parenchymal cells. Hepatocytes show a rearrangement of their surface sides, probably related to the alterations of the sinusoidal bed. In addition, the fluctuations of morphometric parameters during ischaemia/reperfusion correlate positively with biochemical data and clinical course of the patients. PMID:11430699

Methane Cycling in a Warming Wetland

NASA Astrophysics Data System (ADS)

Noyce, G. L.; Megonigal, P.; Rich, R.; Kirwan, M. L.; Herbert, E. R.

2017-12-01

Coastal wetlands are global hotspots of carbon (C) storage, but the future of these systems is uncertain. In June 2016, we initiated an in-situ, active, whole-ecosystem warming experiment in the Smithsonian's Global Change Research Wetland to quantify how warming and elevated CO2 affect the stability of coastal wetland soil C pools and contemporary rates of C sequestration. Transects are located in two plant communities, dominated by C3 sedges or C4 grasses. The experiment has a gradient design with air and soil warming treatments ranging from ambient to +5.1 °C and heated plots consistently maintain their target temperature year-round. In April 2017, an elevated CO2 treatment was crossed with temperature in the C3community. Ongoing measurements include soil elevation, C fluxes, porewater chemistry and redox potential, and above- and below-ground growth and biomass. In both years, warming increased methane (CH4) emissions (measured at 3-4 week intervals) from spring through fall at the C3 site, but had little effect on emissions from the C4 site. Winter (Dec-Mar) emissions showed no treatment effect. Stable isotope analysis of dissolved CH4 and DIC also indicated that warming had differing effects on CH4 pathways in the two vegetation communities. To better understand temperature effects on rates of CH4 production and oxidation, 1 m soil cores were collected from control areas of the marsh in summer 2017 and incubated at temperatures ranging from 4 °C to 35 °C. Warming increased CH4 production and oxidation rates in surface samples and oxidation rates in the rooting zone samples from both sites, but temperature responses in deep (1 m) soil samples were minimal. In the surface and rooting zone samples, production rates were also consistently higher in C3 soils compared to C4 soils, but, contrary to our expectations, the temperature response was stronger in the C4 soils. However, oxidation in C3 rooting zone samples did have a strong temperature response. The ratio of CO2:CH4 decreased with increasing temperature in surface samples from both sites, indicating that anaerobic respiration in surface soil may become increasingly methanogenic with warming. In contrast, the rooting zone and deep soil samples showed the opposite trend, again suggesting that the soil profile will not respond consistently to warming.

Geophysical techniques for low enthalpy geothermal exploration in New Zealand

NASA Astrophysics Data System (ADS)

Soengkono, Supri; Bromley, Chris; Reeves, Robert; Bennie, Stewart; Graham, Duncan

2013-05-01

Shallow warm water resources associated with low enthalpy geothermal systems are often difficult to explore using geophysical techniques, mainly because the warm water creates an insufficient physical change from the host rocks to be easily detectable. In addition, often the system also has a limited or narrow size. However, appropriate use of geophysical techniques can still help the exploration and further investigation of low enthalpy geothermal resources. We present case studies on the use of geophysical techniques for shallow warm water explorations over a variety of settings in New Zealand (mostly in the North Island) with variable degrees of success. A simple and direct method for the exploration of warm water systems is shallow temperature measurements. In some New Zealand examples, measurements of near surface temperatures helped to trace the extent of deeper thermal water. The gravity method was utilised as a structural technique for the exploration of some warm water systems in New Zealand. Our case studies show the technique can be useful in identifying basement depths and tracing fault systems associated with the occurrence of hot springs. Direct current (DC) ground resistivity measurements using a variety of electrode arrays have been the most common method for the exploration of low enthalpy geothermal resources in New Zealand. The technique can be used to detect the extent of shallow warm waters that are more electrically conductive than the surrounding cold groundwater. Ground resistivity investigations using the electromagnetic (EM) techniques of audio magnetotellurics (AMT or shallow MT), controlled source audio magnetotellurics (CSAMT) and transient electromagnetic (TEM) methods have also been used. Highly conductive clays of thermal or sedimentary origin often limit the penetration depth of the resistivity techniques and can create some interpretation difficulties. Interpretation of resistivity anomalies needs to be treated in a site specific manner.

Total ozone and surface temperature correlations during 1972 - 1981

NASA Technical Reports Server (NTRS)

Parsons, C. L.

1983-01-01

Ten years of Dobson spectrophotometer total ozone measurements and surface temperature observations were used to construct monthly mean values of the two parameters. The variability of both parameters is greatest in the months of January and February. Indeed, in January there is an apparent correlation between high total ozone values and abnormally low surface temperatures. However, the correlation does not hold in February. By reviewing the history of stratospheric warmings during this period, it is argued that the ozone and surface temperature correlation is influenced by the advection or lack of advection of ozone rich arctic air resulting from sudden stratospheric warmings.

The effects of aircraft on climate and pollution. Part II: 20-year impacts of exhaust from all commercial aircraft worldwide treated individually at the subgrid scale.

PubMed

Jacobson, M Z; Wilkerson, J T; Naiman, A D; Lele, S K

2013-01-01

This study examines the 20-year impacts of emissions from all commercial aircraft flights worldwide on climate, cloudiness, and atmospheric composition. Aircraft emissions from each individual flight worldwide were modeled to evolve from the subgrid to grid scale with the global model described and evaluated in Part I of this study. Simulations with and without aircraft emissions were run for 20 years. Aircraft emissions were found to be responsible for -6% of Arctic surface global warming to date, -1.3% of total surface global warming, and -4% of global upper tropospheric warming. Arctic warming due to aircraft slightly decreased Arctic sea ice area. Longer simulations should result in more warming due to the further increase in CO2. Aircraft increased atmospheric stability below cruise altitude and decreased it above cruise altitude. The increase in stability decreased cumulus convection in favor of increased stratiform cloudiness. Aircraft increased total cloud fraction on average. Aircraft increased surface and upper tropospheric ozone by -0.4% and -2.5%, respectively and surface and upper-tropospheric peroxyacetyl nitrate (PAN) by -0.1% and -5%, respectively. Aircraft emissions increased tropospheric OH, decreasing column CO and CH4 by -1.7% and -0.9%, respectively. Aircraft emissions increased human mortality worldwide by -620 (-240 to 4770) deaths per year, with half due to ozone and the rest to particulate matter less than 2.5 micrometers in diameter (PM2.5).

Using Radiative Signatures to Diagnose the Cause of Warming Associated with the Californian Drought

NASA Astrophysics Data System (ADS)

Wolf, S.; Yin, D.; Roderick, M. L.

2016-12-01

California recently experienced among the worst droughts of the last century, with unprecedented precipitation deficits and record high temperatures. The dry conditions caused severe water shortages in one of the economically most important agricultural regions of the US, particularly in the Central Valley. It has been hypothesized that anthropogenic warming is increasing the likelihood of such extreme droughts in California, or more specifically, that these drought conditions are a consequence of warmer temperatures from the enhanced greenhouse effect. Process studies suggest, however, that increased temperatures during droughts are mostly a consequence of reduced evaporative cooling resulting from the reduction in precipitation. Here we use surface radiation components from NASA's Clouds and Earth's Radiant Energy Systems (CERES), climatic data and direct flux tower measurements to investigate the cause of warming associated with the recent Californian Drought. Based on radiative signatures and surface energy balance we show that the warmer temperatures were not associated with an enhanced greenhouse effect by anthropogenic warming. The radiative signature showed decreased longwave downward radiation during the water years 2013-2014 compared to the decadal mean of 2001-2012. Instead, increased solar downward radiation in combination with reduced evaporative cooling from water deficits enhanced surface temperatures and sensible heat transfer to the atmosphere. We conclude that the drought was not directly associated with warming by increased longwave downward radiation, and that there is no simple relation between warmer surface temperatures and drought.

Gaseous mercury fluxes in peatlands and the potential influence of climate change

NASA Astrophysics Data System (ADS)

Haynes, Kristine M.; Kane, Evan S.; Potvin, Lynette; Lilleskov, Erik A.; Kolka, Randall K.; Mitchell, Carl P. J.

2017-04-01

Climate change has the potential to significantly impact the stability of large stocks of mercury (Hg) stored in peatland systems due to increasing temperatures, altered water table regimes and subsequent shifts in vascular plant communities. However, the Hg exchange dynamics between the atmosphere and peatlands are not well understood. At the PEATcosm Mesocosm Facility in Houghton, Michigan, total gaseous Hg (TGM) fluxes were monitored in a subset of 1-m3 peat monoliths with altered water table positions (high and low) and vascular plant functional groups (sedge only, Ericaceae only or unmanipulated control) above the Sphagnum moss layer. At the SPRUCE bog in north-central Minnesota, TGM fluxes were measured from plots subjected to deep peat soil warming (up to +9 °C above ambient at a depth of 2 m). At PEATcosm, the strongest depositional trend was observed with the Low WT - sedge only treatment mesocosms with a mean TGM flux of -73.7 ± 6.3 ng m-2 d-1, likely due to shuttling of Hg to the peat at depth by aerenchymous tissues. The highest total leaf surface and tissue Hg concentrations were observed with the Ericaceae shrubs. A negative correlation between TGM flux and Ericaceae total leaf surface area suggests an influence of shrubs in controlling Hg exchange through stomatal uptake, surface sorption and potentially, peat shading. Surface peat total Hg concentrations are highest in treatments with greatest deposition suggesting deposition controls Hg accumulation in surface peat. Fluxes in the SPRUCE plots ranged from -45.9 ± 93.8 ng m-2 d-1 prior to the implementation of the deep warming treatments to -1.41 ± 27.1 ng m-2 d-1 once warming targets were achieved at depth and +10.2 ± 44.6 ng m-2 d-1 following prolonged deep soil warming. While these intervals did not differ significantly, a significant positive increase in the slope of the regression between flux and surface temperature was observed across the pre-treatment and warming periods. Shifts in vascular vegetation cover and peat warming as a result of climate change may significantly affect the dynamics of TGM fluxes between peatlands and the atmosphere.

Weird Warm Spot on Exoplanet

NASA Image and Video Library

2010-10-19

This frame from an animation based on NASA Spitzer Space Telescope data illustrates an unexpected warm spot on the surface of a gaseous exoplanet.The bright orange patches are the hottest part of the planet.

Diurnal warming in shallow coastal seas: Observations from the Caribbean and Great Barrier Reef regions

NASA Astrophysics Data System (ADS)

Zhu, X.; Minnett, P. J.; Berkelmans, R.; Hendee, J.; Manfrino, C.

2014-07-01

A good understanding of diurnal warming in the upper ocean is important for the validation of satellite-derived sea surface temperature (SST) against in-situ buoy data and for merging satellite SSTs taken at different times of the same day. For shallow coastal regions, better understanding of diurnal heating could also help improve monitoring and prediction of ecosystem health, such as coral reef bleaching. Compared to its open ocean counterpart which has been studied extensively and modeled with good success, coastal diurnal warming has complicating localized characteristics, including coastline geometry, bathymetry, water types, tidal and wave mixing. Our goal is to characterize coastal diurnal warming using two extensive in-situ temperature and weather datasets from the Caribbean and Great Barrier Reef (GBR), Australia. Results showed clear daily warming patterns in most stations from both datasets. For the three Caribbean stations where solar radiation is the main cause of daily warming, the mean diurnal warming amplitudes were about 0.4 K at depths of 4-7 m and 0.6-0.7 K at shallower depths of 1-2 m; the largest warming value was 2.1 K. For coral top temperatures of the GBR, 20% of days had warming amplitudes >1 K, with the largest >4 K. The bottom warming at shallower sites has higher daily maximum temperatures and lower daily minimum temperatures than deeper sites nearby. The averaged daily warming amplitudes were shown to be closely related to daily average wind speed and maximum insolation, as found in the open ocean. Diurnal heating also depends on local features including water depth, location on different sections of the reef (reef flat vs. reef slope), the relative distance from the barrier reef chain (coast vs. lagoon stations vs. inner barrier reef sites vs. outer rim sites); and the proximity to the tidal inlets. In addition, the influence of tides on daily temperature changes and its relative importance compared to solar radiation was quantified by calculating the ratio of power spectrum densities at the principal lunar semidiurnal M2 tide versus 24-hour cycle frequency representing mainly solar radiation forcing, i.e., (PSDM2/PSD24). Despite the fact that GBR stations are generally located at regions with large tidal changes, the tidal effects were modest: 80% of stations showed value of (PSDM2/PSD24) of less than 10%.

Uncertain impacts on economic growth when stabilizing global temperatures at 1.5°C or 2°C warming

PubMed Central

Schwarz, Moritz; Tang, Kevin; Haustein, Karsten; Allen, Myles R.

2018-01-01

Empirical evidence suggests that variations in climate affect economic growth across countries over time. However, little is known about the relative impacts of climate change on economic outcomes when global mean surface temperature (GMST) is stabilized at 1.5°C or 2°C warming relative to pre-industrial levels. Here we use a new set of climate simulations under 1.5°C and 2°C warming from the ‘Half a degree Additional warming, Prognosis and Projected Impacts' (HAPPI) project to assess changes in economic growth using empirical estimates of climate impacts in a global panel dataset. Panel estimation results that are robust to outliers and breaks suggest that within-year variability of monthly temperatures and precipitation has little effect on economic growth beyond global nonlinear temperature effects. While expected temperature changes under a GMST increase of 1.5°C lead to proportionally higher warming in the Northern Hemisphere, the projected impact on economic growth is larger in the Tropics and Southern Hemisphere. Accounting for econometric estimation and climate uncertainty, the projected impacts on economic growth of 1.5°C warming are close to indistinguishable from current climate conditions, while 2°C warming suggests statistically lower economic growth for a large set of countries (median projected annual growth up to 2% lower). Level projections of gross domestic product (GDP) per capita exhibit high uncertainties, with median projected global average GDP per capita approximately 5% lower at the end of the century under 2°C warming relative to 1.5°C. The correlation between climate-induced reductions in per capita GDP growth and national income levels is significant at the p < 0.001 level, with lower-income countries experiencing greater losses, which may increase economic inequality between countries and is relevant to discussions of loss and damage under the United Nations Framework Convention on Climate Change. This article is part of the theme issue ‘The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'. PMID:29610370

The Effect of Extratropical Warming Amplification on the Future Tropical Precipitation

NASA Astrophysics Data System (ADS)

Yoshimori, M.; Hamano, Y.; Abe-Ouchi, A.

2016-12-01

The Arctic warms much more than the rest of the world under relatively uniform radiative forcing. Recent observations verify this characteristics of global warming. On the other hand, previous studies based on paleo-proxy data and paleo- and idealized numerical experiments have indicated that asymmetric warming between the two hemispheres can impact on the distribution of tropical precipitation. It was suggested diagnostically that the Arctic warming amplification may become responsible for a part of the future precipitation change in the tropics. In the current study, we have conducted several sensitivity experiments that isolate the effect of remote warming on the tropical precipitation using an atmospheric general circulation model with a mixture of prescribed and predicted mixed-layer sea surface conditions, depending of the region. Additional experiments including ocean dynamics will also be presented. In a standard equilibrium experiment of doubling of atmospheric CO2 concentration (2xCO2), the Northern Hemisphere mid-high latitude (40-90ºN) warms by about 7ºC and precipitation change occurs mostly in the tropical Pacific (20ºS-20ºN). In the zonal average, the increase in precipitation is larger in the North than the South by about 0.5 mm/day and the peak latitude of precipitation shifted northward by about 1º. Sensitivity experiments were designed to amplify or suppress the Northern Hemisphere mid-high latitude warming to different levels and to allow for the tropics to respond freely to those perturbations. The perturbations of the mid-high latitude warming range from -5ºC to +7ºC from the standard 2xCO2 experiment, and precipitation change range from -160% to +160% relative to the difference between 2xCO2 and control experiments. The peak latitude of precipitation shifted northward from -1.5º to +2.5º, and it was verified that most of the change is contributed by the change in the Hadley circulation, rather than the change in the moisture amount in the atmosphere. The response is understood through the energy budget analysis.

Uncertain impacts on economic growth when stabilizing global temperatures at 1.5°C or 2°C warming.

PubMed

Pretis, Felix; Schwarz, Moritz; Tang, Kevin; Haustein, Karsten; Allen, Myles R

2018-05-13

Empirical evidence suggests that variations in climate affect economic growth across countries over time. However, little is known about the relative impacts of climate change on economic outcomes when global mean surface temperature (GMST) is stabilized at 1.5°C or 2°C warming relative to pre-industrial levels. Here we use a new set of climate simulations under 1.5°C and 2°C warming from the 'Half a degree Additional warming, Prognosis and Projected Impacts' (HAPPI) project to assess changes in economic growth using empirical estimates of climate impacts in a global panel dataset. Panel estimation results that are robust to outliers and breaks suggest that within-year variability of monthly temperatures and precipitation has little effect on economic growth beyond global nonlinear temperature effects. While expected temperature changes under a GMST increase of 1.5°C lead to proportionally higher warming in the Northern Hemisphere, the projected impact on economic growth is larger in the Tropics and Southern Hemisphere. Accounting for econometric estimation and climate uncertainty, the projected impacts on economic growth of 1.5°C warming are close to indistinguishable from current climate conditions, while 2°C warming suggests statistically lower economic growth for a large set of countries (median projected annual growth up to 2% lower). Level projections of gross domestic product (GDP) per capita exhibit high uncertainties, with median projected global average GDP per capita approximately 5% lower at the end of the century under 2°C warming relative to 1.5°C. The correlation between climate-induced reductions in per capita GDP growth and national income levels is significant at the p  < 0.001 level, with lower-income countries experiencing greater losses, which may increase economic inequality between countries and is relevant to discussions of loss and damage under the United Nations Framework Convention on Climate Change.This article is part of the theme issue 'The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'. © 2018 The Authors.

Uncertain impacts on economic growth when stabilizing global temperatures at 1.5°C or 2°C warming

NASA Astrophysics Data System (ADS)

Pretis, Felix; Schwarz, Moritz; Tang, Kevin; Haustein, Karsten; Allen, Myles R.

2018-05-01

Empirical evidence suggests that variations in climate affect economic growth across countries over time. However, little is known about the relative impacts of climate change on economic outcomes when global mean surface temperature (GMST) is stabilized at 1.5°C or 2°C warming relative to pre-industrial levels. Here we use a new set of climate simulations under 1.5°C and 2°C warming from the `Half a degree Additional warming, Prognosis and Projected Impacts' (HAPPI) project to assess changes in economic growth using empirical estimates of climate impacts in a global panel dataset. Panel estimation results that are robust to outliers and breaks suggest that within-year variability of monthly temperatures and precipitation has little effect on economic growth beyond global nonlinear temperature effects. While expected temperature changes under a GMST increase of 1.5°C lead to proportionally higher warming in the Northern Hemisphere, the projected impact on economic growth is larger in the Tropics and Southern Hemisphere. Accounting for econometric estimation and climate uncertainty, the projected impacts on economic growth of 1.5°C warming are close to indistinguishable from current climate conditions, while 2°C warming suggests statistically lower economic growth for a large set of countries (median projected annual growth up to 2% lower). Level projections of gross domestic product (GDP) per capita exhibit high uncertainties, with median projected global average GDP per capita approximately 5% lower at the end of the century under 2°C warming relative to 1.5°C. The correlation between climate-induced reductions in per capita GDP growth and national income levels is significant at the p < 0.001 level, with lower-income countries experiencing greater losses, which may increase economic inequality between countries and is relevant to discussions of loss and damage under the United Nations Framework Convention on Climate Change. This article is part of the theme issue `The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'.

Improved atmosphere-ocean coupled modeling in the tropics for climate prediction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Minghua

2015-01-01

We investigated the initial development of the double ITCZ in the Community Climate System Model (CCSM Version 3) in the central Pacific. Starting from a resting initial condition of the ocean in January, the model developed a warm bias of sea-surface temperature (SST) in the central Pacific from 5oS to 10oS in the first three months. We found this initial bias to be caused by excessive surface shortwave radiation that is also present in the standalone atmospheric model. The initial bias is further amplified by biases in both surface latent heat flux and horizontal heat transport in the upper ocean.more » These biases are caused by the responses of surface winds to SST bias and the thermocline structure to surface wind curls. We also showed that the warming biases in surface solar radiation and latent heat fluxes are seasonally offset by cooling biases from reduced solar radiation after the austral summer due to cloud responses and in the austral fall due to enhanced evaporation when the maximum SST is closest to the equator. The warming biases from the dynamic heat transport by ocean currents however stay throughout all seasons once they are developed, which are eventually balanced by enhanced energy exchange and penetration of solar radiation below the mixed layer. Our results also showed that the equatorial cold tongue develops after the warm biases in the south central Pacific, and the overestimation of surface shortwave radiation recurs in the austral summer in each year.« less

Warm ocean surface led to ice margin retreat in central-eastern Baffin Bay during the Younger Dryas

NASA Astrophysics Data System (ADS)

Oksman, Mimmi; Weckström, Kaarina; Miettinen, Arto; Juggins, Stephen; Divine, Dmitry; Jackson, Rebecca; Korsgaard, Niels J.; Telford, Richard; Kucera, Michal

2017-04-01

The Greenland ice sheet stability is linked to fast-flowing ice streams that are influenced by sea surface temperatures (SSTs) at their front. One of the largest ice streams in West Greenland is the Jakobshavn Isbræ, which has been shown to have collapsed at ca. 12.2 kyr BP in the middle of the Younger Dryas (YD) cold period (12.9-11.7 kyr BP). The cause for this collapse is still unknown yet hypotheses, such as warm Atlantic water inflow, have been put forward to explain it. Here we present the first diatom-based high-resolution reconstruction of sea surface conditions in the central-eastern Baffin Bay between 14.0 and 10.2 kyr BP. The sea surface temperatures reveal warmer conditions beginning at ca. 13.4 kyr BP and leading to intensive calving and iceberg discharge from Jakobshavn Isbræ visible as increased sedimentation rates and deposition of coarse-grained material in our sediment stratigraphy. The warm YD ocean surface conditions in Baffin Bay are out of phase with the δ18O record from the North Greenland Ice Core Project (NGRIP) and other SST records from northern North-Atlantic. We show that the ocean has had significant interactions with the Greenland ice sheet in the past and emphasize its importance under the current warming of the North Atlantic.

Enhanced Surface Warming and Accelerated Snow Melt in the Himalayas and Tibetan Plateau Induced by Absorbing Aerosols

NASA Technical Reports Server (NTRS)

Lau, William K.; Kim, Maeng-Ki; Kim, Kyu-Myong; Lee, Woo-Seop

2010-01-01

Numerical experiments with the NASA finite-volume general circulation model show that heating of the atmosphere by dust and black carbon can lead to widespread enhanced warming over the Tibetan Plateau (TP) and accelerated snow melt in the western TP and Himalayas. During the boreal spring, a thick aerosol layer, composed mainly of dust transported from adjacent deserts and black carbon from local emissions, builds up over the Indo-Gangetic Plain, against the foothills of the Himalaya and the TP. The aerosol layer, which extends from the surface to high elevation (approx.5 km), heats the mid-troposphere by absorbing solar radiation. The heating produces an atmospheric dynamical feedback the so-called elevated-heat-pump (EHP) effect, which increases moisture, cloudiness, and deep convection over northern India, as well as enhancing the rate of snow melt in the Himalayas and TP. The accelerated melting of snow is mostly confined to the western TP, first slowly in early April and then rapidly from early to mid-May. The snow cover remains reduced from mid-May through early June. The accelerated snow melt is accompanied by similar phases of enhanced warming of the atmosphere-land system of the TP, with the atmospheric warming leading the surface warming by several days. Surface energy balance analysis shows that the short-wave and long-wave surface radiative fluxes strongly offset each other, and are largely regulated by the changes in cloudiness and moisture over the TP. The slow melting phase in April is initiated by an effective transfer of sensible heat from a warmer atmosphere to land. The rapid melting phase in May is due to an evaporation-snow-land feedback coupled to an increase in atmospheric moisture over the TP induced by the EHP effect.

Large ground surface temperature changes of the last three centuries inferred from borehole temperatures in the Southern Canadian Prairies, Saskatchewan

NASA Astrophysics Data System (ADS)

Majorowicz, Jacek A.; Safanda, Jan; Harris, Robert N.; Skinner, Walter R.

1999-05-01

New temperature logs in wells located in the grassland ecozone in the Southern Canadian Prairies in Saskatchewan, where surface disturbance is considered minor, show a large curvature in the upper 100 m. The character of this curvature is consistent with ground surface temperature (GST) warming in the 20th century. Repetition of precise temperature logs in southern Saskatchewan (years 1986 and 1997) shows the conductive nature of warming of the subsurface sediments. The magnitude of surface temperature change during that time (11 years) is high (0.3-0.4°C). To assess the conductive nature of temperature variations at the grassland surface interface, several precise air and soil temperature time series in the southern Canadian Prairies (1965-1995) were analyzed. The combined anomalies correlated at 0.85. Application of the functional space inversion (FSI) technique with the borehole temperature logs and site-specific lithology indicates a warming to date of approximately 2.5°C since a minimum in the late 18th century to mid 19th century. This warming represents an approximate increase from 4°C around 1850 to 6.5°C today. The significance of this record is that it suggests almost half of the warming occurred prior to 1900, before dramatic build up of atmospheric green house gases. This result correlates well with the proxy record of climatic change further to the north, beyond the Arctic Circle [Overpeck, J., Hughen, K., Hardy, D., Bradley, R., Case, R., Douglas, M., Finney, B., Gajewski, K., Jacoby, G., Jennings, A., Lamourex, S., Lasca, A., MacDonald, G., Moore, J., Retelle, M., Smith, S., Wolfe, A., Zielinski, G., 1997. Arctic environmental change of the last four centuries, Science 278, 1251-1256.].

Surface formation, preservation, and history of low-porosity crusts at the WAIS Divide site, West Antarctica

NASA Astrophysics Data System (ADS)

Fegyveresi, John M.; Alley, Richard B.; Muto, Atsuhiro; Orsi, Anaïs J.; Spencer, Matthew K.

2018-01-01

Observations at the West Antarctic Ice Sheet (WAIS) Divide site show that near-surface snow is strongly altered by weather-related processes such as strong winds and temperature fluctuations, producing features that are recognizable in the deep ice core. Prominent glazed surface crusts develop frequently at the site during summer seasons. Surface, snow pit, and ice core observations made in this study during summer field seasons from 2008-2009 to 2012-2013, supplemented by automated weather station (AWS) data with short- and longwave radiation sensors, revealed that such crusts formed during relatively low-wind, low-humidity, clear-sky periods with intense daytime sunshine. After formation, such glazed surfaces typically developed cracks in a polygonal pattern likely from thermal contraction at night. Cracking was commonest when several clear days occurred in succession and was generally followed by surface hoar growth; vapor escaping through the cracks during sunny days may have contributed to the high humidity that favored nighttime formation of surface hoar. Temperature and radiation observations show that daytime solar heating often warmed the near-surface snow above the air temperature, contributing to upward mass transfer, favoring crust formation from below, and then surface hoar formation. A simple surface energy calculation supports this observation. Subsequent examination of the WDC06A deep ice core revealed that crusts are preserved through the bubbly ice, and some occur in snow accumulated during winters, although not as commonly as in summertime deposits. Although no one has been on site to observe crust formation during winter, it may be favored by greater wintertime wind packing from stronger peak winds, high temperatures and steep temperature gradients from rapid midwinter warmings reaching as high as -15 °C, and perhaps longer intervals of surface stability. Time variations in crust occurrence in the core may provide paleoclimatic information, although additional studies are required. Discontinuity and cracking of crusts likely explain why crusts do not produce significant anomalies in other paleoclimatic records.

Marginal sea surface temperature variation as a pre-cursor of heat waves over the Korean Peninsula

NASA Astrophysics Data System (ADS)

Ham, Yoo-Geun; Na, Hye-Yun

2017-11-01

This study examines the role of the marginal sea surface temperature (SST) on heat waves over Korea. It is found that sea surface warming in the south sea of Korea/Japan (122-138°E, 24- 33°N) causes heat waves after about a week. Due to the frictional force, the positive geopotential height anomalies associated with the south sea warming induce divergent flows over the boundary layer. This divergent flow induces the southerly in Korea, which leads to a positive temperature advection. On the other hand, over the freeatmosphere, the geostrophic wind around high-pressure anomalies flows in a westerly direction over Korea during the south sea warming, which is not effective in temperature advection. Therefore, the positive temperature advection in Korea due to the south sea warming decreases with height. This reduces the vertical potential temperature gradient, which indicates a negative potential vorticity (PV) tendency over Korea. Therefore, the high-pressure anomaly over the south sea of Korea is propagated northward, which results in heat waves due to more incoming solar radiation.

Trichodesmium blooms and warm-core ocean surface features in the Arabian Sea and the Bay of Bengal.

PubMed

Jyothibabu, R; Karnan, C; Jagadeesan, L; Arunpandi, N; Pandiarajan, R S; Muraleedharan, K R; Balachandran, K K

2017-08-15

Trichodesmium is a bloom-forming, diazotrophic, non-heterocystous cyanobacteria widely distributed in the warmer oceans, and their bloom is considered a 'biological indication' of stratification and nitrogen limitation in the ocean surface layer. In the first part of this paper, based on the retrospective analyses of the ocean surface mesoscale features associated with 59 Trichodesmium bloom incidences recorded in the past, 32 from the Arabian Sea and the Bay of Bengal, and 27 from the rest of the world, we have showed that warm-core features have an inducing effect on bloom formation. In the second part, we have considered the environmental preferences of Trichodesmium bloom based on laboratory and field studies across the globe, and proposed a view about how warm-core features could provide an inducing pre-requisite condition for the bloom formation in the Arabian Sea and the Bay of Bengal. Proposed that the subsurface waters of warm-core features maintain more likely chances for the conducive nutrient and light conditions required for the triggering of the blooms. Copyright © 2017 Elsevier Ltd. All rights reserved.

Global Surface Temperature Anomalies and Attribution

NASA Astrophysics Data System (ADS)

Pietrafesa, L. J.

2017-12-01

We study Non-Stationary, Non-Linear time series of global surface temperatures from 1850 to 2016, and via an empirical, mathematical methodology, we reveal the buried, internal modes of variability of planetary temperatures over the past 167 years, and find periods of cooling and warming, both in the ocean and the atmosphere over land, with multiple modes of variability; seasonal, annual, inter-annual, multi-year, decadal, multi-decadal, centennial and overall warming trends in the ocean, atmosphere and the combination therein. The oceanic rate of warming is less than two thirds of that of the atmosphere. While our findings on overall trends of fossil fuel burning and planetary temperatures are only visually correlative, by employing a mathematical methodology well known in ergonomics, this study causally links the upward rise in planetary surface temperature from the latter part of the 19th Century and into the 21st Century, to the contemporaneous upward rise in fossil fuel burning and suggests that if present fossil fuel burning is not curtailed there will be continued warming of the planet in the future.

Observed Thermal Impacts of Wind Farms Over Northern Illinois.

PubMed

Slawsky, Lauren M; Zhou, Liming; Baidya Roy, Somnath; Xia, Geng; Vuille, Mathias; Harris, Ronald A

2015-06-25

This paper assesses impacts of three wind farms in northern Illinois using land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Terra and Aqua satellites for the period 2003-2013. Changes in LST between two periods (before and after construction of the wind turbines) and between wind farm pixels and nearby non-wind-farm pixels are quantified. An areal mean increase in LST by 0.18-0.39 °C is observed at nighttime over the wind farms, with the geographic distribution of this warming effect generally spatially coupled with the layout of the wind turbines (referred to as the spatial coupling), while there is no apparent impact on daytime LST. The nighttime LST warming effect varies with seasons, with the strongest warming in winter months of December-February, and the tightest spatial coupling in summer months of June-August. Analysis of seasonal variations in wind speed and direction from weather balloon sounding data and Automated Surface Observing System hourly observations from nearby stations suggest stronger winds correspond to seasons with greater warming and larger downwind impacts. The early morning soundings in Illinois are representative of the nighttime boundary layer and exhibit strong temperature inversions across all seasons. The strong and relatively shallow inversion in summer leaves warm air readily available to be mixed down and spatially well coupled with the turbine. Although the warming effect is strongest in winter, the spatial coupling is more erratic and spread out than in summer. These results suggest that the observed warming signal at nighttime is likely due to the net downward transport of heat from warmer air aloft to the surface, caused by the turbulent mixing in the wakes of the spinning turbine rotor blades.

Observed Thermal Impacts of Wind Farms Over Northern Illinois

PubMed Central

Slawsky, Lauren M.; Zhou, Liming; Baidya Roy, Somnath; Xia, Geng; Vuille, Mathias; Harris, Ronald A.

2015-01-01

This paper assesses impacts of three wind farms in northern Illinois using land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Terra and Aqua satellites for the period 2003–2013. Changes in LST between two periods (before and after construction of the wind turbines) and between wind farm pixels and nearby non-wind-farm pixels are quantified. An areal mean increase in LST by 0.18–0.39 °C is observed at nighttime over the wind farms, with the geographic distribution of this warming effect generally spatially coupled with the layout of the wind turbines (referred to as the spatial coupling), while there is no apparent impact on daytime LST. The nighttime LST warming effect varies with seasons, with the strongest warming in winter months of December-February, and the tightest spatial coupling in summer months of June-August. Analysis of seasonal variations in wind speed and direction from weather balloon sounding data and Automated Surface Observing System hourly observations from nearby stations suggest stronger winds correspond to seasons with greater warming and larger downwind impacts. The early morning soundings in Illinois are representative of the nighttime boundary layer and exhibit strong temperature inversions across all seasons. The strong and relatively shallow inversion in summer leaves warm air readily available to be mixed down and spatially well coupled with the turbine. Although the warming effect is strongest in winter, the spatial coupling is more erratic and spread out than in summer. These results suggest that the observed warming signal at nighttime is likely due to the net downward transport of heat from warmer air aloft to the surface, caused by the turbulent mixing in the wakes of the spinning turbine rotor blades. PMID:26121613

Ocean Warming, More than Acidification, Reduces Shell Strength in a Commercial Shellfish Species during Food Limitation

PubMed Central

Mackenzie, Clara L.; Ormondroyd, Graham A.; Curling, Simon F.; Ball, Richard J.; Whiteley, Nia M.; Malham, Shelagh K.

2014-01-01

Ocean surface pH levels are predicted to fall by 0.3–0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2–4°C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH –0.4 pH units) and warming (ambient temperature +4°C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4–6 h day−1). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO3 saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited. PMID:24489785

Ocean warming, more than acidification, reduces shell strength in a commercial shellfish species during food limitation.

PubMed

Mackenzie, Clara L; Ormondroyd, Graham A; Curling, Simon F; Ball, Richard J; Whiteley, Nia M; Malham, Shelagh K

2014-01-01

Ocean surface pH levels are predicted to fall by 0.3-0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2-4 °C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH -0.4 pH units) and warming (ambient temperature +4 °C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4-6 h day(-1)). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO3 saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited.

Global warming related transient albedo feedback in the Arctic and its relation to the seasonality of sea ice

NASA Astrophysics Data System (ADS)

Andry, Olivier; Bintanja, Richard; Hazeleger, Wilco

2015-04-01

The Arctic is warming two to three times faster than the global average. Arctic sea ice cover is very sensitive to this warming and has reached historic minima in late summer in recent years (i.e. 2007, 2012). Considering that the Arctic Ocean is mainly ice-covered and that the albedo of sea ice is very high compared to that of open water, the change in sea ice cover is very likely to have a strong impact on the local surface albedo feedback. Here we quantify the temporal changes in surface albedo feedback in response to global warming. Usually feedbacks are evaluated as being representative and constant for long time periods, but we show here that the strength of climate feedbacks in fact varies strongly with time. For instance, time series of the amplitude of the surface albedo feedback, derived from future climate simulations (CIMP5, RCP8.5 up to year 2300) using a kernel method, peaks around the year 2100. This maximum is likely caused by an increased seasonality in sea-ice cover that is inherently associated with sea ice retreat. We demonstrate that the Arctic average surface albedo has a strong seasonal signature with a maximum in spring and a minimum in late summer/autumn. In winter when incoming solar radiation is minimal the surface albedo doesn't have an important effect on the energy balance of the climate system. The annual mean surface albedo is thus determined by the seasonality of both downwelling shortwave radiation and sea ice cover. As sea ice cover reduces the seasonal signature is modified, the transient part from maximum sea ice cover to its minimum is shortened and sharpened. The sea ice cover is reduced when downwelling shortwave radiation is maximum and thus the annual surface albedo is drastically smaller. Consequently the change in annual surface albedo with time will become larger and so will the surface albedo feedback. We conclude that a stronger seasonality in sea ice leads to a stronger surface albedo feedback, which accelerates melting of sea ice. Hence, the change in seasonality and the associated change in feedback strength is an integral part of the positive surface albedo feedback leading to Arctic amplification and diminishing sea ice cover in the next century when global climate warms.

Investigation of warm-mix asphalt for Iowa roadways.

DOT National Transportation Integrated Search

2013-09-01

Phase II of this study further evaluated the performance of plant-produced warm-mix asphalt (WMA) mixes by conducting : additional mixture performance tests at a broader range of temperatures, adding additional pavements to the study, comparing : vir...

Warm Rivers Play Role in Arctic Sea Ice Melt

NASA Image and Video Library

2014-03-05

Beaufort Sea surface temperatures where Canada Mackenzie River discharges into the Arctic Ocean, measured by NASA MODIS instrument; warm river waters had broken through a shoreline sea ice barrier to enhance sea ice melt.

Indian Ocean warming during 1958-2004 simulated by a climate system model and its mechanism

NASA Astrophysics Data System (ADS)

Dong, Lu; Zhou, Tianjun; Wu, Bo

2014-01-01

The mechanism responsible for Indian Ocean Sea surface temperature (SST) basin-wide warming trend during 1958-2004 is studied based on both observational data analysis and numerical experiments with a climate system model FGOALS-gl. To quantitatively estimate the relative contributions of external forcing (anthropogenic and natural forcing) and internal variability, three sets of numerical experiments are conducted, viz. an all forcing run forced by both anthropogenic forcing (greenhouse gases and sulfate aerosols) and natural forcing (solar constant and volcanic aerosols), a natural forcing run driven by only natural forcing, and a pre-industrial control run. The model results are compared to the observations. The results show that the observed warming trend during 1958-2004 (0.5 K (47-year)-1) is largely attributed to the external forcing (more than 90 % of the total trend), while the residual is attributed to the internal variability. Model results indicate that the anthropogenic forcing accounts for approximately 98.8 % contribution of the external forcing trend. Heat budget analysis shows that the surface latent heat flux due to atmosphere and surface longwave radiation, which are mainly associated with anthropogenic forcing, are in favor of the basin-wide warming trend. The basin-wide warming is not spatially uniform, but with an equatorial IOD-like pattern in climate model. The atmospheric processes, oceanic processes and climatological latent heat flux together form an equatorial IOD-like warming pattern, and the oceanic process is the most important in forming the zonal dipole pattern. Both the anthropogenic forcing and natural forcing result in easterly wind anomalies over the equator, which reduce the wind speed, thereby lead to less evaporation and warmer SST in the equatorial western basin. Based on Bjerknes feedback, the easterly wind anomalies uplift the thermocline, which is unfavorable to SST warming in the eastern basin, and contribute to SST warming via deeper thermocline in the western basin. The easterly anomalies also drive westward anomalous equatorial currents, against the eastward climatology currents, which is in favor of the SST warming in the western basin via anomalous warm advection. Therefore, both the atmospheric and oceanic processes are in favor of the IOD-like warming pattern formation over the equator.

Greenhouse warming, decadal variability, or El Nino? An attempt to understand the anomalous 1990s

DOE Office of Scientific and Technical Information (OSTI.GOV)

Latif, M.; Eckert, C.; Kleeman, R.

The dominant variability modes in the Tropics are investigated and contrasted with the anomalous situation observed during the last few years. The prime quantity analyzed is anomalous sea surface temperature (SST) in the region 30{degrees}S-60{degrees}N. Additionally, observed tropical surface wind stress fields were investigated. Further tropical atmospheric information was derived from a multidecadal run with an atmospheric general circulation model that was forced by the same SSTs. The tropical SST variability can be characterized by three modes: an interannual mode [the El Nino-Southern Oscillation (ENSO)], a decadal mode, and a trend or unresolved ultra-low-frequency variability. 48 refs., 20 figs.

Temperature response surfaces for mortality risk of tree species with future drought

DOE PAGES

Adams, Henry D.; Barron-Gafford, Greg A.; Minor, Rebecca L.; ...

2017-11-17

Widespread, high levels of tree mortality, termed forest die-off, associated with drought and rising temperatures, are disrupting forests worldwide. Drought will likely become more frequent with climate change, but even without more frequent drought, higher temperatures can exacerbate tree water stress. The temperature sensitivity of drought-induced mortality of tree species has been evaluated experimentally for only single-step changes in temperature (ambient compared to ambient + increase) rather than as a response surface (multiple levels of temperature increase), which constrains our ability to relate changes in the driver with the biological response. Here we show that time-to-mortality during drought for seedlingsmore » of two western United States tree species, Pinus edulis (Engelm.) and Pinus ponderosa (Douglas ex C. Lawson), declined in continuous proportion with increasing temperature spanning a 7.7 °C increase. Although P. edulis outlived P. ponderosa at all temperatures, both species had similar relative declines in time-to-mortality as temperature increased (5.2% per °C for P. edulis; 5.8% per °C for P. ponderosa). When combined with the non-linear frequency distribution of drought duration—many more short droughts than long droughts—these findings point to a progressive increase in mortality events with global change due to warming alone and independent of additional changes in future drought frequency distributions. As such, dire future forest recruitment patterns are projected assuming the calculated 7–9 seedling mortality events per species by 2100 under business-as-usual warming occur, congruent with additional vulnerability predicted for adult trees from stressors like pathogens and pests. Our progressive projection for increased mortality events was driven primarily by the non-linear shape of the drought duration frequency distribution, a common climate feature of drought-affected regions. These results illustrate profound benefits for reducing emissions of carbon to the atmosphere from anthropogenic sources and slowing warming as rapidly as possible to maximize forest persistence.« less

Temperature response surfaces for mortality risk of tree species with future drought

NASA Astrophysics Data System (ADS)

Adams, Henry D.; Barron-Gafford, Greg A.; Minor, Rebecca L.; Gardea, Alfonso A.; Bentley, Lisa Patrick; Law, Darin J.; Breshears, David D.; McDowell, Nate G.; Huxman, Travis E.

2017-11-01

Widespread, high levels of tree mortality, termed forest die-off, associated with drought and rising temperatures, are disrupting forests worldwide. Drought will likely become more frequent with climate change, but even without more frequent drought, higher temperatures can exacerbate tree water stress. The temperature sensitivity of drought-induced mortality of tree species has been evaluated experimentally for only single-step changes in temperature (ambient compared to ambient + increase) rather than as a response surface (multiple levels of temperature increase), which constrains our ability to relate changes in the driver with the biological response. Here we show that time-to-mortality during drought for seedlings of two western United States tree species, Pinus edulis (Engelm.) and Pinus ponderosa (Douglas ex C. Lawson), declined in continuous proportion with increasing temperature spanning a 7.7 °C increase. Although P. edulis outlived P. ponderosa at all temperatures, both species had similar relative declines in time-to-mortality as temperature increased (5.2% per °C for P. edulis; 5.8% per °C for P. ponderosa). When combined with the non-linear frequency distribution of drought duration—many more short droughts than long droughts—these findings point to a progressive increase in mortality events with global change due to warming alone and independent of additional changes in future drought frequency distributions. As such, dire future forest recruitment patterns are projected assuming the calculated 7-9 seedling mortality events per species by 2100 under business-as-usual warming occur, congruent with additional vulnerability predicted for adult trees from stressors like pathogens and pests. Our progressive projection for increased mortality events was driven primarily by the non-linear shape of the drought duration frequency distribution, a common climate feature of drought-affected regions. These results illustrate profound benefits for reducing emissions of carbon to the atmosphere from anthropogenic sources and slowing warming as rapidly as possible to maximize forest persistence.

Temperature response surfaces for mortality risk of tree species with future drought

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Henry D.; Barron-Gafford, Greg A.; Minor, Rebecca L.

Widespread, high levels of tree mortality, termed forest die-off, associated with drought and rising temperatures, are disrupting forests worldwide. Drought will likely become more frequent with climate change, but even without more frequent drought, higher temperatures can exacerbate tree water stress. The temperature sensitivity of drought-induced mortality of tree species has been evaluated experimentally for only single-step changes in temperature (ambient compared to ambient + increase) rather than as a response surface (multiple levels of temperature increase), which constrains our ability to relate changes in the driver with the biological response. Here we show that time-to-mortality during drought for seedlingsmore » of two western United States tree species, Pinus edulis (Engelm.) and Pinus ponderosa (Douglas ex C. Lawson), declined in continuous proportion with increasing temperature spanning a 7.7 °C increase. Although P. edulis outlived P . ponderosa at all temperatures, both species had similar relative declines in time-to-mortality as temperature increased (5.2% per °C for P. edulis; 5.8% per °C for P. ponderosa). When combined with the non-linear frequency distribution of drought duration—many more short droughts than long droughts—these findings point to a progressive increase in mortality events with global change due to warming alone and independent of additional changes in future drought frequency distributions. As such, dire future forest recruitment patterns are projected assuming the calculated 7-9 seedling mortality events per species by 2100 under business-as-usual warming occurs, congruent with additional vulnerability predicted for adult trees from stressors like pathogens and pests. Our progressive projection for increased mortality events was driven primarily by the non-linear shape of the drought duration frequency distribution, a common climate feature of drought-affected regions. These results illustrate profound benefits for reducing emissions of carbon to the atmosphere from anthropogenic sources and slowing warming as rapidly as possible to maximize forest persistence.« less

Temperature response surfaces for mortality risk of tree species with future drought

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Henry D.; Barron-Gafford, Greg A.; Minor, Rebecca L.

Widespread, high levels of tree mortality, termed forest die-off, associated with drought and rising temperatures, are disrupting forests worldwide. Drought will likely become more frequent with climate change, but even without more frequent drought, higher temperatures can exacerbate tree water stress. The temperature sensitivity of drought-induced mortality of tree species has been evaluated experimentally for only single-step changes in temperature (ambient compared to ambient + increase) rather than as a response surface (multiple levels of temperature increase), which constrains our ability to relate changes in the driver with the biological response. Here we show that time-to-mortality during drought for seedlingsmore » of two western United States tree species, Pinus edulis (Engelm.) and Pinus ponderosa (Douglas ex C. Lawson), declined in continuous proportion with increasing temperature spanning a 7.7 °C increase. Although P. edulis outlived P. ponderosa at all temperatures, both species had similar relative declines in time-to-mortality as temperature increased (5.2% per °C for P. edulis; 5.8% per °C for P. ponderosa). When combined with the non-linear frequency distribution of drought duration—many more short droughts than long droughts—these findings point to a progressive increase in mortality events with global change due to warming alone and independent of additional changes in future drought frequency distributions. As such, dire future forest recruitment patterns are projected assuming the calculated 7–9 seedling mortality events per species by 2100 under business-as-usual warming occur, congruent with additional vulnerability predicted for adult trees from stressors like pathogens and pests. Our progressive projection for increased mortality events was driven primarily by the non-linear shape of the drought duration frequency distribution, a common climate feature of drought-affected regions. These results illustrate profound benefits for reducing emissions of carbon to the atmosphere from anthropogenic sources and slowing warming as rapidly as possible to maximize forest persistence.« less

Feedback attribution of the land-sea warming contrast in a global warming simulation of the NCAR CCSM4

DOE PAGES

Sejas, Sergio A.; Albert, Oriene S.; Cai, Ming; ...

2014-12-02

One of the salient features in both observations and climate simulations is a stronger land warming than sea. This paper provides a quantitative understanding of the main processes that contribute to the land-sea warming asymmetry in a global warming simulation of the NCAR CCSM4. The CO 2 forcing alone warms the surface nearly the same for both land and sea, suggesting that feedbacks are responsible for the warming contrast. Our analysis on one hand confirms that the principal contributor to the above-unity land-to-sea warming ratio is the evaporation feedback; on the other hand the results indicate that the sensible heatmore » flux feedback has the largest land-sea warming difference that favors a greater ocean than land warming. Furthermore, the results uniquely highlight the importance of other feedbacks in establishing the above-unity land-to-sea warming ratio. Particularly, the SW cloud feedback and the ocean heat storage in the transient response are key contributors to the greater warming over land than sea.« less

Feedback attribution of the land-sea warming contrast in a global warming simulation of the NCAR CCSM4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sejas, Sergio A.; Albert, Oriene S.; Cai, Ming

One of the salient features in both observations and climate simulations is a stronger land warming than sea. This paper provides a quantitative understanding of the main processes that contribute to the land-sea warming asymmetry in a global warming simulation of the NCAR CCSM4. The CO 2 forcing alone warms the surface nearly the same for both land and sea, suggesting that feedbacks are responsible for the warming contrast. Our analysis on one hand confirms that the principal contributor to the above-unity land-to-sea warming ratio is the evaporation feedback; on the other hand the results indicate that the sensible heatmore » flux feedback has the largest land-sea warming difference that favors a greater ocean than land warming. Furthermore, the results uniquely highlight the importance of other feedbacks in establishing the above-unity land-to-sea warming ratio. Particularly, the SW cloud feedback and the ocean heat storage in the transient response are key contributors to the greater warming over land than sea.« less

Locust displacing winds in eastern Australia reassessed with observations from an insect monitoring radar

NASA Astrophysics Data System (ADS)

Hao, Zhenhua; Drake, V. Alistair; Sidhu, Leesa; Taylor, John R.

2017-12-01

Based on previous investigations, adult Australian plague locusts are believed to migrate on warm nights (with evening temperatures >25 °C), provided daytime flight is suppressed by surface winds greater than the locusts' flight speed, which has been shown to be 3.1 m s-1. Moreover, adult locusts are believed to undertake briefer `dispersal' flights on nights with evening temperature >20 °C. To reassess the utility of these conditions for forecasting locust flight, contingency tests were conducted comparing the nights selected on these bases (predicted nights) for the months of November, January, and March and the nights when locust migration were detected with an insect monitoring radar (actual nights) over a 7-year period. In addition, the wind direction distributions and mean wind directions on all predicted nights and actual nights were compared. Observations at around 395 m above ground level (AGL), the height at which radar observations have shown that the greatest number of locusts fly, were used to determine the actual nights. Tests and comparisons were also made for a second height, 990 m AGL, as this was used in the previous investigation. Our analysis shows that the proposed criteria are successful from predicting migratory flight only in March, when the surface temperature is effective as a predicting factor. Surface wind speed has no predicting power. It is suggested that a strong daytime surface wind speed requirement should not be considered and other meteorological variables need to be added to the requirement of a warm surface temperature around dusk for the predictions to have much utility.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donner, S.D.; Knutson, T.R.; Oppenheimer, M.

Episodes of mass coral bleaching around the world in recent decades have been attributed to periods of anomalously warm ocean temperatures. In 2005, the sea surface temperature (SST) anomaly in the tropical North Atlantic that may have contributed to the strong hurricane season caused widespread coral bleaching in the Eastern Caribbean. Here, the authors use two global climate models to evaluate the contribution of natural climate variability and anthropogenic forcing to the thermal stress that caused the 2005 coral bleaching event. Historical temperature data and simulations for the 1870-2000 period show that the observed warming in the region is unlikelymore » to be due to unforced climate variability alone. Simulation of background climate variability suggests that anthropogenic warming may have increased the probability of occurrence of significant thermal stress events for corals in this region by an order of magnitude. Under scenarios of future greenhouse gas emissions, mass coral bleaching in the Eastern Caribbean may become a biannual event in 20-30 years. However, if corals and their symbionts can adapt by 1-1.5{sup o}C, such mass bleaching events may not begin to recur at potentially harmful intervals until the latter half of the century. The delay could enable more time to alter the path of greenhouse gas emissions, although long-term 'committed warming' even after stabilization of atmospheric CO{sub 2} levels may still represent an additional long-term threat to corals.« less

Radionuclides in ornithogenic sediments as evidence for recent warming in the Ross Sea region, Antarctica.

PubMed

Nie, Yaguang; Xu, Liqiang; Liu, Xiaodong; Emslie, Steven D

2016-07-01

Radionuclides including (210)Pb, (226)Ra and (137)Cs were analyzed in eight ornithogenic sediment profiles from McMurdo Sound, Ross Sea region, East Antarctica. Equilibration between (210)Pb and (226)Ra were reached in all eight profiles, enabling the determination of chronology within the past two centuries through the Constant Rate of Supply (CRS) model. Calculated fluxes of both (210)Pb and (137)Cs varied drastically among four of the profiles (MB4, MB6, CC and CL2), probably due to differences in their sedimentary environments. In addition, we found the flux data exhibiting a clear decreasing gradient in accordance with their average deposition rate, which was in turn related to the specific location of the profiles. We believe this phenomenon may correspond to global warming of the last century, since warming-induced surface runoff would bring more inflow water and detritus to the coring sites, thus enhancing the difference among the profiles. To verify this hypothesis, the deposition rate against age of the sediments was calculated based on their determined chronology, which showed ascending trends in all four profiles. The significant increase in deposition rates over the last century is probably attributable to recent warming, implying a potential utilization of radionuclides as environmental indicators in this region. Copyright © 2016. Published by Elsevier B.V.

Hiatus-like decades in the absence of equatorial Pacific cooling and accelerated global ocean heat uptake

NASA Astrophysics Data System (ADS)

von Känel, Lukas; Frölicher, Thomas L.; Gruber, Nicolas

2017-08-01

A surface cooling pattern in the equatorial Pacific associated with a negative phase of the Interdecadal Pacific Oscillation is the leading hypothesis to explain the smaller rate of global warming during 1998-2012, with these cooler than normal conditions thought to have accelerated the oceanic heat uptake. Here using a 30-member ensemble simulation of a global Earth system model, we show that in 10% of all simulated decades with a global cooling trend, the eastern equatorial Pacific actually warms. This implies that there is a 1 in 10 chance that decadal hiatus periods may occur without the equatorial Pacific being the dominant pacemaker. In addition, the global ocean heat uptake tends to slow down during hiatus decades implying a fundamentally different global climate feedback factor on decadal time scales than on centennial time scales and calling for caution inferring climate sensitivity from decadal-scale variability.

Impact of decadal cloud variations on the Earth’s energy budget

DOE PAGES

Zhou, Chen; Zelinka, Mark D.; Klein, Stephen A.

2016-10-31

Feedbacks of clouds on climate change strongly influence the magnitude of global warming. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback. We present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. Here, we find that cloud anomalies associated with these patterns significantly modify the Earth’s energy budget. Specifically, the decadal cloud feedback betweenmore » the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. Our results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and o er a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low.« less

Impact of decadal cloud variations on the Earth’s energy budget

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Chen; Zelinka, Mark D.; Klein, Stephen A.

Feedbacks of clouds on climate change strongly influence the magnitude of global warming. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback. We present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. Here, we find that cloud anomalies associated with these patterns significantly modify the Earth’s energy budget. Specifically, the decadal cloud feedback betweenmore » the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. Our results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and o er a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low.« less

Impact of decadal cloud variations on the Earth's energy budget

NASA Astrophysics Data System (ADS)

Zhou, Chen; Zelinka, Mark D.; Klein, Stephen A.

2016-12-01

Feedbacks of clouds on climate change strongly influence the magnitude of global warming. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback. Here we present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. We find that cloud anomalies associated with these patterns significantly modify the Earth's energy budget. Specifically, the decadal cloud feedback between the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. These results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and offer a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low.

Understanding Decreases in Land Relative Humidity with Global Warming: Conceptual Model and GCM Simulations

NASA Astrophysics Data System (ADS)

Byrne, Michael P.; O'Gorman, Paul A.

2016-12-01

Climate models simulate a strong land-ocean contrast in the response of near-surface relative humidity to global warming: relative humidity tends to increase slightly over oceans but decrease substantially over land. Surface energy balance arguments have been used to understand the response over ocean but are difficult to apply over more complex land surfaces. Here, a conceptual box model is introduced, involving moisture transport between the land and ocean boundary layers and evapotranspiration, to investigate the decreases in land relative humidity as the climate warms. The box model is applied to idealized and full-complexity (CMIP5) general circulation model simulations, and it is found to capture many of the features of the simulated changes in land relative humidity. The box model suggests there is a strong link between fractional changes in specific humidity over land and ocean, and the greater warming over land than ocean then implies a decrease in land relative humidity. Evapotranspiration is of secondary importance for the increase in specific humidity over land, but it matters more for the decrease in relative humidity. Further analysis shows there is a strong feedback between changes in surface-air temperature and relative humidity, and this can amplify the influence on relative humidity of factors such as stomatal conductance and soil moisture.

Detecting Global Hydrological Cycle Intensification in Sea Surface Salinity

NASA Astrophysics Data System (ADS)

Poague, J.; Stine, A.

2016-12-01

Global warming is expected to intensify the global hydrological cycle, but significant regional differences exist in the predicted response. The proposed zonal mean thermodynamic response is enhanced horizontal moisture transport associated with increased saturation vapor pressure, which in turn drives additional net precipitation in the tropics and at high latitudes and additional net evaporation in the subtropics. Sea surface salinity (SSS) anomalies are forced from above by changes in evaporation minus precipitation (E-P) and thus will respond to changes in the global hydrological cycle, opening the possibility of using historical SSS anomalies to diagnose the response of the hydrological cycle to warming. We estimate zonal mean SSS trends in the Atlantic and Pacific ocean basins from 1955-2015 to test whether historical changes in the global hydrological cycle are consistent with a primarily thermodynamic response. Motivated by this observation, we calculate the sensitivity of basin zonal-mean SSS anomalies to sea surface temperature (SST) forcing as a function of timescale to diagnose and estimate the signal-to-noise ratio of the purely thermodynamic signal as a function of timescale. High-frequency variability in SSS anomalies is likely to be influenced by variability in atmospheric circulation, complicating the attribution of the link between basin zonal-mean SSS anomalies and global SST anomalies. We therefore estimate the basin zonal mean SSS anomaly response to the major modes of large-scale dynamic variability. We find a strong correlation between detrended zonal-mean SSS anomalies and the Pacific-North American index (R=0.71,P<0.01) in the Pacific Ocean. We interpret the relationship between zonal mean SSS anomalies and temperature in terms of the relative contribution of thermodynamic and dynamic processes.

Asynchronous marine-terrestrial signals of the last deglacial warming in East Asia associated with low- and high-latitude climate changes.

PubMed

Xu, Deke; Lu, Houyuan; Wu, Naiqin; Liu, Zhenxia; Li, Tiegang; Shen, Caiming; Wang, Luo

2013-06-11

A high-resolution multiproxy record, including pollen, foraminifera, and alkenone paleothermometry, obtained from a single core (DG9603) from the Okinawa Trough, East China Sea (ECS), provided unambiguous evidence for asynchronous climate change between the land and ocean over the past 40 ka. On land, the deglacial stage was characterized by rapid warming, as reflected by paleovegetation, and it began ca. 15 kaBP, consistent with the timing of the last deglacial warming in Greenland. However, sea surface temperature estimates from foraminifera and alkenone paleothermometry increased around 20-19 kaBP, as in the Western Pacific Warm Pool (WPWP). Sea surface temperatures in the Okinawa Trough were influenced mainly by heat transport from the tropical western Pacific Ocean by the Kuroshio Current, but the epicontinental vegetation of the ECS was influenced by atmospheric circulation linked to the northern high-latitude climate. Asynchronous terrestrial and marine signals of the last deglacial warming in East Asia were thus clearly related to ocean currents and atmospheric circulation. We argue that (i) early warming seawater of the WPWP, driven by low-latitude insolation and trade winds, moved northward via the Kuroshio Current and triggered marine warming along the ECS around 20-19 kaBP similar to that in the WPWP, and (ii) an almost complete shutdown of the Atlantic Meridional Overturning Circulation ca. 18-15 kaBP was associated with cold Heinrich stadial-1 and delayed terrestrial warming during the last deglacial warming until ca. 15 kaBP at northern high latitudes, and hence in East Asia. Terrestrial deglacial warming therefore lagged behind marine changes by ca. 3-4 ka.

Asynchronous marine-terrestrial signals of the last deglacial warming in East Asia associated with low- and high-latitude climate changes

PubMed Central

Xu, Deke; Lu, Houyuan; Wu, Naiqin; Liu, Zhenxia; Li, Tiegang; Shen, Caiming; Wang, Luo

2013-01-01

A high-resolution multiproxy record, including pollen, foraminifera, and alkenone paleothermometry, obtained from a single core (DG9603) from the Okinawa Trough, East China Sea (ECS), provided unambiguous evidence for asynchronous climate change between the land and ocean over the past 40 ka. On land, the deglacial stage was characterized by rapid warming, as reflected by paleovegetation, and it began ca. 15 kaBP, consistent with the timing of the last deglacial warming in Greenland. However, sea surface temperature estimates from foraminifera and alkenone paleothermometry increased around 20–19 kaBP, as in the Western Pacific Warm Pool (WPWP). Sea surface temperatures in the Okinawa Trough were influenced mainly by heat transport from the tropical western Pacific Ocean by the Kuroshio Current, but the epicontinental vegetation of the ECS was influenced by atmospheric circulation linked to the northern high-latitude climate. Asynchronous terrestrial and marine signals of the last deglacial warming in East Asia were thus clearly related to ocean currents and atmospheric circulation. We argue that (i) early warming seawater of the WPWP, driven by low-latitude insolation and trade winds, moved northward via the Kuroshio Current and triggered marine warming along the ECS around 20–19 kaBP similar to that in the WPWP, and (ii) an almost complete shutdown of the Atlantic Meridional Overturning Circulation ca. 18–15 kaBP was associated with cold Heinrich stadial-1 and delayed terrestrial warming during the last deglacial warming until ca. 15 kaBP at northern high latitudes, and hence in East Asia. Terrestrial deglacial warming therefore lagged behind marine changes by ca. 3–4 ka. PMID:23720306

Coupling physics and biogeochemistry thanks to high-resolution observations of the phytoplankton community structure in the northwestern Mediterranean Sea

NASA Astrophysics Data System (ADS)

Marrec, Pierre; Grégori, Gérald; Doglioli, Andrea M.; Dugenne, Mathilde; Della Penna, Alice; Bhairy, Nagib; Cariou, Thierry; Hélias Nunige, Sandra; Lahbib, Soumaya; Rougier, Gilles; Wagener, Thibaut; Thyssen, Melilotus

2018-03-01

Fine-scale physical structures and ocean dynamics strongly influence and regulate biogeochemical and ecological processes. These processes are particularly challenging to describe and understand because of their ephemeral nature. The OSCAHR (Observing Submesoscale Coupling At High Resolution) campaign was conducted in fall 2015 in which a fine-scale structure (1-10 km/1-10 days) in the northwestern Mediterranean Ligurian subbasin was pre-identified using both satellite and numerical modeling data. Along the ship track, various variables were measured at the surface (temperature, salinity, chlorophyll a and nutrient concentrations) with ADCP current velocity. We also deployed a new model of the CytoSense automated flow cytometer (AFCM) optimized for small and dim cells, for near real-time characterization of the surface phytoplankton community structure of surface waters with a spatial resolution of a few kilometers and an hourly temporal resolution. For the first time with this optimized version of the AFCM, we were able to fully resolve Prochlorococcus picocyanobacteria in addition to the easily distinguishable Synechococcus. The vertical physical dynamics and biogeochemical properties of the studied area were investigated by continuous high-resolution CTD profiles thanks to a moving vessel profiler (MVP) during the vessel underway associated with a high-resolution pumping system deployed during fixed stations allowing sampling of the water column at a fine resolution (below 1 m). The observed fine-scale feature presented a cyclonic structure with a relatively cold core surrounded by warmer waters. Surface waters were totally depleted in nitrate and phosphate. In addition to the doming of the isopycnals by the cyclonic circulation, an intense wind event induced Ekman pumping. The upwelled subsurface cold nutrient-rich water fertilized surface waters and was marked by an increase in Chl a concentration. Prochlorococcus and pico- and nano-eukaryotes were more abundant in cold core waters, while Synechococcus dominated in warm boundary waters. Nanoeukaryotes were the main contributors ( > 50 %) in terms of pigment content (red fluorescence) and biomass. Biological observations based on the mean cell's red fluorescence recorded by AFCM combined with physical properties of surface waters suggest a distinct origin for two warm boundary waters. Finally, the application of a matrix growth population model based on high-frequency AFCM measurements in warm boundary surface waters provides estimates of in situ growth rate and apparent net primary production for Prochlorococcus (μ = 0.21 d-1, NPP = 0.11 mg C m-3 d-1) and Synechococcus (μ = 0.72 d-1, NPP = 2.68 mg C m-3 d-1), which corroborate their opposite surface distribution pattern. The innovative adaptive strategy applied during OSCAHR with a combination of several multidisciplinary and complementary approaches involving high-resolution in situ observations and sampling, remote-sensing and model simulations provided a deeper understanding of the marine biogeochemical dynamics through the first trophic levels.

Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations

NASA Astrophysics Data System (ADS)

Nuijens, Louise; Emanuel, Kerry; Masunaga, Hirohiko; L'Ecuyer, Tristan

2017-11-01

Space-borne observations reveal that 20-40% of marine convective clouds below the freezing level produce rain. In this paper we speculate what the prevalence of warm rain might imply for convection and large-scale circulations over tropical oceans. We present results using a two-column radiative-convective model of hydrostatic, nonlinear flow on a non-rotating sphere, with parameterized convection and radiation, and review ongoing efforts in high-resolution modeling and observations of warm rain. The model experiments investigate the response of convection and circulation to sea surface temperature (SST) gradients between the columns and to changes in a parameter that controls the conversion of cloud condensate to rain. Convection over the cold ocean collapses to a shallow mode with tops near 850 hPa, but a congestus mode with tops near 600 hPa can develop at small SST differences when warm rain formation is more efficient. Here, interactive radiation and the response of the circulation are crucial: along with congestus a deeper moist layer develops, which leads to less low-level radiative cooling, a smaller buoyancy gradient between the columns, and therefore a weaker circulation and less subsidence over the cold ocean. The congestus mode is accompanied with more surface precipitation in the subsiding column and less surface precipitation in the deep convecting column. For the shallow mode over colder oceans, circulations also weaken with more efficient warm rain formation, but only marginally. Here, more warm rain reduces convective tops and the boundary layer depth—similar to Large-Eddy Simulation (LES) studies—which reduces the integrated buoyancy gradient. Elucidating the impact of warm rain can benefit from large-domain high-resolution simulations and observations. Parameterizations of warm rain may be constrained through collocated cloud and rain profiling from ground, and concurrent changes in convection and rain in subsiding and convecting branches of circulations may be revealed from a collocation of space-borne sensors, including the Global Precipitation Measurement (GPM) and upcoming Aeolus missions.

Strong Dependence of U.S. Summertime Air Quality on the Decadal Variability of Atlantic Sea Surface Temperatures

NASA Astrophysics Data System (ADS)

Shen, Lu; Mickley, Loretta J.; Leibensperger, Eric M.; Li, Mingwei

2017-12-01

We find that summertime air quality in the eastern U.S. displays strong dependence on North Atlantic sea surface temperatures, resulting from large-scale ocean-atmosphere interactions. Using observations, reanalysis data sets, and climate model simulations, we further identify a multidecadal variability in surface air quality driven by the Atlantic Multidecadal Oscillation (AMO). In one-half cycle ( 35 years) of the AMO from cold to warm phase, summertime maximum daily 8 h ozone concentrations increase by 1-4 ppbv and PM2.5 concentrations increase by 0.3-1.0 μg m-3 over much of the east. These air quality changes are related to warmer, drier, and more stagnant weather in the AMO warm phase, together with anomalous circulation patterns at the surface and aloft. If the AMO shifts to the cold phase in future years, it could partly offset the climate penalty on U.S. air quality brought by global warming, an effect which should be considered in long-term air quality planning.

Sensitivity of Stratospheric Geoengineering with Black Carbon to Aerosol Size and Altitude of Injection

NASA Technical Reports Server (NTRS)

Kravitz, Ben; Robock, Alan; Shindell, Drew T.; Miller, Mark A.

2012-01-01

Simulations of stratospheric geoengineering with black carbon (BC) aerosols using a general circulation model with fixed sea surface temperatures show that the climate effects strongly depend on aerosol size and altitude of injection. 1 Tg BC/a injected into the lower stratosphere would cause little surface cooling for large radii but a large amount of surface cooling for small radii and stratospheric warming of over 60 C. With the exception of small particles, increasing the altitude of injection increases surface cooling and stratospheric warming. Stratospheric warming causes global ozone loss by up to 50% in the small radius case. The Antarctic shows less ozone loss due to reduction of polar stratospheric clouds, but strong circumpolar winds would enhance the Arctic ozone hole. Using diesel fuel to produce the aerosols is likely prohibitively expensive and infeasible. Although studying an absorbing aerosol is a useful counterpart to previous studies involving sulfate aerosols, black carbon geoengineering likely carries too many risks to make it a viable option for deployment.

Simple additive simulation overestimates real influence: altered nitrogen and rainfall modulate the effect of warming on soil carbon fluxes.

PubMed

Ni, Xiangyin; Yang, Wanqin; Qi, Zemin; Liao, Shu; Xu, Zhenfeng; Tan, Bo; Wang, Bin; Wu, Qinggui; Fu, Changkun; You, Chengming; Wu, Fuzhong

2017-08-01

Experiments and models have led to a consensus that there is positive feedback between carbon (C) fluxes and climate warming. However, the effect of warming may be altered by regional and global changes in nitrogen (N) and rainfall levels, but the current understanding is limited. Through synthesizing global data on soil C pool, input and loss from experiments simulating N deposition, drought and increased precipitation, we quantified the responses of soil C fluxes and equilibrium to the three single factors and their interactions with warming. We found that warming slightly increased the soil C input and loss by 5% and 9%, respectively, but had no significant effect on the soil C pool. Nitrogen deposition alone increased the soil C input (+20%), but the interaction of warming and N deposition greatly increased the soil C input by 49%. Drought alone decreased the soil C input by 17%, while the interaction of warming and drought decreased the soil C input to a greater extent (-22%). Increased precipitation stimulated the soil C input by 15%, but the interaction of warming and increased precipitation had no significant effect on the soil C input. However, the soil C loss was not significantly affected by any of the interactions, although it was constrained by drought (-18%). These results implied that the positive C fluxes-climate warming feedback was modulated by the changing N and rainfall regimes. Further, we found that the additive effects of [warming × N deposition] and [warming × drought] on the soil C input and of [warming × increased precipitation] on the soil C loss were greater than their interactions, suggesting that simple additive simulation using single-factor manipulations may overestimate the effects on soil C fluxes in the real world. Therefore, we propose that more multifactorial experiments should be considered in studying Earth systems. © 2016 John Wiley & Sons Ltd.

The impacts of intense moisture transport on the deep and marginal sea-ice zones of the Arctic during winter

NASA Astrophysics Data System (ADS)

Woods, Cian; Caballero, Rodrigo

2015-04-01

Over the past few decades observations have shown that the Arctic is warming at a much faster rate than the global average; a phenomenon know as polar amplification. This tendency for the high latitudes to warm at a disproportionate rate compared to the global average is also a robust feature of global climate model simulations and highlights the importance of climate research in this region. The most often cited mechanism explaining polar amplification is the ice-albedo feed-back; a mechanism by which the surface albedo decreases as sea ice retreats in response to a warming climate. This in turn leads to a higher absorption of insolation and the melting of more ice. In recent years the role of the ice-albedo feedback mechanism as the main cause of polar amplification has been brought into question. GCM studies show a slight reduction of the total poleward energy transport in a warming climate; with the dry static component decreasing at a much faster rate than the moist component. This repartitioning of the poleward energy transport has implications for the formation of clouds in the Arctic, which induce a secondary warming by trapping escaping OLR. These cloud processes in the atmosphere can explain at least part of the recent temperature amplification in the Arctic; and indeed even aquaplanet model studies with zero sea-ice reproduce the polar amplification phenomenon. Directionally, the ice-albedo feedback is a "bottom-up" process; inducing warming in the atmosphere from an increasing surface heat source i.e. more open ocean. The opening of more ocean surface is also consistent with the bottom amplified structure of warming in the Arctic. Here we present evidence for a mechanism in the atmosphere that matches with observations, but in fact acts the opposite direction i.e. "top-down", whereby moist air masses from lower latitudes, termed "moisture intrusions", travelling over the sea-ice increase the longwave down radiation and in turn induce a bottom amplified warming at the surface. There are an average of 14 such events that enter the polar cap each winter, driving about 50% of the seasonal variation in surface temperature over the deep Arctic. We show that, over the last 30 years, the marginal ice-zones in the Barents, Labrador and Chukchi Seas have experienced roughly a doubling in the frequency of these intense moisture intrusion events during winter. Interestingly, these are the regions that have experienced the most rapid wintertime ice loss in the Arctic, raising the question: to what extent has the recent Arctic warming been driven by local vs. interannual/remote processes?

Regional difference of the vertical structure of seasonal thermocline and its impact on sea surface temperature in the North Pacific

NASA Astrophysics Data System (ADS)

Yamaguchi, R.; Suga, T.

2016-12-01

Recent observational studies show that, during the warming season, a large amount of heat flux is penetrated through the base of thin mixed layer by vertical eddy diffusion, in addition to penetration of solar radiation [1]. In order to understand this heat penetration process due to vertical eddy diffusivity and its contribution to seasonal variation of sea surface temperature, we investigated the evolution of thermal stratification below the summertime thin mixed layer (i.e. evolution of seasonal thermocline) and its vertical structure in the North Pacific using high vertical resolution temperature profile observed by Argo floats. We quantified the vertical structure of seasonal thermocline as deviations from the linear structure where the vertical gradient of temperature is constant, that is, "shape anomaly". The shape anomaly is variable representing the extent of the bend of temperature profiles. We found that there are larger values of shape anomaly in the region where the seasonal sea surface temperature warming is relatively faster. To understand the regional difference of shape anomalies, we investigated the relationship between time changes in shape anomalies and net surface heat flux and surface kinetic energy flux. From May to July, the analysis indicated that, in a large part of North Pacific, there's a tendency for shape anomalies to develop strongly (weakly) under the conditions of large (small) downward net surface heat flux and small (large) downward surface kinetic energy flux. Since weak (strong) development of shape anomalies means efficient (inefficient) downward heat transport from the surface, these results suggest that the regional difference of the downward heat penetration below mixed layer is explained reasonably well by differences in surface heat forcing and surface wind forcing in a vertical one dimensional framework. [1] Hosoda et al. (2015), J. Oceanogr., 71, 541-556.

A global database of lake surface temperatures collected by in situ and satellite methods from 1985–2009

PubMed Central

Sharma, Sapna; Gray, Derek K; Read, Jordan S; O’Reilly, Catherine M; Schneider, Philipp; Qudrat, Anam; Gries, Corinna; Stefanoff, Samantha; Hampton, Stephanie E; Hook, Simon; Lenters, John D; Livingstone, David M; McIntyre, Peter B; Adrian, Rita; Allan, Mathew G; Anneville, Orlane; Arvola, Lauri; Austin, Jay; Bailey, John; Baron, Jill S; Brookes, Justin; Chen, Yuwei; Daly, Robert; Dokulil, Martin; Dong, Bo; Ewing, Kye; de Eyto, Elvira; Hamilton, David; Havens, Karl; Haydon, Shane; Hetzenauer, Harald; Heneberry, Jocelyne; Hetherington, Amy L; Higgins, Scott N; Hixson, Eric; Izmest’eva, Lyubov R; Jones, Benjamin M; Kangur, Külli; Kasprzak, Peter; Köster, Olivier; Kraemer, Benjamin M; Kumagai, Michio; Kuusisto, Esko; Leshkevich, George; May, Linda; MacIntyre, Sally; Müller-Navarra, Dörthe; Naumenko, Mikhail; Noges, Peeter; Noges, Tiina; Niederhauser, Pius; North, Ryan P; Paterson, Andrew M; Plisnier, Pierre-Denis; Rigosi, Anna; Rimmer, Alon; Rogora, Michela; Rudstam, Lars; Rusak, James A; Salmaso, Nico; Samal, Nihar R; Schindler, Daniel E; Schladow, Geoffrey; Schmidt, Silke R; Schultz, Tracey; Silow, Eugene A; Straile, Dietmar; Teubner, Katrin; Verburg, Piet; Voutilainen, Ari; Watkinson, Andrew; Weyhenmeyer, Gesa A; Williamson, Craig E; Woo, Kara H

2015-01-01

Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues. PMID:25977814

A global database of lake surface temperatures collected by in situ and satellite methods from 1985-2009.

PubMed

Sharma, Sapna; Gray, Derek K; Read, Jordan S; O'Reilly, Catherine M; Schneider, Philipp; Qudrat, Anam; Gries, Corinna; Stefanoff, Samantha; Hampton, Stephanie E; Hook, Simon; Lenters, John D; Livingstone, David M; McIntyre, Peter B; Adrian, Rita; Allan, Mathew G; Anneville, Orlane; Arvola, Lauri; Austin, Jay; Bailey, John; Baron, Jill S; Brookes, Justin; Chen, Yuwei; Daly, Robert; Dokulil, Martin; Dong, Bo; Ewing, Kye; de Eyto, Elvira; Hamilton, David; Havens, Karl; Haydon, Shane; Hetzenauer, Harald; Heneberry, Jocelyne; Hetherington, Amy L; Higgins, Scott N; Hixson, Eric; Izmest'eva, Lyubov R; Jones, Benjamin M; Kangur, Külli; Kasprzak, Peter; Köster, Olivier; Kraemer, Benjamin M; Kumagai, Michio; Kuusisto, Esko; Leshkevich, George; May, Linda; MacIntyre, Sally; Müller-Navarra, Dörthe; Naumenko, Mikhail; Noges, Peeter; Noges, Tiina; Niederhauser, Pius; North, Ryan P; Paterson, Andrew M; Plisnier, Pierre-Denis; Rigosi, Anna; Rimmer, Alon; Rogora, Michela; Rudstam, Lars; Rusak, James A; Salmaso, Nico; Samal, Nihar R; Schindler, Daniel E; Schladow, Geoffrey; Schmidt, Silke R; Schultz, Tracey; Silow, Eugene A; Straile, Dietmar; Teubner, Katrin; Verburg, Piet; Voutilainen, Ari; Watkinson, Andrew; Weyhenmeyer, Gesa A; Williamson, Craig E; Woo, Kara H

2015-01-01

Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985-2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues.

A global database of lake surface temperatures collected by in situ and satellite methods from 1985–2009

USGS Publications Warehouse

Sharma, Sapna; Gray, Derek; Read, Jordan S.; O'Reilly, Catherine; Schneider, Philipp; Qudrat, Anam; Gries, Corinna; Stefanoff, Samantha; Hampton, Stephanie; Hook, Simon; Lenters, John; Livingstone, David M.; McIntyre, Peter B.; Adrian, Rita; Allan, Mathew; Anneville, Orlane; Arvola, Lauri; Austin, Jay; Bailey, John E.; Baron, Jill S.; Brookes, Justin D; Chen, Yuwei; Daly, Robert; Ewing, Kye; de Eyto, Elvira; Dokulil, Martin; Hamilton, David B.; Havens, Karl; Haydon, Shane; Hetzenaeur, Harald; Heneberry, Jocelyn; Hetherington, Amy; Higgins, Scott; Hixson, Eric; Izmest'eva, Lyubov; Jones, Benjamin M.; Kangur, Kulli; Kasprzak, Peter; Kraemer, Benjamin; Kumagai, Michio; Kuusisto, Esko; Leshkevich, George; May, Linda; MacIntyre, Sally; Dörthe Müller-Navarra,; Naumenko, Mikhail; Noges, Peeter; Noges, Tiina; Pius Niederhauser,; North, Ryan P.; Andrew Paterson,; Plisnier, Pierre-Denis; Rigosi, Anna; Rimmer, Alon; Rogora, Michela; Rudstam, Lars G.; Rusak, James A.; Salmaso, Nico; Samal, Nihar R.; Daniel E. Schindler,; Geoffrey Schladow,; Schmidt, Silke R.; Tracey Schultz,; Silow, Eugene A.; Straile, Dietmar; Teubner, Katrin; Verburg, Piet; Voutilainen, Ari; Watkinson, Andrew; Weyhenmeyer, Gesa A.; Craig E. Williamson,; Kara H. Woo,

2015-01-01

Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues.

Observed warming over northern South America has an anthropogenic origin

NASA Astrophysics Data System (ADS)

Barkhordarian, Armineh; von Storch, Hans; Zorita, Eduardo; Loikith, Paul C.; Mechoso, Carlos R.

2017-10-01

We investigate whether the recently observed trends in daily maximum and minimum near-surface air temperature (Tmax and Tmin, respectively) over South America (SA) are consistent with the simulated response of Tmin and Tmax to anthropogenic forcing. Results indicate that the recently observed warming in the dry seasons is well beyond the range of natural (internal) variability. In the wet season the natural modes of variability explain a substantial portion of Tmin and Tmax variability. We demonstrate that the large-scale component of greenhouse gas (GHG) forcing is detectable in dry-seasonal warming. However, none of the global and regional climate change projections reproduce the observed warming of up to 0.6 K/Decade in Tmax in 1983-2012 over northern SA during the austral spring (SON). Thus, besides the global manifestation of GHG forcing, other external drivers have an imprint. Using aerosols-only forcing simulations, our results provide evidence that anthropogenic aerosols also have a detectable influence in SON and that the indirect effect of aerosols on cloud's lifetime is more compatible with the observed record. In addition, there is an increasing trend in the observed incoming solar radiation over northern SA in SON, which is larger than expected from natural (internal) variability alone. We further show that in the dry seasons the spread of projected trends based on the RCP4.5 scenario derived from 30 CMIP5 models encompasses the observed area-averaged trends in Tmin and Tmax. This may imply that the observed excessive warming in the dry seasons serve as an illustration of plausible future expected change in the region.

Combined Effects of Ocean Warming and Acidification on Copepod Abundance, Body Size and Fatty Acid Content.

PubMed

Garzke, Jessica; Hansen, Thomas; Ismar, Stefanie M H; Sommer, Ulrich

2016-01-01

Concerns about increasing atmospheric CO2 concentrations and global warming have initiated studies on the consequences of multiple-stressor interactions on marine organisms and ecosystems. We present a fully-crossed factorial mesocosm study and assess how warming and acidification affect the abundance, body size, and fatty acid composition of copepods as a measure of nutritional quality. The experimental set-up allowed us to determine whether the effects of warming and acidification act additively, synergistically, or antagonistically on the abundance, body size, and fatty acid content of copepods, a major group of lower level consumers in marine food webs. Copepodite (developmental stages 1-5) and nauplii abundance were antagonistically affected by warming and acidification. Higher temperature decreased copepodite and nauplii abundance, while acidification partially compensated for the temperature effect. The abundance of adult copepods was negatively affected by warming. The prosome length of copepods was significantly reduced by warming, and the interaction of warming and CO2 antagonistically affected prosome length. Fatty acid composition was also significantly affected by warming. The content of saturated fatty acids increased, and the ratios of the polyunsaturated essential fatty acids docosahexaenoic- (DHA) and arachidonic acid (ARA) to total fatty acid content increased with higher temperatures. Additionally, here was a significant additive interaction effect of both parameters on arachidonic acid. Our results indicate that in a future ocean scenario, acidification might partially counteract some observed effects of increased temperature on zooplankton, while adding to others. These may be results of a fertilizing effect on phytoplankton as a copepod food source. In summary, copepod populations will be more strongly affected by warming rather than by acidifying oceans, but ocean acidification effects can modify some temperature impacts.

Combined Effects of Ocean Warming and Acidification on Copepod Abundance, Body Size and Fatty Acid Content

PubMed Central

Hansen, Thomas; Ismar, Stefanie M. H.; Sommer, Ulrich

2016-01-01

Concerns about increasing atmospheric CO2 concentrations and global warming have initiated studies on the consequences of multiple-stressor interactions on marine organisms and ecosystems. We present a fully-crossed factorial mesocosm study and assess how warming and acidification affect the abundance, body size, and fatty acid composition of copepods as a measure of nutritional quality. The experimental set-up allowed us to determine whether the effects of warming and acidification act additively, synergistically, or antagonistically on the abundance, body size, and fatty acid content of copepods, a major group of lower level consumers in marine food webs. Copepodite (developmental stages 1–5) and nauplii abundance were antagonistically affected by warming and acidification. Higher temperature decreased copepodite and nauplii abundance, while acidification partially compensated for the temperature effect. The abundance of adult copepods was negatively affected by warming. The prosome length of copepods was significantly reduced by warming, and the interaction of warming and CO2 antagonistically affected prosome length. Fatty acid composition was also significantly affected by warming. The content of saturated fatty acids increased, and the ratios of the polyunsaturated essential fatty acids docosahexaenoic- (DHA) and arachidonic acid (ARA) to total fatty acid content increased with higher temperatures. Additionally, here was a significant additive interaction effect of both parameters on arachidonic acid. Our results indicate that in a future ocean scenario, acidification might partially counteract some observed effects of increased temperature on zooplankton, while adding to others. These may be results of a fertilizing effect on phytoplankton as a copepod food source. In summary, copepod populations will be more strongly affected by warming rather than by acidifying oceans, but ocean acidification effects can modify some temperature impacts. PMID:27224476

Thermal-powered reciprocating pump

NASA Technical Reports Server (NTRS)

Sabelman, E. E.

1972-01-01

Waste heat from radioisotope thermal generators in spacecraft is transported to keep instruments warm by two-cylinder reciprocating pump powered by energy from warm heat exchange fluid. Each cylinder has thermally nonconductive piston, heat exchange coil, and heat sink surface.

Seasonal Flows in Palikir Crater

NASA Image and Video Library

2013-05-15

Seasonal flows on warm Martian slopes may be caused by the flow of salty water on Mars, active today when the surface is warm above the freezing point of the solution. This observation is from NASA Mars Reconnaissance Orbiter.

Middle Pliocene sea surface temperature variability

USGS Publications Warehouse

Dowsett, H.J.; Chandler, M.A.; Cronin, T. M.; Dwyer, Gary S.

2005-01-01

Estimates of sea surface temperature (SST) based upon foraminifer, diatom, and ostracod assemblages from ocean cores reveal a warm phase of the Pliocene between about 3.3 and 3.0 Ma. Pollen records and plant megafossils, although not as well dated, show evidence for a warmer climate at about the same time. Increased greenhouse forcing and altered ocean heat transport are the leading candidates for the underlying cause of Pliocene global warmth. Despite being a period of global warmth, this interval encompasses considerable variability. Two new SST reconstructions are presented that are designed to provide a climatological error bar for warm peak phases of the Pliocene and to document the spatial distribution and magnitude of SST variability within the mid-Pliocene warm period. These data suggest long-term stability of low-latitude SST and document greater variability in regions of maximum warming. Copyright 2005 by the American Geophysical Union.

Climate Impacts From a Removal of Anthropogenic Aerosol Emissions

NASA Astrophysics Data System (ADS)

Samset, B. H.; Sand, M.; Smith, C. J.; Bauer, S. E.; Forster, P. M.; Fuglestvedt, J. S.; Osprey, S.; Schleussner, C.-F.

2018-01-01

Limiting global warming to 1.5 or 2.0°C requires strong mitigation of anthropogenic greenhouse gas (GHG) emissions. Concurrently, emissions of anthropogenic aerosols will decline, due to coemission with GHG, and measures to improve air quality. However, the combined climate effect of GHG and aerosol emissions over the industrial era is poorly constrained. Here we show the climate impacts from removing present-day anthropogenic aerosol emissions and compare them to the impacts from moderate GHG-dominated global warming. Removing aerosols induces a global mean surface heating of 0.5-1.1°C, and precipitation increase of 2.0-4.6%. Extreme weather indices also increase. We find a higher sensitivity of extreme events to aerosol reductions, per degree of surface warming, in particular over the major aerosol emission regions. Under near-term warming, we find that regional climate change will depend strongly on the balance between aerosol and GHG forcing.

Initiation of clement surface conditions on the earliest Earth

PubMed Central

Sleep, N. H.; Zahnle, K.; Neuhoff, P. S.

2001-01-01

In the beginning the surface of the Earth was extremely hot, because the Earth as we know it is the product of a collision between two planets, a collision that also created the Moon. Most of the heat within the very young Earth was lost quickly to space while the surface was still quite hot. As it cooled, the Earth's surface passed monotonically through every temperature regime between silicate vapor to liquid water and perhaps even to ice, eventually reaching an equilibrium with sunlight. Inevitably the surface passed through a time when the temperature was around 100°C at which modern thermophile organisms live. How long this warm epoch lasted depends on how long a thick greenhouse atmosphere can be maintained by heat flow from the Earth's interior, either directly as a supplement to insolation, or indirectly through its influence on the nascent carbonate cycle. In both cases, the duration of the warm epoch would have been controlled by processes within the Earth's interior where buffering by surface conditions played little part. A potentially evolutionarily significant warm period of between 105 and 107 years seems likely, which nonetheless was brief compared to the vast expanse of geological time. PMID:11259665

Initiation of clement surface conditions on the earliest Earth.

PubMed

Sleep, N H; Zahnle, K; Neuhoff, P S

2001-03-27

In the beginning the surface of the Earth was extremely hot, because the Earth as we know it is the product of a collision between two planets, a collision that also created the Moon. Most of the heat within the very young Earth was lost quickly to space while the surface was still quite hot. As it cooled, the Earth's surface passed monotonically through every temperature regime between silicate vapor to liquid water and perhaps even to ice, eventually reaching an equilibrium with sunlight. Inevitably the surface passed through a time when the temperature was around 100 degrees C at which modern thermophile organisms live. How long this warm epoch lasted depends on how long a thick greenhouse atmosphere can be maintained by heat flow from the Earth's interior, either directly as a supplement to insolation, or indirectly through its influence on the nascent carbonate cycle. In both cases, the duration of the warm epoch would have been controlled by processes within the Earth's interior where buffering by surface conditions played little part. A potentially evolutionarily significant warm period of between 10(5) and 10(7) years seems likely, which nonetheless was brief compared to the vast expanse of geological time.

Variability of Coastal and Ocean Water Temperature in the Upper 700 m along the Western Iberian Peninsula from 1975 to 2006

PubMed Central

Santos, Fran; Gómez-Gesteira, Moncho; deCastro, Maite; Álvarez, Inés

2012-01-01

Temperature is observed to have different trends at coastal and ocean locations along the western Iberian Peninsula from 1975 to 2006, which corresponds to the last warming period in the area under study. The analysis was carried out by means of the Simple Ocean Data Assimilation (SODA). Reanalysis data are available at monthly scale with a horizontal resolution of 0.5°×0.5° and a vertical resolution of 40 levels, which allows obtaining information beneath the sea surface. Only the first 21 vertical levels (from 5.0 m to 729.35 m) were considered here, since the most important changes in heat content observed for the world ocean during the last decades, correspond to the upper 700 m. Warming was observed to be considerably higher at ocean locations than at coastal ones. Ocean warming ranged from values on the order of 0.3°C dec−1 near surface to less than 0.1°C dec−1 at 500 m, while coastal warming showed values close to 0.2°C dec−1 near surface, decreasing rapidly below 0.1°C dec−1 for depths on the order of 50 m. The heat content anomaly for the upper 700 m, showed a sharp increase from coast (0.46 Wm−2) to ocean (1.59 Wm−2). The difference between coastal and ocean values was related to the presence of coastal upwelling, which partially inhibits the warming from surface of near shore water. PMID:23226533

Warming-related increases in soil CO2 efflux are explained by increased below-ground carbon flux

Treesearch

Christian P. Giardina; Creighton M. Litton; Susan E. Crow; Gregory P Asner

2014-01-01

The universally observed exponential increase in soil-surface CO2 effux (‘soil respiration’; FS) with increasing temperature has led to speculation that global warming will accelerate soil organic carbon (SOC) decomposition, reduce SOC storage, and drive a positive feedback to future warming. However, interpreting temperature–FS relationships,...

SPRUCE Deep Peat Heating Manipulations: in situ Methods to Characterize the Response of Deep Peat to Warming

NASA Astrophysics Data System (ADS)

Hanson, P. J.; Riggs, J. S.; Barbier, C. N.; Nettles, W. R., IV; Phillips, J. R.; Hook, L.

2014-12-01

Deep soil heating infrastructure was completed in 2014 for a peatland whole-ecosystem warming study that will include air warming starting in 2015 (SPRUCE; http://mnspruce.ornl.gov). In June 2014, we initiated deep soil heating to test the responsiveness of deep peat carbon stocks, microbial communities and biogeochemical cycling processes to heating at 4 warming levels (+2.25, +4.5, +6.75 and +9 °C; 2 replicate plots) compared to fully-constructed control plots (+0 °C; 2 replicate plots). The warming treatments were deployed over eight 113 m2 areas using circular arrays of low-wattage (W) electrical resistance heaters. Perimeter heating was achieved by an exterior circle of 48 100W heaters that apply heat from the surface to a depth of 3 meters. Heating within the study area was accomplished utilizing three zones of 100W "deep only" heaters: an intermediate circle of 12 units, an interior circle of 6 units and one unit placed at the plot center. Heating elements inside the study area apply heat only from -2 to -3 m to keep active heater surfaces away from measured peat volumes. With an average peat depth of 2.5 meters this system was able to warm approximately 113 of the 282 m3 of peat within each target plot. In the absence of the air warming cap, in situ deep peat heating is only effective at sustaining warming in the deep peat layers. Warming levels at depth were achieved over a 25-day (+ 2.25 °C) to a 60-day (+9 °C) period depending on the target treatment temperatures in agreement with a priori energy balance model simulations. Homogeneous temperature distributions between heaters at a given depth interval continued to develop after these targets were reached. Biological and biogeochemical responses to these manipulations are being actively assessed. After one month of transient heating, data for ground-level surface flux of CO2 and CH4 had not shown changes from deep peat heating, but they continue to be tracked and will be summarized in this and related talks.

Differential arthropod responses to warming are altering the structure of Arctic communities

PubMed Central

2018-01-01

The Arctic is experiencing some of the fastest rates of warming on the planet. Although many studies have documented responses to such warming by individual species, the idiosyncratic nature of these findings has prevented us from extrapolating them to community-level predictions. Here, we leverage the availability of a long-term dataset from Zackenberg, Greenland (593 700 specimens collected between 1996 and 2014), to investigate how climate parameters influence the abundance of different arthropod groups and overall community composition. We find that variation in mean seasonal temperatures, winter duration and winter freeze–thaw events is correlated with taxon-specific and habitat-dependent changes in arthropod abundances. In addition, we find that arthropod communities have exhibited compositional changes consistent with the expected effects of recent shifts towards warmer active seasons and fewer freeze–thaw events in NE Greenland. Changes in community composition are up to five times more extreme in drier than wet habitats, with herbivores and parasitoids generally increasing in abundance, while the opposite is true for surface detritivores. These results suggest that species interactions and food web dynamics are changing in the Arctic, with potential implications for key ecosystem processes such as decomposition, nutrient cycling and primary productivity. PMID:29765633

Poleward upgliding Siberian atmospheric rivers over sea ice heat up Arctic upper air.

PubMed

Komatsu, Kensuke K; Alexeev, Vladimir A; Repina, Irina A; Tachibana, Yoshihiro

2018-02-13

We carried out upper air measurements with radiosondes during the summer over the Arctic Ocean from an icebreaker moving poleward from an ice-free region, through the ice edge, and into a region of thick ice. Rapid warming of the Arctic is a significant environmental issue that occurs not only at the surface but also throughout the troposphere. In addition to the widely accepted mechanisms responsible for the increase of tropospheric warming during the summer over the Arctic, we showed a new potential contributing process to the increase, based on our direct observations and supporting numerical simulations and statistical analyses using a long-term reanalysis dataset. We refer to this new process as "Siberian Atmospheric Rivers (SARs)". Poleward upglides of SARs over cold air domes overlying sea ice provide the upper atmosphere with extra heat via condensation of water vapour. This heating drives increased buoyancy and further strengthens the ascent and heating of the mid-troposphere. This process requires the combination of SARs and sea ice as a land-ocean-atmosphere system, the implication being that large-scale heat and moisture transport from the lower latitudes can remotely amplify the warming of the Arctic troposphere in the summer.

Differential arthropod responses to warming are altering the structure of Arctic communities.

PubMed

Koltz, Amanda M; Schmidt, Niels M; Høye, Toke T

2018-04-01

The Arctic is experiencing some of the fastest rates of warming on the planet. Although many studies have documented responses to such warming by individual species, the idiosyncratic nature of these findings has prevented us from extrapolating them to community-level predictions. Here, we leverage the availability of a long-term dataset from Zackenberg, Greenland (593 700 specimens collected between 1996 and 2014), to investigate how climate parameters influence the abundance of different arthropod groups and overall community composition. We find that variation in mean seasonal temperatures, winter duration and winter freeze-thaw events is correlated with taxon-specific and habitat-dependent changes in arthropod abundances. In addition, we find that arthropod communities have exhibited compositional changes consistent with the expected effects of recent shifts towards warmer active seasons and fewer freeze-thaw events in NE Greenland. Changes in community composition are up to five times more extreme in drier than wet habitats, with herbivores and parasitoids generally increasing in abundance, while the opposite is true for surface detritivores. These results suggest that species interactions and food web dynamics are changing in the Arctic, with potential implications for key ecosystem processes such as decomposition, nutrient cycling and primary productivity.

Data-driven modeling of surface temperature anomaly and solar activity trends

USGS Publications Warehouse

Friedel, Michael J.

2012-01-01

A novel two-step modeling scheme is used to reconstruct and analyze surface temperature and solar activity data at global, hemispheric, and regional scales. First, the self-organizing map (SOM) technique is used to extend annual modern climate data from the century to millennial scale. The SOM component planes are used to identify and quantify strength of nonlinear relations among modern surface temperature anomalies (<150 years), tropical and extratropical teleconnections, and Palmer Drought Severity Indices (0–2000 years). Cross-validation of global sea and land surface temperature anomalies verifies that the SOM is an unbiased estimator with less uncertainty than the magnitude of anomalies. Second, the quantile modeling of SOM reconstructions reveal trends and periods in surface temperature anomaly and solar activity whose timing agrees with published studies. Temporal features in surface temperature anomalies, such as the Medieval Warm Period, Little Ice Age, and Modern Warming Period, appear at all spatial scales but whose magnitudes increase when moving from ocean to land, from global to regional scales, and from southern to northern regions. Some caveats that apply when interpreting these data are the high-frequency filtering of climate signals based on quantile model selection and increased uncertainty when paleoclimatic data are limited. Even so, all models find the rate and magnitude of Modern Warming Period anomalies to be greater than those during the Medieval Warm Period. Lastly, quantile trends among reconstructed equatorial Pacific temperature profiles support the recent assertion of two primary El Niño Southern Oscillation types. These results demonstrate the efficacy of this alternative modeling approach for reconstructing and interpreting scale-dependent climate variables.

Nonlinear climate sensitivity and its implications for future greenhouse warming.

PubMed

Friedrich, Tobias; Timmermann, Axel; Tigchelaar, Michelle; Elison Timm, Oliver; Ganopolski, Andrey

2016-11-01

Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing-referred to as specific equilibrium climate sensitivity ( S )-is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth's future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections.

Nonlinear climate sensitivity and its implications for future greenhouse warming

PubMed Central

Friedrich, Tobias; Timmermann, Axel; Tigchelaar, Michelle; Elison Timm, Oliver; Ganopolski, Andrey

2016-01-01

Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing—referred to as specific equilibrium climate sensitivity (S)—is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth’s future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections. PMID:28861462

Tightening of tropical ascent and high clouds key to precipitation change in a warmer climate

PubMed Central

Su, Hui; Jiang, Jonathan H.; Neelin, J. David; Shen, T. Janice; Zhai, Chengxing; Yue, Qing; Wang, Zhien; Huang, Lei; Choi, Yong-Sang; Stephens, Graeme L.; Yung, Yuk L.

2017-01-01

The change of global-mean precipitation under global warming and interannual variability is predominantly controlled by the change of atmospheric longwave radiative cooling. Here we show that tightening of the ascending branch of the Hadley Circulation coupled with a decrease in tropical high cloud fraction is key in modulating precipitation response to surface warming. The magnitude of high cloud shrinkage is a primary contributor to the intermodel spread in the changes of tropical-mean outgoing longwave radiation (OLR) and global-mean precipitation per unit surface warming (dP/dTs) for both interannual variability and global warming. Compared to observations, most Coupled Model Inter-comparison Project Phase 5 models underestimate the rates of interannual tropical-mean dOLR/dTs and global-mean dP/dTs, consistent with the muted tropical high cloud shrinkage. We find that the five models that agree with the observation-based interannual dP/dTs all predict dP/dTs under global warming higher than the ensemble mean dP/dTs from the ∼20 models analysed in this study. PMID:28589940

Impacts of land cover changes on climate trends in Jiangxi province China.

PubMed

Wang, Qi; Riemann, Dirk; Vogt, Steffen; Glaser, Rüdiger

2014-07-01

Land-use/land-cover (LULC) change is an important climatic force, and is also affected by climate change. In the present study, we aimed to assess the regional scale impact of LULC on climate change using Jiangxi Province, China, as a case study. To obtain reliable climate trends, we applied the standard normal homogeneity test (SNHT) to surface air temperature and precipitation data for the period 1951-1999. We also compared the temperature trends computed from Global Historical Climatology Network (GHCN) datasets and from our analysis. To examine the regional impacts of land surface types on surface air temperature and precipitation change integrating regional topography, we used the observation minus reanalysis (OMR) method. Precipitation series were found to be homogeneous. Comparison of GHCN and our analysis on adjusted temperatures indicated that the resulting climate trends varied slightly from dataset to dataset. OMR trends associated with surface vegetation types revealed a strong surface warming response to land barrenness and weak warming response to land greenness. A total of 81.1% of the surface warming over vegetation index areas (0-0.2) was attributed to surface vegetation type change and regional topography. The contribution of surface vegetation type change decreases as land cover greenness increases. The OMR precipitation trend has a weak dependence on surface vegetation type change. We suggest that LULC integrating regional topography should be considered as a force in regional climate modeling.

The impact of different cooling strategies on urban air temperatures: the cases of Campinas, Brazil and Mendoza, Argentina

NASA Astrophysics Data System (ADS)

Alchapar, Noelia Liliana; Pezzuto, Claudia Cotrim; Correa, Erica Norma; Chebel Labaki, Lucila

2017-10-01

This paper describes different ways of reducing urban air temperature and their results in two cities: Campinas, Brazil—a warm temperate climate with a dry winter and hot summer (Cwa), and Mendoza, Argentina—a desert climate with cold steppe (BWk). A high-resolution microclimate modeling system—ENVI-met 3.1—was used to evaluate the thermal performance of an urban canyon in each city. A total of 18 scenarios were simulated including changes in the surface albedo, vegetation percentage, and the H/W aspect ratio of the urban canyons. These results revealed the same trend in behavior for each of the combinations of strategies evaluated in both cities. Nevertheless, these strategies produce a greater temperature reduction in the warm temperate climate (Cwa). Increasing the vegetation percentage reduces air temperatures and mean radiant temperatures in all scenarios. In addition, there is a greater decrease of urban temperature with the vegetation increase when the H/W aspect ratio is lower. Also, applying low albedo on vertical surfaces and high albedo on horizontal surfaces is successful in reducing air temperatures without raising the mean radiant temperature. The best combination of strategies—60 % of vegetation, low albedos on walls and high albedos on pavements and roofs, and 1.5 H/W—could reduce air temperatures up to 6.4 °C in Campinas and 3.5 °C in Mendoza.

ASTER Thermal Anomalies in Western Colorado

DOE Data Explorer

Richard E. Zehner

2013-01-01

This layer contains the areas identified as areas of anomalous surface temperature from ASTER satellite imagery. The temperature is calculated using the Emissivity Normalization Algorithm that separate temperature from emissivity. Areas that had temperature greater than 2o, and areas with temperature equal to 1o to 2o, were considered ASTER modeled very warm and warm surface exposures (thermal anomalies), respectively Note: 'o' is used in place of lowercase sigma in this description.

Aircraft Icing Handbook. Volume 1

DTIC Science & Technology

1991-03-01

Maryland - . . . Kohiman Aviation, Lawrence , Kansas Ohio State University, Columbus, Ohio .I --- t-r 1-- - -t I.Q,,- t ../e . Pratt and Whitney...lower; about six percent at -22 ’F (-30 *C). 1.2.3 Variations with Season The summer or warm season months create large warm air masses which can...on Aircraft Surfaces," NASA TM 87184, May 1986. 2-54 Hausman , R.J. and Turnock, S.R., "Investigation of Surface Water Behavior During Glaze Ice

Amplified North Atlantic warming in the late Pliocene by changes in Arctic gateways

DOE PAGES

Otto-Bliesner, Bette L.; Jahn, Alexandra; Feng, Ran; ...

2016-12-26

Under previous reconstructions of late Pliocene boundary conditions, climate models have failed to reproduce the warm sea surface temperatures reconstructed in the North Atlantic. Using a reconstruction of mid-Piacenzian paleogeography that has the Bering Strait and Canadian Arctic Archipelago Straits closed, however, improves the simulation of the proxy-indicated warm sea surface temperatures in the North Atlantic in the Community Climate System Model. We find that the closure of these small Arctic gateways strengthens the Atlantic Meridional Overturning Circulation, by inhibiting freshwater transport from the Pacific to the Arctic Ocean and from the Arctic Ocean to the Labrador Sea, leading tomore » warmer sea surface temperatures in the North Atlantic. In conclusion, this indicates that the state of the Arctic gateways may influence the sensitivity of the North Atlantic climate in complex ways, and better understanding of the state of these Arctic gateways for past time periods is needed.« less

The Hydrological Sensitivity to Global Warming and Solar Geoengineering Derived from Thermodynamic Constraints

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleidon, Alex; Kravitz, Benjamin S.; Renner, Maik

2015-01-16

We derive analytic expressions of the transient response of the hydrological cycle to surface warming from an extremely simple energy balance model in which turbulent heat fluxes are constrained by the thermodynamic limit of maximum power. For a given magnitude of steady-state temperature change, this approach predicts the transient response as well as the steady-state change in surface energy partitioning and the hydrologic cycle. We show that the transient behavior of the simple model as well as the steady state hydrological sensitivities to greenhouse warming and solar geoengineering are comparable to results from simulations using highly complex models. Many ofmore » the global-scale hydrological cycle changes can be understood from a surface energy balance perspective, and our thermodynamically-constrained approach provides a physically robust way of estimating global hydrological changes in response to altered radiative forcing.« less

The rogue nature of hiatuses in a global warming climate

NASA Astrophysics Data System (ADS)

Sévellec, F.; Sinha, B.; Skliris, N.

2016-08-01

The nature of rogue events is their unlikelihood and the recent unpredicted decade-long slowdown in surface warming, the so-called hiatus, may be such an event. However, given decadal variability in climate, global surface temperatures were never expected to increase monotonically with increasing radiative forcing. Here surface air temperature from 20 climate models is analyzed to estimate the historical and future likelihood of hiatuses and "surges" (faster than expected warming), showing that the global hiatus of the early 21st century was extremely unlikely. A novel analysis of future climate scenarios suggests that hiatuses will almost vanish and surges will strongly intensify by 2100 under a "business as usual" scenario. For "CO2 stabilisation" scenarios, hiatus, and surge characteristics revert to typical 1940s values. These results suggest to study the hiatus of the early 21st century and future reoccurrences as rogue events, at the limit of the variability of current climate modelling capability.

Coral-Derived Western Pacific Tropical Sea Surface Temperatures During the Last Millennium

NASA Astrophysics Data System (ADS)

Chen, Tianran; Cobb, Kim M.; Roff, George; Zhao, Jianxin; Yang, Hongqiang; Hu, Minhang; Zhao, Kuan

2018-04-01

Reconstructions of ocean temperatures prior to the industrial era serve to constrain natural climate variability on decadal to centennial timescales, yet relatively few such observations are available from the west Pacific Warm Pool. Here we present multiple coral-based sea surface temperature reconstructions from Yongle Atoll, in the South China Sea over the last 1,250 years (762-2013 Common Era [CE]). Reconstructed coral Sr/Ca-sea surface temperatures indicate that the "Little Ice Age (1711-1817 CE)" period was 0.7°C cooler than the "Medieval Climate Anomaly (913-1132 CE)" and that late 20th century warming of the western Pacific is likely unprecedented over the past millennium. Our findings suggest that the Western Pacific Warm Pool may have expanded (contracted) during the Medieval Climate Anomaly (Little Ice Age), leading to a strengthening (weakening) of the Asian summer monsoon, as recorded in Chinese stalagmites.

Cloud Feedback Key to Marine Heatwave off Baja California

NASA Astrophysics Data System (ADS)

Myers, Timothy A.; Mechoso, Carlos R.; Cesana, Gregory V.; DeFlorio, Michael J.; Waliser, Duane E.

2018-05-01

Between 2013 and 2015, the northeast Pacific Ocean experienced the warmest surface temperature anomalies in the modern observational record. This "marine heatwave" marked a shift of Pacific decadal variability to its warm phase and was linked to significant impacts on marine species as well as exceptionally arid conditions in western North America. Here we show that the subtropical signature of this warming, off Baja California, was associated with a record deficit in the spatial coverage of co-located marine boundary layer clouds. This deficit coincided with a large increase in downwelling solar radiation that dominated the anomalous energy budget of the upper ocean, resulting in record-breaking warm sea surface temperature anomalies. Our observation-based analysis suggests that a positive cloud-surface temperature feedback was key to the extreme intensity of the heatwave. The results demonstrate the extent to which boundary layer clouds can contribute to regional variations in climate.

Artificial Warming of Arctic Meadow under Pollution Stress: Experimental design

NASA Astrophysics Data System (ADS)

Moni, Christophe; Silvennoinen, Hanna; Fjelldal, Erling; Brenden, Marius; Kimball, Bruce; Rasse, Daniel

2014-05-01

Boreal and arctic terrestrial ecosystems are central to the climate change debate, notably because future warming is expected to be disproportionate as compared to world averages. Likewise, greenhouse gas (GHG) release from terrestrial ecosystems exposed to climate warming is expected to be the largest in the arctic. Artic agriculture, in the form of cultivated grasslands, is a unique and economically relevant feature of Northern Norway (e.g. Finnmark Province). In Eastern Finnmark, these agro-ecosystems are under the additional stressor of heavy metal and sulfur pollution generated by metal smelters of NW Russia. Warming and its interaction with heavy metal dynamics will influence meadow productivity, species composition and GHG emissions, as mediated by responses of soil microbial communities. Adaptation and mitigation measurements will be needed. Biochar application, which immobilizes heavy metal, is a promising adaptation method to promote positive growth response in arctic meadows exposed to a warming climate. In the MeadoWarm project we conduct an ecosystem warming experiment combined to biochar adaptation treatments in the heavy-metal polluted meadows of Eastern Finnmark. In summary, the general objective of this study is twofold: 1) to determine the response of arctic agricultural ecosystems under environmental stress to increased temperatures, both in terms of plant growth, soil organisms and GHG emissions, and 2) to determine if biochar application can serve as a positive adaptation (plant growth) and mitigation (GHG emission) strategy for these ecosystems under warming conditions. Here, we present the experimental site and the designed open-field warming facility. The selected site is an arctic meadow located at the Svanhovd Research station less than 10km west from the Russian mining city of Nikel. A splitplot design with 5 replicates for each treatment is used to test the effect of biochar amendment and a 3oC warming on the Arctic meadow. Ten circular split plots (diameter: 3.65 m & surface area: 10.5 m2) composed of one half amended with biochar and one control half not amended were prepared. Five of these plots are equipped with a warming system, while the other five were equipped with dummies. Each warmed plot is collocated with a control plot within one block. While split plots are all oriented in the same direction the position of blocks is randomized to eliminate the effect of the spatial variability. Biochar was incorporated in the first 20 cm of the soil with a rototiller. Warming system is provided by hexagonal arrays of infrared heaters. The temperature of the plots is monitored with infrared cameras. The 3oC increase of temperature is obtained by dynamically monitoring the temperature difference between warmed and control plots within blocks via improved software. Each plot is further equipped with a soil temperature and moisture sensor.

The phenology of Arctic Ocean surface warming.

PubMed

Steele, Michael; Dickinson, Suzanne

2016-09-01

In this work, we explore the seasonal relationships (i.e., the phenology) between sea ice retreat, sea surface temperature (SST), and atmospheric heat fluxes in the Pacific Sector of the Arctic Ocean, using satellite and reanalysis data. We find that where ice retreats early in most years, maximum summertime SSTs are usually warmer, relative to areas with later retreat. For any particular year, we find that anomalously early ice retreat generally leads to anomalously warm SSTs. However, this relationship is weak in the Chukchi Sea, where ocean advection plays a large role. It is also weak where retreat in a particular year happens earlier than usual, but still relatively late in the season, primarily because atmospheric heat fluxes are weak at that time. This result helps to explain the very different ocean warming responses found in two recent years with extreme ice retreat, 2007 and 2012. We also find that the timing of ice retreat impacts the date of maximum SST, owing to a change in the ocean surface buoyancy and momentum forcing that occurs in early August that we term the Late Summer Transition (LST). After the LST, enhanced mixing of the upper ocean leads to cooling of the ocean surface even while atmospheric heat fluxes are still weakly downward. Our results indicate that in the near-term, earlier ice retreat is likely to cause enhanced ocean surface warming in much of the Arctic Ocean, although not where ice retreat still occurs late in the season.

Changing surface-atmosphere energy exchange and refreezing capacity of the lower accumulation area, West Greenland

NASA Astrophysics Data System (ADS)

Charalampidis, C.; van As, D.; Box, J. E.; van den Broeke, M. R.; Colgan, W. T.; Doyle, S. H.; Hubbard, A. L.; MacFerrin, M.; Machguth, H.; Smeets, C. J. P. P.

2015-11-01

We present 5 years (2009-2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l. - above sea level) of the Greenland ice sheet in the Kangerlussuaq region. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater run-off. The observed run-off was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals an anomalously low 2012 summer-averaged albedo of 0.71 (typically ~ 0.78), as meltwater was present at the ice sheet surface. Consequently, during the 2012 melt season, the ice sheet surface absorbed 28 % (213 MJ m-2) more solar radiation than the average of all other years. A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity analysis reveals that 71 % of the additional solar radiation in 2012 was used for melt, corresponding to 36 % (0.64 m) of the 2012 surface lowering. The remaining 64 % (1.14 m) of surface lowering resulted from high atmospheric temperatures, up to a +2.6 °C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt-albedo feedback. Longer time series of SMB, regional temperature, and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year, with the lowest albedo, at this elevation on record. The warm conditions of recent years have resulted in enhanced melt and reduction of the refreezing capacity in the lower accumulation area. If high temperatures continue, the current lower accumulation area will turn into a region with superimposed ice in coming years.

Laboratory evaluation of a warm asphalt technology for use in Virginia.

DOT National Transportation Integrated Search

2008-01-01

Rising energy costs and increased environmental awareness have brought attention to the potential benefits of warm asphalt in the United States. Warm-mix asphalt (WMA) is produced by incorporating additives into asphalt mixtures to allow production a...

Early onset of industrial-era warming across the oceans and continents.

PubMed

Abram, Nerilie J; McGregor, Helen V; Tierney, Jessica E; Evans, Michael N; McKay, Nicholas P; Kaufman, Darrell S

2016-08-25

The evolution of industrial-era warming across the continents and oceans provides a context for future climate change and is important for determining climate sensitivity and the processes that control regional warming. Here we use post-ad 1500 palaeoclimate records to show that sustained industrial-era warming of the tropical oceans first developed during the mid-nineteenth century and was nearly synchronous with Northern Hemisphere continental warming. The early onset of sustained, significant warming in palaeoclimate records and model simulations suggests that greenhouse forcing of industrial-era warming commenced as early as the mid-nineteenth century and included an enhanced equatorial ocean response mechanism. The development of Southern Hemisphere warming is delayed in reconstructions, but this apparent delay is not reproduced in climate simulations. Our findings imply that instrumental records are too short to comprehensively assess anthropogenic climate change and that, in some regions, about 180 years of industrial-era warming has already caused surface temperatures to emerge above pre-industrial values, even when taking natural variability into account.

Future changes over the Himalayas: Mean temperature

NASA Astrophysics Data System (ADS)

Dimri, A. P.; Kumar, D.; Choudhary, A.; Maharana, P.

2018-03-01

An assessment of the projection of near surface air temperature over the Himalayan region from the COordinated Regional Climate Downscaling EXperiment- South Asia (hereafter, CORDEX-SA) regional climate model (RCM) experiments have been carried out for different Representative Concentration Pathway (RCP) scenarios. The purpose of this study is to assess the probable future changes in the mean temperature climatology and its long term trend for different seasons under greenhouse gas forcing scenarios for different seasons till the end of 21st century. A number of statistical measures such as changes in mean climatology, long term trend and probability distribution function have been used in order to detect the signals of changes in climate. Moreover, the associated uncertainties among different model experiments and their ensemble in space, time and different seasons in particular have been quantified. Despite of strong cold bias in the model experiments over Himalayan region (Nengker et al., 2017), statistically significant strong rate of warming (0.03-0.09 °C/year) across all the seasons and RCPs have been projected by all the models and their ensemble. Season specific response towards the warming is indicated by ensemble under future climate while ON season shows comparable magnitude of warming than DJF. Such warming intensifies with the increase in the radiative forcing under a range of greenhouse gas scenarios from RCP2.6 to RCP8.5. In addition to this, a wide range of spatial variability and disagreements in the trend magnitude between different models describes the uncertainty associated with the model projections and scenarios. A substantial seasonal response to warming with respect to elevation was also found, as DJF season followed by ON portrays highest rate of warming, specifically at higher elevation sites such as western Himalayas and northern part of central Himalayas. The different elevation classes respond differently to the projected future warming under different RCPs and seasons. Such higher warming during DJF may have consequences as changes in the fractional distribution of the solid and liquid precipitation as well as the melting of the glacial deposits with ultimately affecting the streamflow response and water resources in the downstream areas.

Process contributions to the intermodel spread in amplified Arctic warming

NASA Astrophysics Data System (ADS)

Boeke, R.; Taylor, P. C.

2016-12-01

The Arctic is warming at a rate more than twice the global average. This robust climate system response to an external forcing is referred to as Arctic Amplification (AA). While Coupled Model Intercomparison Project 5 (CMIP5) climate models simulate AA, the largest intermodel spread in projected warming is also found in the Arctic. Quantifying the amount of polar warming relative to global warming influences how society adapts to climate change; a 2°C increase in global mean temperature would result in a polar warming between 4-8°C according to the intermodel spread in CMIP5 simulations. A trove of previous work has considered AA diagnostically using variations in the surface energy budget to attribute the intermodel spread in AA to an assortment of feedbacks—surface albedo, cloud, surface turbulent flux, and atmospheric and oceanic energy transport. We consider a systems-thinking approach treating AA as a process that evolves over time. We hypothesize that two specific components of the AA process are most important and influence the intermodel spread. (1) The inability of the Arctic system to effectively remove excess heat sourced from natural variability. The change in the efficiency of the `Arctic air conditioner' is thought to be due to thinner and less extensive sea ice and the resulting ice albedo feedback. (2) The process through which energy is stored in the ocean and exchanged with the atmosphere within the context of the sea ice annual cycle is also important. This study uses CMIP5 simulations from the historical and RCP8.5 (Representative Concentration Pathway; an emission scenario with forcing increasing to 8.5 W m-2 by 2100) to analyze how the AA process operates in present and future climate. The intermodel spread in these processes and the influence on the spread in AA are discussed. This approach identifies models that more realistically simulate the AA process and will aid in narrowing intermodel spread in Arctic surface temperature projections.

Extreme Marine Warming Across Tropical Australia During Austral Summer 2015-2016

NASA Astrophysics Data System (ADS)

Benthuysen, Jessica A.; Oliver, Eric C. J.; Feng, Ming; Marshall, Andrew G.

2018-02-01

During austral summer 2015-2016, prolonged extreme ocean warming events, known as marine heatwaves (MHWs), occurred in the waters around tropical Australia. MHWs arose first in the southeast tropical Indian Ocean in November 2015, emerging progressively east until March 2016, when all waters from the North West Shelf to the Coral Sea were affected. The MHW maximum intensity tended to occur in March, coinciding with the timing of the maximum sea surface temperature (SST). Large areas were in a MHW state for 3-4 months continuously with maximum intensities over 2°C. In 2016, the Indonesian-Australian Basin and areas including the Timor Sea and Kimberley shelf experienced the longest and most intense MHW from remotely sensed SST dating back to 1982. In situ temperature data from temperature loggers at coastal sites revealed a consistent picture, with MHWs appearing from west to east and peaking in March 2016. Temperature data from moorings, an Argo float, and Slocum gliders showed the extent of warming with depth. The events occurred during a strong El Niño and weakened monsoon activity, enhanced by the extended suppressed phase of the Madden-Julian Oscillation. Reduced cloud cover in January and February 2016 led to positive air-sea heat flux anomalies into the ocean, predominantly due to the shortwave radiation contribution with a smaller additional contribution from the latent heat flux anomalies. A data-assimilating ocean model showed regional changes in the upper ocean circulation and a change in summer surface mixed layer depths and barrier layer thicknesses consistent with past El Niño events.

NASA Airborne Campaigns Focus on Climate Impacts in the Arctic

NASA Image and Video Library

2017-12-08

This red plane is a DHC-3 Otter, the plane flown in NASA's Operation IceBridge-Alaska surveys of mountain glaciers in Alaska. Credit: Chris Larsen, University of Alaska-Fairbanks Over the past few decades, average global temperatures have been on the rise, and this warming is happening two to three times faster in the Arctic. As the region’s summer comes to a close, NASA is hard at work studying how rising temperatures are affecting the Arctic. NASA researchers this summer and fall are carrying out three Alaska-based airborne research campaigns aimed at measuring greenhouse gas concentrations near Earth’s surface, monitoring Alaskan glaciers, and collecting data on Arctic sea ice and clouds. Observations from these NASA campaigns will give researchers a better understanding of how the Arctic is responding to rising temperatures. The Arctic Radiation – IceBridge Sea and Ice Experiment, or ARISE, is a new NASA airborne campaign to collect data on thinning sea ice and measure cloud and atmospheric properties in the Arctic. The campaign was designed to address questions about the relationship between retreating sea ice and the Arctic climate. Arctic sea ice reflects sunlight away from Earth, moderating warming in the region. Loss of sea ice means more heat from the sun is absorbed by the ocean surface, adding to Arctic warming. In addition, the larger amount of open water leads to more moisture in the air, which affects the formation of clouds that have their own effect on warming, either enhancing or reducing it. Read more: www.nasa.gov/earthrightnow NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Evaporation/SST Sensitivity Over the Tropical Oceans During ENSO Events as Estimated from the da Silva, Young, Levitus Surface Marine Data Set

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Fitzjarrald, D. E.; Sohn, B.-J.; Arnold, James E. (Technical Monitor)

2001-01-01

The da Silva, Young and Levitus Surface Marine Atlas, based on observations from the Comprehensive Ocean Atmosphere Data Set (COADS) Release 1, has been used to investigate the relationship between evaporation and sea-surface temperature (SST) over the global oceans. For the period 1950 to 1987 SST, surface latent heat flux, and other related variables have been filtered to minimize data uncertainties and to focus upon interannual variations associated with warm (El Nino) and cold (La Nina) ENSO events. Compositing procedures have enabled identification of systematic variations in latent heat fluxes accompanying these events and the relationship to spatial anomalies in ocean surface wind speed and humidity. The evaporation response associated with ENSO sea surface temperature (SST) variability is systematic in nature and composed of offsetting contributions from the surface wind and humidity variations. During warm events exceeding 1.0 S.D. delta SST, increases in the surface humidity deficit, delta(qs-qa), between the surface and 2m height dominate regions of positive SST anomalies and lead to increases in evaporation of almost 2 Wm (exp -2) at deltaSST = 0.23 K. Despite the increases in specific humidity, relative humidity decreases slightly in regions of elevated SSTs. For the most part, variations in wind speed are consistent with previous investigations. Weakening of the equatorial easterlies (and generation of westerlies) between 160 degrees E and 140 degrees W dominates during the early phases of warm events. Elevated wind speeds in adjacent subtropical regions and in the eastern equatorial Pacific subsequently develop too. The net contribution of these winds, which reflect adjustments in Hadley and Walker circulation components is toward reduced evaporation. Results for cold periods are approximately similar, but opposite in sign to warm events, though evidence of different temporal evolution is noted.

Acute Warm-up Effects in Submaximal Athletes: An EMG Study of Skilled Violinists.

PubMed

McCrary, J Matt; Halaki, Mark; Sorkin, Evgeny; Ackermann, Bronwen J

2016-02-01

Warm-up is commonly recommended for injury prevention and performance enhancement across all activities, yet this recommendation is not supported by evidence for repetitive submaximal activities such as instrumental music performance. The objective of this study is to quantify the effects of cardiovascular, core muscle, and musical warm-ups on muscle activity levels, musical performance, and subjective experience in skilled violinists. Fifty-five undergraduate, postgraduate, or professional violinists performed five randomly ordered 45-s musical excerpts of varying physical demands both before and after a randomly assigned 15-min, moderate-intensity cardiovascular, core muscle, musical (technical violin exercises), or inactive control warm-up protocol. Surface EMG data were obtained for 16 muscles of the trunk, shoulders, and right arm during each musical performance. Sound recording and perceived exertion (RPE) data were also obtained. Sound recordings were randomly ordered and rated for performance quality by blinded adjudicators. Questionnaire data regarding participant pain sites and fitness levels were used to stratify participants according to pain and fitness levels. Data were analyzed using two- and three-factor ANCOVA (surface EMG and sound recording) and Wilcoxon matched pairs tests (RPE). None of the three warm-up protocols had significant effects on muscle activity levels (P ≥ 0.10). Performance quality did not significantly increase (P ≥ 0.21). RPE significantly decreased (P < 0.05) after warm-up for each of the three experimental warm-ups; control condition RPE did not significantly decrease (P > 0.23). Acute physiological and musical benefits from cardiovascular, core muscle, and musical warm-ups in skilled violinists are limited to decreases in RPE. This investigation provides data from the performing arts in support of sports medical evidence suggesting that warm-up only effectively enhances maximal strength and power performance.

The coastal ocean response to the global warming acceleration and hiatus

PubMed Central

Liao, Enhui; Lu, Wenfang; Yan, Xiao-Hai; Jiang, Yuwu; Kidwell, Autumn

2015-01-01

Coastlines are fundamental to humans for habitation, commerce, and natural resources. Many coastal ecosystem disasters, caused by extreme sea surface temperature (SST), were reported when the global climate shifted from global warming to global surface warming hiatus after 1998. The task of understanding the coastal SST variations within the global context is an urgent matter. Our study on the global coastal SST from 1982 to 2013 revealed a significant cooling trend in the low and mid latitudes (31.4% of the global coastlines) after 1998, while 17.9% of the global coastlines changed from a cooling trend to a warming trend concurrently. The trend reversals in the Northern Pacific and Atlantic coincided with the phase shift of Pacific Decadal Oscillation and North Atlantic Oscillation, respectively. These coastal SST changes are larger than the changes of the global mean and open ocean, resulting in a fast increase of extremely hot/cold days, and thus extremely hot/cold events. Meanwhile, a continuous increase of SST was detected for a considerable portion of coastlines (46.7%) with a strengthened warming along the coastlines in the high northern latitudes. This suggests the warming still continued and strengthened in some regions after 1998, but with a weaker pattern in the low and mid latitudes. PMID:26568024

A century of ocean warming on Florida Keys coral reefs: historic in situ observations

USGS Publications Warehouse

Kuffner, Ilsa B.; Lidz, Barbara H.; Hudson, J. Harold; Anderson, Jeffery S.

2015-01-01

There is strong evidence that global climate change over the last several decades has caused shifts in species distributions, species extinctions, and alterations in the functioning of ecosystems. However, because of high variability on short (i.e., diurnal, seasonal, and annual) timescales as well as the recency of a comprehensive instrumental record, it is difficult to detect or provide evidence for long-term, site-specific trends in ocean temperature. Here we analyze five in situ datasets from Florida Keys coral reef habitats, including historic measurements taken by lighthouse keepers, to provide three independent lines of evidence supporting approximately 0.8 °C of warming in sea surface temperature (SST) over the last century. Results indicate that the warming observed in the records between 1878 and 2012 can be fully accounted for by the warming observed in recent decades (from 1975 to 2007), documented using in situ thermographs on a mid-shore patch reef. The magnitude of warming revealed here is similar to that found in other SST datasets from the region and to that observed in global mean surface temperature. The geologic context and significance of recent ocean warming to coral growth and population dynamics are discussed, as is the future prognosis for the Florida reef tract.

The dynamic monitoring of warm-water discharge based on the airborne high-resolution thermal infrared remote sensing data

NASA Astrophysics Data System (ADS)

Shao, Honglan; Xie, Feng; Liu, Chengyu; Liu, Zhihui; Zhang, Changxing; Yang, Gui; Wang, Jianyu

2016-04-01

The cooling water discharged from the coastal plants flow into the sea continuously, whose temperature is higher than original sea surface temperature (SST). The fact will have non-negligible influence on the marine environment in and around where the plants site. Hence, it's significant to monitor the temporal and spatial variation of the warm-water discharge for the assessment of the effect of the plant on its surrounding marine environment. The paper describes an approach for the dynamic monitoring of the warm-water discharge of coastal plants based on the airborne high-resolution thermal infrared remote sensing technology. Firstly, the geometric correction was carried out for the thermal infrared remote sensing images acquired on the aircraft. Secondly, the atmospheric correction method was used to retrieve the sea surface temperature of the images. Thirdly, the temperature-rising districts caused by the warm-water discharge were extracted. Lastly, the temporal and spatial variations of the warm-water discharge were analyzed through the geographic information system (GIS) technology. The approach was applied to Qinshan nuclear power plant (NPP), in Zhejiang Province, China. In considering with the tide states, the diffusion, distribution and temperature-rising values of the warm-water discharged from the plant were calculated and analyzed, which are useful to the marine environment assessment.

The coastal ocean response to the global warming acceleration and hiatus.

PubMed

Liao, Enhui; Lu, Wenfang; Yan, Xiao-Hai; Jiang, Yuwu; Kidwell, Autumn

2015-11-16

Coastlines are fundamental to humans for habitation, commerce, and natural resources. Many coastal ecosystem disasters, caused by extreme sea surface temperature (SST), were reported when the global climate shifted from global warming to global surface warming hiatus after 1998. The task of understanding the coastal SST variations within the global context is an urgent matter. Our study on the global coastal SST from 1982 to 2013 revealed a significant cooling trend in the low and mid latitudes (31.4% of the global coastlines) after 1998, while 17.9% of the global coastlines changed from a cooling trend to a warming trend concurrently. The trend reversals in the Northern Pacific and Atlantic coincided with the phase shift of Pacific Decadal Oscillation and North Atlantic Oscillation, respectively. These coastal SST changes are larger than the changes of the global mean and open ocean, resulting in a fast increase of extremely hot/cold days, and thus extremely hot/cold events. Meanwhile, a continuous increase of SST was detected for a considerable portion of coastlines (46.7%) with a strengthened warming along the coastlines in the high northern latitudes. This suggests the warming still continued and strengthened in some regions after 1998, but with a weaker pattern in the low and mid latitudes.

Growing importance of atmospheric water demands on the hydrologcial condition of East Asia

NASA Astrophysics Data System (ADS)

Park, C. E.; Ho, C. H.; Jeong, S. J.; Park, H.

2015-12-01

As global temperature increases, enhanced exchange of fresh water between the surface and atmosphere expected to make dry regions drier and wet regions wetter. This concept is well fitted for the ocean, but oversimplified for the land. How the climate change causes the complex patterns of the continental dryness change is one of challenging questions. Here we investigate the observed dryness changes of the land surface by examining the quantitative influence of several climate parameters on the background aridity changes over East Asia, containing various climate regimes from cold-arid to warm-humid regions, using observations of 189 stations covering the period from 1961 to 2010. Overall mean aridity trend is changed from negative to positive around early 1990s. The turning of dryness trend is largely influenced by sharp increase in atmospheric water demands, regardless of the background climate. The warming induced increase in water demands is larger in warm-humid regions than in cold-arid region due to the Clausius-Clapeyron relation between air temperature and saturation vapor pressure. The results show the drying of anthropogenic warming already begins and influences on the patterns of dryness change over the land surface.

Evapotranspiration Cycles in a High Latitude Agroecosystem: Potential Warming Role

PubMed Central

Ruairuen, Watcharee

2015-01-01

As the acreages of agricultural lands increase, changes in surface energetics and evapotranspiration (ET) rates may arise consequently affecting regional climate regimes. The objective of this study was to evaluate summertime ET dynamics and surface energy processes in a subarctic agricultural farm in Interior Alaska. The study includes micrometeorological and hydrological data. Results covering the period from June to September 2012 and 2013 indicated consistent energy fractions: LE/R net (67%), G/R net (6%), H/R net (27%) where LE is latent heat flux, R net is the surface net radiation, G is ground heat flux and H is the sensible heat flux. Additionally actual surface evapotranspiration from potential evaporation was found to be in the range of 59 to 66%. After comparing these rates with those of most prominent high latitude ecosystems it is argued here that if agroecosystem in high latitudes become an emerging feature in the land-use, the regional surface energy balance will significantly shift in comparison to existing Arctic natural ecosystems. PMID:26368123

Evapotranspiration Cycles in a High Latitude Agroecosystem: Potential Warming Role.

PubMed

Ruairuen, Watcharee; Fochesatto, Gilberto J; Sparrow, Elena B; Schnabel, William; Zhang, Mingchu; Kim, Yongwon

2015-01-01

As the acreages of agricultural lands increase, changes in surface energetics and evapotranspiration (ET) rates may arise consequently affecting regional climate regimes. The objective of this study was to evaluate summertime ET dynamics and surface energy processes in a subarctic agricultural farm in Interior Alaska. The study includes micrometeorological and hydrological data. Results covering the period from June to September 2012 and 2013 indicated consistent energy fractions: LE/Rnet (67%), G/Rnet (6%), H/Rnet (27%) where LE is latent heat flux, Rnet is the surface net radiation, G is ground heat flux and H is the sensible heat flux. Additionally actual surface evapotranspiration from potential evaporation was found to be in the range of 59 to 66%. After comparing these rates with those of most prominent high latitude ecosystems it is argued here that if agroecosystem in high latitudes become an emerging feature in the land-use, the regional surface energy balance will significantly shift in comparison to existing Arctic natural ecosystems.

A preliminary study of the tropical water cycle and its sensitivity to surface warming

NASA Technical Reports Server (NTRS)

Lau, K. M.; Sui, C. H.; Tao, W. K.

1993-01-01

The Goddard Cumulus Ensemble Model (GCEM) has been used to demonstrate that cumulus-scale dynamics and microphysics play a major role in determining the vertical distribution of water vapor and clouds in the tropical atmosphere. The GCEM is described and is the basic structure of cumulus convection. The long-term equilibrium response to tropical convection to surface warming is examined. A picture of the water cycle within tropical cumulus clusters is developed.

Western Pacific Warm Pool expansion event during 2.0-1.5 Ma and its implications to global climate dynamics

NASA Astrophysics Data System (ADS)

Lo, L.; Chuang, C. K.; Wei, K. Y.; Shen, C. C.; Mii, H. S.; Chang, Y. P.

2017-12-01

In this study, we reconstruct surface and upper thermocline seawater temperatures by using planktonic foraminifera Globigerinoides sacculifer and Neogloboquadrina deutertrei in the southern Western Pacific Warm Pool (S-WPWP, ODP Site 1115B, 9o11'S, 151o34'E, water depth 1149 m) during past 2.2-1.1 million years (Ma). Significant S-WPWP surface warming in both glacial and interglacial periods during 1.86-1.55 Ma is accompanied with gradual upper thermocline cooling. S-WPWP sea surface temperature dropped 2.1oC from 1.50-1.21 Ma but upper thermocline temperature further decreased 1.1oC at this time period. WPWP expansion event is also supported by vertical foraminiferal Mg/Ca-derived temperature profile records in the central WPWP (ODP Site 806, Ford et al. 2015). Although foraminiferal Mg/Ca-derived temperature records from Eastern Equatorial Pacific suggests long-term cooling trend (Wara et al. 2005), alkenone undersaturation index (UK'37)-inferred surface temperature records suggest 1oC warming during 2.0-1.5 Ma (Fedorov et al. 2013). We argue that seasonal expansion of WPWP may be attributable to the meridional thermocline gradient increasing (Martinez-Garcia et al. 2010) during 2.0-1.5 Ma. Long-term extent variability of WPWP could have impact on cross-equatorial energy transportation and meridional precipitation belt movements (Lo et al., 2014).

Sustained Observations of Air-Sea Fluxes and Air-Sea Interaction at the Stratus Ocean Reference Station

NASA Astrophysics Data System (ADS)

Weller, Robert

2014-05-01

Since October 2000, a well-instrumented surface mooring has been maintained some 1,500 km west of the coast of northern Chile, roughly in the location of the climatological maximum in marine stratus clouds. Statistically significant increases in wind stress and decreases in annual net air-sea heat flux and in latent heat flux have been observed. If the increased oceanic heat loss continues, the region will within the next decade change from one of net annual heat gain by the ocean to one of neat annual heat loss. Already, annual evaporation of about 1.5 m of sea water a year acts to make the warm, salty surface layer more dense. Of interest is examining whether or not increased oceanic heat loss has the potential to change the structure of the upper ocean and potentially remove the shallow warm, salty mixed layer that now buffers the atmosphere from the interior ocean. Insights into how that warm, shallow layer is formed and maintained come from looking at oceanic response to the atmosphere at diurnal tie scales. Restratification each spring and summer is found to depend upon the occurrence of events in which the trade winds decay, allowing diurnal warming in the near-surface ocean to occur, and when the winds return resulting in a net upward step in sea surface temperature. This process is proving hard to accurately model.

Distribution of a pelagic tunicate, Salpa fusiformis in warm surface current of the eastern Korean waters and its impingement on cooling water intakes of Uljin nuclear power plant.

PubMed

Chae, Jinho; Choi, Hyun Woo; Lee, Woo Jin; Kim, Dongsung; Lee, Jae Hac

2008-07-01

Impingement of a large amount of gelatinous plankton, Salpa fusiformis on the seawater intake system-screens in a nuclear power plant at Uljin was firstly recorded on 18th June 2003. Whole amount of the clogged animals was estimated were presumptively at 295 tons and the shortage of cooling seawater supply by the animal clogging caused 38% of decrease in generation capability of the power plant. Zooplankton collection with a multiple towing net during the day and at night from 5 to 6 June 2003 included various gelatinous zooplanktons known to be warm water species such as salps and siphonophores. Comparatively larger species, Salpa fusiformis occupied 25.4% in individual density among the gelatinous plankton and showed surface distribution in the depth shallower than thermocline, performing little diel vertical migration. Temperature, salinity and satellite data also showed warm surface current predominated over the southern coastal region near the power plant in June. The results suggested that warm surface current occasionally extended into the neritic region may transfer S. fusiformis, to the waters off the power plant. The environmental factors and their relation to ecobiology of the large quantity of salpa population that are being sucked into the intake channel of the power plant are discussed.

Investigating warming trends and spatial patterns of Land Surface Temperatures over the Greater Los Angeles Area using new MODIS and VIIRS LST products

NASA Astrophysics Data System (ADS)

Malakar, N. K.; Hulley, G. C.

2016-12-01

The Los Angeles (LA) metropolitan area is one of the fastest growing urban centers in the United States, and home to roughly 18 million people. Understanding the trends and impacts of warming temperatures in urban environments is an increasingly important issue in our changing climate. We used thermal infrared data from Moderate Resolution Imaging Spectroradiometer (MODIS), and Visible Infrared Imaging Radiometer Suite (VIIRS) sensors to retrieve Land Surface Temperature using a new Temperature Emissivity Separation algorithm adapted for these sensors. We analyzed day and night LST retrievals to study the warming trends of LST for the greater LA region from 2002-2015. The average warming trend over LA for summer days and nights over this period for MODIS Aqua data was 1.1 °C per decade, while a more rapid warming is observed for the years 2012-2016 for both MODIS and VIIRS observations. We have also found that inland LA regions are warming more rapidly than the other regions. We further investigate the underlying cause of the warming by looking into the physical factors such as changes in net radiation, cloud cover, and evapotranspiration. The results will help to understand how indicators of climate change are evolving in the beginning of the 21st century, and how they compare with global climate model projections. Identification of potential impacts, and underlying causes of warming trends in various LA regions will help decision makers to develop policies to help mitigate the effects of rising temperatures.

The linkage between stratospheric water vapor and surface temperature in an observation-constrained coupled general circulation model

NASA Astrophysics Data System (ADS)

Wang, Yuan; Su, Hui; Jiang, Jonathan H.; Livesey, Nathaniel J.; Santee, Michelle L.; Froidevaux, Lucien; Read, William G.; Anderson, John

2017-04-01

We assess the interactions between stratospheric water vapor (SWV) and surface temperature during the past two decades using satellite observations and the Community Earth System Model (CESM). From 1992 to 2013, to first order, the observed SWV exhibited three distinct piece-wise trends: a steady increase from 1992 to 2000, an abrupt drop from 2000 to 2004, and a gradual recovery after 2004, while the global-mean surface temperature experienced a strong increase until 2000 and a warming hiatus after 2000. The atmosphere-only CESM shows that the seasonal variation of tropical-mean (30°S-30°N) SWV is anticorrelated with that of the tropical-mean sea surface temperature (SST), while the correlation between the tropical SWV and SST anomalies on the interannual time scale is rather weak. By nudging the modeled SWV to prescribed profiles in coupled atmosphere-slab ocean experiments, we investigate the impact of SWV variations on surface temperature change. We find that a uniform 1 ppmv (0.5 ppmv) SWV increase (decrease) leads to an equilibrium global mean surface warming (cooling) of 0.12 ± 0.05 °C (-0.07 ± 0.05 °C). Sensitivity experiments show that the equilibrium response of global mean surface temperature to SWV perturbations over the extratropics is larger than that over the tropics. The observed sudden drop of SWV from 2000 to 2004 produces a global mean surface cooling of about -0.048 ± 0.041 °C, which suggests that a persistent change in SWV would make an imprint on long-term variations of global-mean surface temperature. A constant linear increase in SWV based on the satellite-observed rate of SWV change yields a global mean surface warming of 0.03 ± 0.01 °C/decade over a 50-year period, which accounts for about 19 % of the observed surface temperature increase prior to the warming hiatus. In the same experiment, trend analyses during different periods reveal a multi-year adjustment of surface temperature before the response to SWV forcing becomes strong relative to the internal variability in the model.

The recent warming of permafrost in Alaska

NASA Astrophysics Data System (ADS)

Osterkamp, T. E.

2005-12-01

This paper reports results of an experiment initiated in 1977 to determine the effects of climate on permafrost in Alaska. Permafrost observatories with boreholes were established along a north-south transect of Alaska in undisturbed permafrost terrain. The analysis and interpretation of annual temperature measurements in the boreholes and daily temperature measurements of the air, ground and permafrost surfaces made with automated temperature loggers are reported. Permafrost temperatures warmed along this transect coincident with a statewide warming of air temperatures that began in 1977. At two sites on the Arctic Coastal Plain, the warming was seasonal, greatest during "winter" months (October through May) and least during "summer" months (June through September). Permafrost temperatures peaked in the early 1980s and then decreased in response to slightly cooler air temperatures and thinner snow covers. Arctic sites began warming again typically about 1986 and Interior Alaska sites about 1988. Gulkana, the southernmost site, has been warming slowly since it was drilled in 1983. Air temperatures were relatively warm and snow covers were thicker-than-normal from the late 1980s into the late 1990s allowing permafrost temperatures to continue to warm. Temperatures at some sites leveled off or cooled slightly at the turn of the century. Two sites (Yukon River Bridge and Livengood) cooled during the period of observations. The magnitude of the total warming at the surface of the permafrost (through 2003) was 3 to 4 °C for the Arctic Coastal Plain, 1 to 2 °C for the Brooks Range including its northern and southern foothills, and 0.3 to 1 °C south of the Yukon River. While the data are sparse, permafrost is warming throughout the region north of the Brooks Range, southward along the transect from the Brooks Range to the Chugach Mountains (except for Yukon River and Livengood), in Interior Alaska throughout the Tanana River region, and in the region south of the Alaska Range from Tok westward to Gulkana (in the Copper River Valley) and beyond to the Talkeetna Mountains. Thermal offset allows permafrost to survive in the presence of positive annual mean ground surface temperatures and was observed repeatedly since 1987 at two sites. The observed warming has not produced an increasing trend in maximum active layer thicknesses due to its seasonality. Near Healy, permafrost has been thawing at the top since the late 1980s at about 10 cm/yr. At Gulkana, permafrost was thawing from the bottom at a rate of 4 cm/yr that accelerated to 9 cm/yr after 2000.

Impacts of peatland forestation on regional climate conditions in Finland

NASA Astrophysics Data System (ADS)

Gao, Yao; Markkanen, Tiina; Backman, Leif; Henttonen, Helena M.; Pietikäinen, Joni-Pekka; Laaksonen, Ari

2014-05-01

Climate response to anthropogenic land cover change happens more locally and occurs on a shorter time scale than the global warming due to increased GHGs. Over the second half of last Century, peatlands were vastly drained in Finland to stimulate forest growth for timber production. In this study, we investigate the biophysical effects of peatland forestation on near-surface climate conditions in Finland. For this, the regional climate model REMO, developed in Max Plank Institute (currently in Climate Service Center, Germany), provides an effective way. Two sets of 15-year climate simulations were done by REMO, using the historic (1920s; The 1st Finnish National Forest Inventory) and present-day (2000s; the 10th Finnish National Forest Inventory) land cover maps, respectively. The simulated surface air temperature and precipitation were then analyzed. In the most intensive peatland forestation area in Finland, the differences in monthly averaged daily mean surface air temperature show a warming effect around 0.2 to 0.3 K in February and March and reach to 0.5 K in April, whereas a slight cooling effect, less than 0.2 K, is found from May till October. Consequently, the selected snow clearance dates in model gridboxes over that area are advanced 0.5 to 4 days in the mean of 15 years. The monthly averaged precipitation only shows small differences, less than 10 mm/month, in a varied pattern in Finland from April to September. Furthermore, a more detailed analysis was conducted on the peatland forestation area with a 23% decrease in peatland and a 15% increase in forest types. 11 day running means of simulated temperature and energy balance terms, as well as snow depth were averaged over 15 years. Results show a positive feedback induced by peatland forestation between the surface air temperature and snow depth in snow melting period. This is because the warmer temperature caused by lower surface albedo due to more forest in snow cover period leads to a quicker and earlier snow melting. Meanwhile, surface albedo is reduced and consequently surface air temperature is increased. Additionally, the maximum difference from individual gridboxes in this area over 15 years of 11 day running means of daily mean surface air temperature reaches 2 K, which is four times as much as the maximum difference of 15-year regional average of that. This illustrates that the spring warming effect from peatland forestation in Finland is highly heterogeneous spatially and temporally.

Reconciling controversies about the ‘global warming hiatus’

NASA Astrophysics Data System (ADS)

Medhaug, Iselin; Stolpe, Martin B.; Fischer, Erich M.; Knutti, Reto

2017-05-01

Between about 1998 and 2012, a time that coincided with political negotiations for preventing climate change, the surface of Earth seemed hardly to warm. This phenomenon, often termed the ‘global warming hiatus’, caused doubt in the public mind about how well anthropogenic climate change and natural variability are understood. Here we show that apparently contradictory conclusions stem from different definitions of ‘hiatus’ and from different datasets. A combination of changes in forcing, uptake of heat by the oceans, natural variability and incomplete observational coverage reconciles models and data. Combined with stronger recent warming trends in newer datasets, we are now more confident than ever that human influence is dominant in long-term warming.

Reconciling controversies about the 'global warming hiatus'.

PubMed

Medhaug, Iselin; Stolpe, Martin B; Fischer, Erich M; Knutti, Reto

2017-05-03

Between about 1998 and 2012, a time that coincided with political negotiations for preventing climate change, the surface of Earth seemed hardly to warm. This phenomenon, often termed the 'global warming hiatus', caused doubt in the public mind about how well anthropogenic climate change and natural variability are understood. Here we show that apparently contradictory conclusions stem from different definitions of 'hiatus' and from different datasets. A combination of changes in forcing, uptake of heat by the oceans, natural variability and incomplete observational coverage reconciles models and data. Combined with stronger recent warming trends in newer datasets, we are now more confident than ever that human influence is dominant in long-term warming.

Investigating the impact of land-use land-cover change on Indian summer monsoon daily rainfall and temperature during 1951–2005 using a regional climate model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halder, Subhadeep; Saha, Subodh K.; Dirmeyer, Paul A.

Daily moderate rainfall events, which constitute a major portion of seasonal summer monsoon rainfall over central India, have decreased significantly during the period 1951 through 2005. On the other hand, mean and extreme near-surface daily temperature during the monsoon season have increased by a maximum of 1–1.5 °C. Using simulations made with a high-resolution regional climate model (RegCM4) and prescribed land cover of years 1950 and 2005, it is demonstrated that part of the changes in moderate rainfall events and temperature have been caused by land-use/land-cover change (LULCC), which is mostly anthropogenic. Model simulations show that the increase in seasonal mean and extreme temperature over centralmore » India coincides with the region of decrease in forest and increase in crop cover. Our results also show that LULCC alone causes warming in the extremes of daily mean and maximum temperatures by a maximum of 1–1.2 °C, which is comparable with the observed increasing trend in the extremes. Decrease in forest cover and simultaneous increase in crops not only reduces the evapotranspiration over land and large-scale convective instability, but also contributes toward decrease in moisture convergence through reduced surface roughness. These factors act together in reducing significantly the moderate rainfall events and the amount of rainfall in that category over central India. Additionally, the model simulations are repeated by removing the warming trend in sea surface temperatures over the Indian Ocean. As a result, enhanced warming at the surface and greater decrease in moderate rainfall events over central India compared to the earlier set of simulations are noticed. Results from these additional experiments corroborate our initial findings and confirm the contribution of LULCC in the decrease in moderate rainfall events and increase in daily mean and extreme temperature over India. Therefore, this study demonstrates the important implications of LULCC over India during the monsoon season. Although, the regional climate model helps in better resolving land–atmosphere feedbacks over the Indian region, the inferences do depend on the fidelity of the model in capturing the features of Indian monsoon realistically. Lastly, it is proposed that similar studies using a suite of climate models will further enrich our understanding about the role of LULCC in the Indian monsoon climate.« less

Investigating the impact of land-use land-cover change on Indian summer monsoon daily rainfall and temperature during 1951–2005 using a regional climate model

DOE PAGES

Halder, Subhadeep; Saha, Subodh K.; Dirmeyer, Paul A.; ...

2016-05-10

Daily moderate rainfall events, which constitute a major portion of seasonal summer monsoon rainfall over central India, have decreased significantly during the period 1951 through 2005. On the other hand, mean and extreme near-surface daily temperature during the monsoon season have increased by a maximum of 1–1.5 °C. Using simulations made with a high-resolution regional climate model (RegCM4) and prescribed land cover of years 1950 and 2005, it is demonstrated that part of the changes in moderate rainfall events and temperature have been caused by land-use/land-cover change (LULCC), which is mostly anthropogenic. Model simulations show that the increase in seasonal mean and extreme temperature over centralmore » India coincides with the region of decrease in forest and increase in crop cover. Our results also show that LULCC alone causes warming in the extremes of daily mean and maximum temperatures by a maximum of 1–1.2 °C, which is comparable with the observed increasing trend in the extremes. Decrease in forest cover and simultaneous increase in crops not only reduces the evapotranspiration over land and large-scale convective instability, but also contributes toward decrease in moisture convergence through reduced surface roughness. These factors act together in reducing significantly the moderate rainfall events and the amount of rainfall in that category over central India. Additionally, the model simulations are repeated by removing the warming trend in sea surface temperatures over the Indian Ocean. As a result, enhanced warming at the surface and greater decrease in moderate rainfall events over central India compared to the earlier set of simulations are noticed. Results from these additional experiments corroborate our initial findings and confirm the contribution of LULCC in the decrease in moderate rainfall events and increase in daily mean and extreme temperature over India. Therefore, this study demonstrates the important implications of LULCC over India during the monsoon season. Although, the regional climate model helps in better resolving land–atmosphere feedbacks over the Indian region, the inferences do depend on the fidelity of the model in capturing the features of Indian monsoon realistically. Lastly, it is proposed that similar studies using a suite of climate models will further enrich our understanding about the role of LULCC in the Indian monsoon climate.« less

Eocene climate and Arctic paleobathymetry: A tectonic sensitivity study using GISS ModelE-R

NASA Astrophysics Data System (ADS)

Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

2009-12-01

The early Paleogene (65-45 million years ago, Ma) was a ‘greenhouse’ interval with global temperatures warmer than any other time in the last 65 Ma. This period was characterized by high levels of CO2, warm high-latitudes, warm surface-and-deep oceans, and an intensified hydrological cycle. Sediments from the Arctic suggest that the Eocene surface Arctic Ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions remain uncertain. We present equilibrium climate conditions derived from a fully-coupled, water-isotope enabled, general circulation model (GISS ModelE-R) configured for the early Eocene. We also present model-data comparison plots for key climatic variables (SST and δ18O) and analyses of the leading modes of variability in the tropical Pacific and North Atlantic regions. Our tectonic sensitivity study indicates that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the seaways connecting the Arctic to the Atlantic and Tethys. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~6 psu and warming of sea-surface temperatures by 2°C in the North Atlantic and 5-10°C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We also suggest that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates in the Atlantic.

Hydrographic and fish larvae distribution during the "Godzilla El Niño 2015-2016" in the northern end of the shallow oxygen minimum zone of the Eastern Tropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Sánchez-Velasco, L.; Beier, E.; Godínez, V. M.; Barton, E. D.; Santamaría-del-Angel, E.; Jiménez-Rosemberg, S. P. A.; Marinone, S. G.

2017-03-01

Based on hydrographic data and vertical distributions of tropical species of fish larvae (Diogenichthys laternatus, Vinciguerria lucetia, Bregmaceros bathymaster, and Auxis spp.), effects of "Godzilla El Niño 2015-2016" in the shallow oxygen minimum zone off Mexico were analyzed. Zooplankton samples were collected during four cruises, before (February 2010 and April 2012) and during (June 2015 and March 2016) the warm event. Temporal series of sea surface temperature revealed that June 2015 was the warmest June of the last years. Conservative temperature was >2°C higher than normal in the surface mixed layer, and the suboxic layer (4.4 µmol/kg) reached as shallow as 100 m depth. Unexpected results were that larval abundances were relatively high during the warm event, unlike zooplankton volumes, which declined. Before the warm event, V. lucetia and Auxis spp. were more abundant in the surface mixed layer, while B. bathymaster and D. laternatus dominated in the thermocline and shallow hypoxic layer (44 µmol/kg). However, during the event in June 2015, all species were most abundant in the surface mixed layer, which implied that the species adapted to hypoxia had inverted their normal pattern of distribution, possibly as consequence of the rise of the suboxic layer; however, further observations are required to confirm this generality. Results showed no dramatic change in the total larval abundance during the warm event. Nevertheless, a differential response in their vertical distribution was evident in association with changes in the depth of the shallow hypoxic and suboxic layers. This might indicate adaptability of tropical species to prolonged periods of warming in the oceans.

Enhanced deep ocean ventilation and oxygenation with global warming

NASA Astrophysics Data System (ADS)

Froelicher, T. L.; Jaccard, S.; Dunne, J. P.; Paynter, D.; Gruber, N.

2014-12-01

Twenty-first century coupled climate model simulations, observations from the recent past, and theoretical arguments suggest a consistent trend towards warmer ocean temperatures and fresher polar surface oceans in response to increased radiative forcing resulting in increased upper ocean stratification and reduced ventilation and oxygenation of the deep ocean. Paleo-proxy records of the warming at the end of the last ice age, however, suggests a different outcome, namely a better ventilated and oxygenated deep ocean with global warming. Here we use a four thousand year global warming simulation from a comprehensive Earth System Model (GFDL ESM2M) to show that this conundrum is a consequence of different rates of warming and that the deep ocean is actually better ventilated and oxygenated in a future warmer equilibrated climate consistent with paleo-proxy records. The enhanced deep ocean ventilation in the Southern Ocean occurs in spite of increased positive surface buoyancy fluxes and a constancy of the Southern Hemisphere westerly winds - circumstances that would otherwise be expected to lead to a reduction in deep ocean ventilation. This ventilation recovery occurs through a global scale interaction of the Atlantic Meridional Overturning Circulation undergoing a multi-centennial recovery after an initial century of transient decrease and transports salinity-rich waters inform the subtropical surface ocean to the Southern Ocean interior on multi-century timescales. The subsequent upwelling of salinity-rich waters in the Southern Ocean strips away the freshwater cap that maintains vertical stability and increases open ocean convection and the formation of Antarctic Bottom Waters. As a result, the global ocean oxygen content and the nutrient supply from the deep ocean to the surface are higher in a warmer ocean. The implications for past and future changes in ocean heat and carbon storage will be discussed.

Effects of two warm-mix additives on aging, rheological and failure properties of asphalt cements

NASA Astrophysics Data System (ADS)

Omari, Isaac Obeng

Sustainable road construction and maintenance could be supported when excellent warm-mix additives are employed in the modification of asphalt. These warm-mix additives provide remedies for today's requirements such as fatigue cracking resistance, durability, thermal cracking resistance, rutting resistance and resistance to moisture damage. Warm-mix additives are based on waxes and surfactants which reduce energy consumption and carbon dioxide emissions significantly during the construction phase of the pavement. In this study, the effects of two warm mix additives, siloxane and oxidised polyethylene wax, on roofing asphalt flux (RAF) and asphalt modified with waste engine oil (655-7) were investigated to evaluate the rheological, aging and failure properties of the asphalt binders. In terms of the properties of these two different asphalts, RAF has proved to be superior quality asphalt whereas 655-7 is poor quality asphalt. The properties of the modified asphalt samples were measured by Superpave(TM) tests such as Dynamic Shear Rheometer (DSR) test and Bending Beam Rheometer (BBR) test as well as modified protocols such as the extended BBR (eBBR) test (LS-308) and the Double- Edge-Notched Tension (DENT) test (LS-299) after laboratory aging. In addition, the Avrami theory was used to gain an insight on the crystallization of asphalt or the waxes within the asphalt binder. This study has however shown that the eBBR and DENT tests are better tools for providing accurate specification tests to curb thermal and fatigue cracking in contemporary asphalt pavements.

Soil crusts to warm the planet

NASA Astrophysics Data System (ADS)

Garcia-Pichel, Ferran; Couradeau, Estelle; Karaoz, Ulas; da Rocha Ulisses, Nunes; Lim Hsiao, Chiem; Northen, Trent; Brodie, Eoin

2016-04-01

Soil surface temperature, an important driver of terrestrial biogeochemical processes, depends strongly on soil albedo, which can be significantly modified by factors such as plant cover. In sparsely vegetated lands, the soil surface can also be colonized by photosynthetic microbes that build biocrust communities. We used concurrent physical, biochemical and microbiological analyses to show that mature biocrusts can increase surface soil temperature by as much as 10 °C through the accumulation of large quantities of a secondary metabolite, the microbial sunscreen scytonemin, produced by a group of late-successional cyanobacteria. Scytonemin accumulation decreases soil albedo significantly. Such localized warming had apparent and immediate consequences for the crust soil microbiome, inducing the replacement of thermosensitive bacterial species with more thermotolerant forms. These results reveal that not only vegetation but also microorganisms are a factor in modifying terrestrial albedo, potentially impacting biosphere feedbacks on past and future climate, and call for a direct assessment of such effects at larger scales. Based on estimates of the global biomass of cyanobacteria in soil biocrusts, one can easily calculate that there must currently exist about 15 million metric tons of scytonemin at work, warming soil surfaces worldwide

Global Surface Temperature Change and Uncertainties Since 1861

NASA Technical Reports Server (NTRS)

Shen, Samuel S. P.; Lau, William K. M. (Technical Monitor)

2002-01-01

The objective of this talk is to analyze the warming trend and its uncertainties of the global and hemi-spheric surface temperatures. By the method of statistical optimal averaging scheme, the land surface air temperature and sea surface temperature observational data are used to compute the spatial average annual mean surface air temperature. The optimal averaging method is derived from the minimization of the mean square error between the true and estimated averages and uses the empirical orthogonal functions. The method can accurately estimate the errors of the spatial average due to observational gaps and random measurement errors. In addition, quantified are three independent uncertainty factors: urbanization, change of the in situ observational practices and sea surface temperature data corrections. Based on these uncertainties, the best linear fit to annual global surface temperature gives an increase of 0.61 +/- 0.16 C between 1861 and 2000. This lecture will also touch the topics on the impact of global change on nature and environment. as well as the latest assessment methods for the attributions of global change.

Simulated versus observed patterns of warming over the extratropical Northern Hemisphere continents during the cold season

PubMed Central

Wallace, John M.; Fu, Qiang; Smoliak, Brian V.; Lin, Pu; Johanson, Celeste M.

2012-01-01

A suite of the historical simulations run with the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) models forced by greenhouse gases, aerosols, stratospheric ozone depletion, and volcanic eruptions and a second suite of simulations forced by increasing CO2 concentrations alone are compared with observations for the reference interval 1965–2000. Surface air temperature trends are disaggregated by boreal cold (November-April) versus warm (May-October) seasons and by high latitude northern (N: 40°–90 °N) versus southern (S: 60 °S–40 °N) domains. A dynamical adjustment is applied to remove the component of the cold-season surface air temperature trends (over land areas poleward of 40 °N) that are attributable to changing atmospheric circulation patterns. The model simulations do not simulate the full extent of the wintertime warming over the high-latitude Northern Hemisphere continents during the later 20th century, much of which was dynamically induced. Expressed as fractions of the concurrent trend in global-mean sea surface temperature, the relative magnitude of the dynamically induced wintertime warming over domain N in the observations, the simulations with multiple forcings, and the runs forced by the buildup of greenhouse gases only is 7∶2∶1, and roughly comparable to the relative magnitude of the concurrent sea-level pressure trends. These results support the notion that the enhanced wintertime warming over high northern latitudes from 1965 to 2000 was mainly a reflection of unforced variability of the coupled climate system. Some of the simulations exhibit an enhancement of the warming along the Arctic coast, suggestive of exaggerated feedbacks. PMID:22847408

Mechanism of non-appearance of hiatus in Tibetan Plateau.

PubMed

Ma, Jieru; Guan, Xiaodan; Guo, Ruixia; Gan, Zewen; Xie, Yongkun

2017-06-30

In the recent decade, hiatus is the hottest issue in the community of climate change. As the area of great importance, the Tibetan Plateau (TP), however, did not appear to have any warming stoppage in the hiatus period. In fact, the TP showed a continuous warming in the recent decade. To explore why the TP did not show hiatus, we divide the surface air temperature into dynamically-induced temperature (DIT) and radiatively-forced temperature (RFT) by applying the dynamical adjustment method. Our results show that DIT displayed a relatively uniform warming background in the TP, with no obvious correlations with dynamic factors. Meanwhile, as the major contribution to warming, the RFT effect over the TP played the dominant role. The warming role is illustrated using the temperature change between perturbed and control simulation responses to CO 2 or black carbon (BC) forcing via Community Earth System Model (CESM). It shows that an obvious warming in the TP is induced by the CO 2 warming effect, and BC exhibits an amplifying effect on the warming. Therefore, the continuous warming in the TP was a result of uniform DIT warming over a large scale and enhanced RFT warming at a regional scale.

Precipitation and temperature changes in the major Chinese river basins during 1957-2013 and links to sea surface temperature

NASA Astrophysics Data System (ADS)

Tian, Qing; Prange, Matthias; Merkel, Ute

2016-05-01

The variation characteristics of precipitation and temperature in the three major Chinese river basins (Yellow River, Yangtze River and Pearl River) in the period of 1957-2013 were analyzed on an annual and seasonal basis, as well as their links to sea surface temperature (SST) variations in the tropical Pacific and Indian Ocean on both interannual and decadal time scales. Annual mean temperature of the three river basins increased significantly overall since 1957, with an average warming rate of about 0.19 °C/10a, but the warming was characterized by a staircase form with steps around 1987 and 1998. The significant increase of annual mean temperature could mostly be attributed to the remarkable warming trend in spring, autumn and winter. Warming rates in the northern basins were generally much higher than in the southern basins. However, both the annual precipitation and seasonal mean precipitation of the three river basins showed little change in the study area average, but distinct interannual variations since 1957 and clear regional differences. An overall warming-wetting tendency was found in the northwestern and southeastern river basins in 1957-2013, while the central regions tended to become warmer and drier. Results from a Maximum Covariance Analysis (MCA) showed that the interannual variations of seasonal mean precipitation and surface air temperature over the three river basins were both associated with the El Niño-Southern Oscillation (ENSO) since 1957. ENSO SST patterns affected precipitation and surface air temperature variability throughout the year, but with very different response patterns in the different seasons. For instance, temperature in most of the river basins was positively correlated with central-eastern equatorial Pacific SST in winter and spring, but negatively correlated in summer and autumn. On the decadal time scale, the seasonal mean precipitation and surface air temperature variations were strongly associated with the Pacific Quasi-Decadal Oscillation.

Diurnal warming impacts on atmospheric and oceanic evolution during the suppressed phase of the Madden Julian Oscillation

NASA Astrophysics Data System (ADS)

Clayson, C. A.; Roberts, J.

2016-02-01

The Madden-Julian Oscillation (MJO) represents a prominent mode of intraseasonal tropical variability as manifest by coherent large-scale changes in atmospheric circulation, convection, and thermodynamic processes. Its impacts are far-reaching with influences on monsoons, flooding, droughts, and tropical storms. The characteristic timescale of the MJO is positioned in a gap between synoptic forecasting and longer range seasonal to interannual predictions, but has been shown to be dependent on diurnally-varying sea surface temperature (SST). In this work, we leverage a wide suite of satellite products with in situ oceanographic data over the 2002-2012 period to investigate the rectification effects of strong ocean diurnal warming onto the development of intraseasonal SST variability, and whether there a detectable influence on the diurnal cycle of cloud-radiative effects in the suppressed phase of the MJO. Diurnally-varying SST is used as a conditional sampling parameter, along with AIRS/AMSU-A temperature and moisture profiles, surface winds, radiative and turbulent surface fluxes, and precipitation. We use composite daily average atmospheric BL depths, changes in lower-tropospheric stability, and moist static energy to evaluate changes in convective inhibition based on the diurnal variability of surface parcel characteristics due to turbulent heat fluxes, and compare with diurnal changes in cloud-radiative effects and precipitation. Argo floats and ocean modeling experiments are used to examine the upper ocean response. An ensemble of MJO simulations are generated using Argo profiles and satellite-derived surface forcing from which the systematic impacts of diurnal variability on the generation of the intraseasonal SST warming are evaluated. These simulations inform the importance of diurnal variations in surface boundary forcing to upper ocean mixing and the integrated contribution to SST warming over the typical duration of a suppressed phase of the MJO.

Isolating the atmospheric circulation response to Arctic sea-ice loss in the coupled climate system

NASA Astrophysics Data System (ADS)

Kushner, P. J.; Blackport, R.

2016-12-01

In the coupled climate system, projected global warming drives extensive sea-ice loss, but sea-ice loss drives warming that amplifies and can be confounded with the global warming process. This makes it challenging to cleanly attribute the atmospheric circulation response to sea-ice loss within coupled earth-system model (ESM) simulations of greenhouse warming. In this study, many centuries of output from coupled ocean/atmosphere/land/sea-ice ESM simulations driven separately by sea-ice albedo reduction and by projected greenhouse-dominated radiative forcing are combined to cleanly isolate the hemispheric scale response of the circulation to sea-ice loss. To isolate the sea-ice loss signal, a pattern scaling approach is proposed in which the local multidecadal mean atmospheric response is assumed to be separately proportional to the total sea-ice loss and to the total low latitude ocean surface warming. The proposed approach estimates the response to Arctic sea-ice loss with low latitude ocean temperatures fixed and vice versa. The sea-ice response includes a high northern latitude easterly zonal wind response, an equatorward shift of the eddy driven jet, a weakening of the stratospheric polar vortex, an anticyclonic sea level pressure anomaly over coastal Eurasia, a cyclonic sea level pressure anomaly over the North Pacific, and increased wintertime precipitation over the west coast of North America. Many of these responses are opposed by the response to low-latitude surface warming with sea ice fixed. However, both sea-ice loss and low latitude surface warming act in concert to reduce storm track strength throughout the mid and high latitudes. The responses are similar in two related versions of the National Center for Atmospheric Research earth system models, apart from the stratospheric polar vortex response. Evidence is presented that internal variability can easily contaminate the estimates if not enough independent climate states are used to construct them.

Correlated declines in Pacific arctic snow and sea ice cover

USGS Publications Warehouse

Stone, Robert P.; Douglas, David C.; Belchansky, Gennady I.; Drobot, Sheldon

2005-01-01

Simulations of future climate suggest that global warming will reduce Arctic snow and ice cover, resulting in decreased surface albedo (reflectivity). Lowering of the surface albedo leads to further warming by increasing solar absorption at the surface. This phenomenon is referred to as “temperature–albedo feedback.” Anticipation of such a feedback is one reason why scientists look to the Arctic for early indications of global warming. Much of the Arctic has warmed significantly. Northern Hemisphere snow cover has decreased, and sea ice has diminished in area and thickness. As reported in the Arctic Climate Impact Assessment in 2004, the trends are considered to be outside the range of natural variability, implicating global warming as an underlying cause. Changing climatic conditions in the high northern latitudes have influenced biogeochemical cycles on a broad scale. Warming has already affected the sea ice, the tundra, the plants, the animals, and the indigenous populations that depend on them. Changing annual cycles of snow and sea ice also affect sources and sinks of important greenhouse gases (such as carbon dioxide and methane), further complicating feedbacks involving the global budgets of these important constituents. For instance, thawing permafrost increases the extent of tundra wetlands and lakes, releasing greater amounts of methane into the atmosphere. Variable sea ice cover may affect the hemispheric carbon budget by altering the ocean–atmosphere exchange of carbon dioxide. There is growing concern that amplification of global warming in the Arctic will have far-reaching effects on lower latitude climate through these feedback mechanisms. Despite the diverse and convincing observational evidence that the Arctic environment is changing, it remains unclear whether these changes are anthropogenically forced or result from natural variations of the climate system. A better understanding of what controls the seasonal distributions of snow and ice is fundamental to the problem.

The reef-building coral Siderastrea siderea exhibits parabolic responses to ocean acidification and warming.

PubMed

Castillo, Karl D; Ries, Justin B; Bruno, John F; Westfield, Isaac T

2014-12-22

Anthropogenic increases in atmospheric CO2 over this century are predicted to cause global average surface ocean pH to decline by 0.1-0.3 pH units and sea surface temperature to increase by 1-4°C. We conducted controlled laboratory experiments to investigate the impacts of CO2-induced ocean acidification (pCO2 = 324, 477, 604, 2553 µatm) and warming (25, 28, 32°C) on the calcification rate of the zooxanthellate scleractinian coral Siderastrea siderea, a widespread, abundant and keystone reef-builder in the Caribbean Sea. We show that both acidification and warming cause a parabolic response in the calcification rate within this coral species. Moderate increases in pCO2 and warming, relative to near-present-day values, enhanced coral calcification, with calcification rates declining under the highest pCO2 and thermal conditions. Equivalent responses to acidification and warming were exhibited by colonies across reef zones and the parabolic nature of the corals' response to these stressors was evident across all three of the experiment's 30-day observational intervals. Furthermore, the warming projected by the Intergovernmental Panel on Climate Change for the end of the twenty-first century caused a fivefold decrease in the rate of coral calcification, while the acidification projected for the same interval had no statistically significant impact on the calcification rate-suggesting that ocean warming poses a more immediate threat than acidification for this important coral species.

The reef-building coral Siderastrea siderea exhibits parabolic responses to ocean acidification and warming

PubMed Central

Castillo, Karl D.; Ries, Justin B.; Bruno, John F.; Westfield, Isaac T.

2014-01-01

Anthropogenic increases in atmospheric CO2 over this century are predicted to cause global average surface ocean pH to decline by 0.1–0.3 pH units and sea surface temperature to increase by 1–4°C. We conducted controlled laboratory experiments to investigate the impacts of CO2-induced ocean acidification (pCO2 = 324, 477, 604, 2553 µatm) and warming (25, 28, 32°C) on the calcification rate of the zooxanthellate scleractinian coral Siderastrea siderea, a widespread, abundant and keystone reef-builder in the Caribbean Sea. We show that both acidification and warming cause a parabolic response in the calcification rate within this coral species. Moderate increases in pCO2 and warming, relative to near-present-day values, enhanced coral calcification, with calcification rates declining under the highest pCO2 and thermal conditions. Equivalent responses to acidification and warming were exhibited by colonies across reef zones and the parabolic nature of the corals' response to these stressors was evident across all three of the experiment's 30-day observational intervals. Furthermore, the warming projected by the Intergovernmental Panel on Climate Change for the end of the twenty-first century caused a fivefold decrease in the rate of coral calcification, while the acidification projected for the same interval had no statistically significant impact on the calcification rate—suggesting that ocean warming poses a more immediate threat than acidification for this important coral species. PMID:25377455

How does the Redi parameter for mesoscale mixing impact global climate in an Earth System Model?

NASA Astrophysics Data System (ADS)

Pradal, Marie-Aude; Gnanadesikan, Anand

2014-09-01

A coupled climate model is used to examine the impact of an increase in the mixing due to mesoscale eddies on the global climate system. A sixfold increase in the Redi mixing coefficient ARedi, which is within the admissible range of variation, has the overall effect of warming the global-mean surface air and sea surface temperatures by more than 1°C. Locally, sea surface temperatures increase by up to 7°C in the North Pacific and by up to 4°C in the Southern Ocean, with corresponding impacts on the ice concentration and ice extent in polar regions. However, it is not clear that the changes in heat transport from tropics to poles associated with changing this coefficient are primarily responsible for these changes. We found that the changes in the transport of heat are often much smaller than changes in long-wave trapping and short-wave absorption. Additionally, changes in the advective and diffusive transport of heat toward the poles often oppose each other. However, we note that the poleward transport of salt increases near the surface as ARedi increases. We suggest a causal chain in which enhanced eddy stirring leads to increased high-latitude surface salinity reducing salt stratification and water column stability and enhancing convection, triggering two feedback loops. In one, deeper convection prevents sea ice formation, which decreases albedo, which increases SW absorption, further increasing SST and decreasing sea ice formation. In the other, increased SST and reduced sea ice allow for more water vapor in the atmosphere, trapping long-wave radiation. Destratifying the polar regions is thus a potential way in which changes in ocean circulation might warm the planet.

Vascular plant abundance and diversity in an alpine heath under observed and simulated global change

PubMed Central

Alatalo, Juha M.; Little, Chelsea J.; Jägerbrand, Annika K.; Molau, Ulf

2015-01-01

Global change is predicted to cause shifts in species distributions and biodiversity in arctic tundra. We applied factorial warming and nutrient manipulation to a nutrient and species poor alpine/arctic heath community for seven years. Vascular plant abundance in control plots increased by 31%. There were also notable changes in cover in the nutrient and combined nutrient and warming treatments, with deciduous and evergreen shrubs declining, grasses overgrowing these plots. Sedge abundance initially increased significantly with nutrient amendment and then declined, going below initial values in the combined nutrient and warming treatment. Nutrient addition resulted in a change in dominance hierarchy from deciduous shrubs to grasses. We found significant declines in vascular plant diversity and evenness in the warming treatment and a decline in diversity in the combined warming and nutrient addition treatment, while nutrient addition caused a decline in species richness. The results give some experimental support that species poor plant communities with low diversity may be more vulnerable to loss of species diversity than communities with higher initial diversity. The projected increase in nutrient deposition and warming may therefore have negative impacts on ecosystem processes, functioning and services due to loss of species diversity in an already impoverished environment. PMID:25950370

Tropical North Atlantic subsurface warming events as a fingerprint for AMOC variability during Marine Isotope Stage 3

NASA Astrophysics Data System (ADS)

Parker, Andrew O.; Schmidt, Matthew W.; Chang, Ping

2015-11-01

The role of Atlantic Meridional Overturning Circulation (AMOC) as the driver of Dansgaard-Oeschger (DO) variability that characterized Marine Isotope Stage 3 (MIS 3) has long been hypothesized. Although there is ample proxy evidence suggesting that DO events were robust features of glacial climate, there is little data supporting a link with AMOC. Recently, modeling studies and subsurface temperature reconstructions have suggested that subsurface warming across the tropical North Atlantic can be used to fingerprint a weakened AMOC during the deglacial because a reduction in the strength of the western boundary current allows warm salinity maximum water of the subtropical gyre to enter the deep tropics. To determine if AMOC variability played a role during the DO cycles of MIS 3, we present new, high-resolution Mg/Ca and δ18O records spanning 24-52 kyr from the near-surface dwelling planktonic foraminifera Globigerinoides ruber and the lower thermocline dwelling planktonic foraminifera Globorotalia truncatulinoides in Southern Caribbean core VM12-107 (11.33°N, 66.63°W, 1079 m depth). Our subsurface Mg/Ca record reveals abrupt increases in Mg/Ca ratios (the largest equal to a 4°C warming) during the interstadial-stadial transition of most DO events during this period. This change is consistent with reconstructions of subsurface warming events associated with cold events across the deglacial using the same core. Additionally, our data support the conclusion reached by a recently published study from the Florida Straits that AMOC did not undergo significant reductions during Heinrich events 2 and 3. This record presents some of the first high-resolution marine sediment derived evidence for variable AMOC during MIS 3.

A spurious warming trend in the NMME equatorial Pacific SST hindcasts

NASA Astrophysics Data System (ADS)

Shin, Chul-Su; Huang, Bohua

2017-06-01

Using seasonal hindcasts of six different models participating in the North American Multimodel Ensemble project, the trend of the predicted sea surface temperature (SST) in the tropical Pacific for 1982-2014 at each lead month and its temporal evolution with respect to the lead month are investigated for all individual models. Since the coupled models are initialized with the observed ocean, atmosphere, land states from observation-based reanalysis, some of them using their own data assimilation process, one would expect that the observed SST trend is reasonably well captured in their seasonal predictions. However, although the observed SST features a weak-cooling trend for the 33-year period with La Niña-like spatial pattern in the tropical central-eastern Pacific all year round, it is demonstrated that all models having a time-dependent realistic concentration of greenhouse gases (GHG) display a warming trend in the equatorial Pacific that amplifies as the lead-time increases. In addition, these models' behaviors are nearly independent of the starting month of the hindcasts although the growth rates of the trend vary with the lead month. This key characteristic of the forecasted SST trend in the equatorial Pacific is also identified in the NCAR CCSM3 hindcasts that have the GHG concentration for a fixed year. This suggests that a global warming forcing may not play a significant role in generating the spurious warming trend of the coupled models' SST hindcasts in the tropical Pacific. This model SST trend in the tropical central-eastern Pacific, which is opposite to the observed one, causes a developing El Niño-like warming bias in the forecasted SST with its peak in boreal winter. Its implications for seasonal prediction are discussed.

Meteorological Drivers of West Antarctic Ice Sheet and Ice Shelf Surface Melt

NASA Astrophysics Data System (ADS)

Scott, R. C.; Nicolas, J. P.; Bromwich, D. H.; Norris, J. R.; Lubin, D.

2017-12-01

We identify synoptic patterns and surface energy balance components driving warming and surface melting on the West Antarctic Ice Sheet (WAIS) and ice shelves using reanalysis and satellite remote sensing data from 1973-present. We have developed a synoptic climatology of atmospheric circulation patterns during the summer melt season using k-means cluster and composite analysis of daily 700-mb geopotential height and near-surface air temperature and wind fields from the ECMWF ERA-Interim reanalysis. Surface melt occurrence is detected in satellite passive microwave brightness temperature observations (K-band, horizontal polarization) beginning with the NASA Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR) and continuing with its more familiar descendants SMMR, SSM/I and SSMIS. To diagnose synoptic precursors and physical processes driving surface melt we combine the circulation climatology and multi-decadal records of cloud cover with surface radiative fluxes from the Extended AVHRR Polar Pathfinder (APP-x) project. We identify three distinct modes of regional summer West Antarctic warming since 1979 involving anomalous ridging over West Antarctica (WA) and the Amundsen Sea (AS). During the 1970s, ESMR data reveal four extensive melt events on the Ross Sea sector of the WAIS also linked to AS blocking. We therefore define an Amundsen Sea Blocking Index (ASBI). The ASBI and synoptic circulation pattern occurrence frequencies are correlated with the tropical Pacific (ENSO) and high latitude Southern Annular Mode (SAM) indices and the West Antarctic melt index. Surface melt in WA is favored by enhanced downwelling infrared and turbulent sensible heat fluxes associated with intrusions of warm, moist marine air. Consistent with recent findings from the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE), marine advection to the Ross sector is favored by El Niño conditions in the tropical Pacific and a negative SAM. We also find that El Niño-related blocking favors warming and melting on the marine-based ice streams draining from Wilkes Basin, East Antarctica.

Model-based assessment of the role of human-induced climate change in the 2005 Caribbean coral bleaching event.

PubMed

Donner, Simon D; Knutson, Thomas R; Oppenheimer, Michael

2007-03-27

Episodes of mass coral bleaching around the world in recent decades have been attributed to periods of anomalously warm ocean temperatures. In 2005, the sea surface temperature (SST) anomaly in the tropical North Atlantic that may have contributed to the strong hurricane season caused widespread coral bleaching in the Eastern Caribbean. Here, we use two global climate models to evaluate the contribution of natural climate variability and anthropogenic forcing to the thermal stress that caused the 2005 coral bleaching event. Historical temperature data and simulations for the 1870-2000 period show that the observed warming in the region is unlikely to be due to unforced climate variability alone. Simulation of background climate variability suggests that anthropogenic warming may have increased the probability of occurrence of significant thermal stress events for corals in this region by an order of magnitude. Under scenarios of future greenhouse gas emissions, mass coral bleaching in the Eastern Caribbean may become a biannual event in 20-30 years. However, if corals and their symbionts can adapt by 1-1.5 degrees C, such mass bleaching events may not begin to recur at potentially harmful intervals until the latter half of the century. The delay could enable more time to alter the path of greenhouse gas emissions, although long-term "committed warming" even after stabilization of atmospheric CO(2) levels may still represent an additional long-term threat to corals.

Biological consequences of earlier snowmelt from desert dust deposition in alpine landscapes.

PubMed

Steltzer, Heidi; Landry, Chris; Painter, Thomas H; Anderson, Justin; Ayres, Edward

2009-07-14

Dust deposition to mountain snow cover, which has increased since the late 19(th) century, accelerates the rate of snowmelt by increasing the solar radiation absorbed by the snowpack. Snowmelt occurs earlier, but is decoupled from seasonal warming. Climate warming advances the timing of snowmelt and early season phenological events (e.g., the onset of greening and flowering); however, earlier snowmelt without warmer temperatures may have a different effect on phenology. Here, we report the results of a set of snowmelt manipulations in which radiation-absorbing fabric and the addition and removal of dust from the surface of the snowpack advanced or delayed snowmelt in the alpine tundra. These changes in the timing of snowmelt were superimposed on a system where the timing of snowmelt varies with topography and has been affected by increased dust loading. At the community level, phenology exhibited a threshold response to the timing of snowmelt. Greening and flowering were delayed before seasonal warming, after which there was a linear relationship between the date of snowmelt and the timing of phenological events. Consequently, the effects of earlier snowmelt on phenology differed in relation to topography, which resulted in increasing synchronicity in phenology across the alpine landscape with increasingly earlier snowmelt. The consequences of earlier snowmelt from increased dust deposition differ from climate warming and include delayed phenology, leading to synchronized growth and flowering across the landscape and the opportunity for altered species interactions, landscape-scale gene flow via pollination, and nutrient cycling.

Contrail Coverage Over the USA Derived from NOAA and EOS Satellite Data

NASA Technical Reports Server (NTRS)

Palikonda, Rabindra; Minnis, Patrick; Duda, David P.

2004-01-01

Contrails, like natural cirrus clouds, can cause a warming of the Earth-atmospheric system by absorbing longwave radiation from the surface and lower troposphere and radiating additional radiation back to the surface. They can also produce some cooling of the surface during the daytime by reflecting some sunlight back to space. Recently, Minnis et al. (2004) determined from surface observations of cirrus cloud cover that the overall impact appears to be a warming that is consistent with theoretical calculations, at least over the United States of America (USA) and surrounding areas. This finding highlights the need to better understand the formation and persistence of contrails and their radiative properties. To better assess the climatic impact of contrails, it is essential to determine the variability of the contrail microphysical properties, their impact on the atmospheric radiation budget, and their relationship to the atmospheric state. To that end, this paper continues the analyses of Advanced Very High Resolution Radiometer (AVHRR) data from the NOAA-15 (N15), NOAA-16 (N16), and NOAA-17 (N17) satellites, Moderate Resolution Imaging Spectroradiometer (MODIS) data from the Terra and Aqua satellites. The combination of these satellites provides a relatively comprehensive coverage of the daily cycle of air traffic. Thus, it should be possible to use these data to help understand the impact of air traffic on the upper tropospheric humidity during the day as well as determine the local-time variability of contrail coverage. The results will be valuable for developing models of contrail effects and methods for mitigating the impact of aviation on climate.

Divergent surface and total soil moisture projections under global warming

USGS Publications Warehouse

Berg, Alexis; Sheffield, Justin; Milly, Paul C.D.

2017-01-01

Land aridity has been projected to increase with global warming. Such projections are mostly based on off-line aridity and drought metrics applied to climate model outputs but also are supported by climate-model projections of decreased surface soil moisture. Here we comprehensively analyze soil moisture projections from the Coupled Model Intercomparison Project phase 5, including surface, total, and layer-by-layer soil moisture. We identify a robust vertical gradient of projected mean soil moisture changes, with more negative changes near the surface. Some regions of the northern middle to high latitudes exhibit negative annual surface changes but positive total changes. We interpret this behavior in the context of seasonal changes in the surface water budget. This vertical pattern implies that the extensive drying predicted by off-line drought metrics, while consistent with the projected decline in surface soil moisture, will tend to overestimate (negatively) changes in total soil water availability.

Warm tropical ocean surface and global anoxia during the mid-Cretaceous period.

PubMed

Wilson, P A; Norris, R D

2001-07-26

The middle of the Cretaceous period (about 120 to 80 Myr ago) was a time of unusually warm polar temperatures, repeated reef-drowning in the tropics and a series of oceanic anoxic events (OAEs) that promoted both the widespread deposition of organic-carbon-rich marine sediments and high biological turnover. The cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide. In contrast, there is no consensus on the climatic causes and effects of the OAEs, with both high biological productivity and ocean 'stagnation' being invoked as the cause of ocean anoxia. Here we show, using stable isotope records from multiple species of well-preserved foraminifera, that the thermal structure of surface waters in the western tropical Atlantic Ocean underwent pronounced variability about 100 Myr ago, with maximum sea surface temperatures 3-5 degrees C warmer than today. This variability culminated in a collapse of upper-ocean stratification during OAE-1d (the 'Breistroffer' event), a globally significant period of organic-carbon burial that we show to have fundamental, stratigraphically valuable, geochemical similarities to the main OAEs of the Mesozoic era. Our records are consistent with greenhouse forcing being responsible for the warm temperatures, but are inconsistent both with explanations for OAEs based on ocean stagnation, and with the traditional view (reviewed in ref. 12) that past warm periods were more stable than today's climate.

Influence of warm air-drying on enamel bond strength and surface free-energy of self-etch adhesives.

PubMed

Shiratsuchi, Koji; Tsujimoto, Akimasa; Takamizawa, Toshiki; Furuichi, Tetsuya; Tsubota, Keishi; Kurokawa, Hiroyasu; Miyazaki, Masashi

2013-08-01

We examined the effect of warm air-drying on the enamel bond strengths and the surface free-energy of three single-step self-etch adhesives. Bovine mandibular incisors were mounted in self-curing resin and then wet ground with #600 silicon carbide (SiC) paper. The adhesives were applied according to the instructions of the respective manufacturers and then dried in a stream of normal (23°C) or warm (37°C) air for 5, 10, and 20 s. After visible-light irradiation of the adhesives, resin composites were condensed into a mold and polymerized. Ten samples per test group were stored in distilled water at 37°C for 24 h and then the bond strengths were measured. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths varied according to the air-drying time and ranged from 15.8 to 19.1 MPa. The trends for the bond strengths were different among the materials. The value of the γS⁺ component increased slightly when drying was performed with a stream of warm air, whereas that of the γS⁻ component decreased significantly. These data suggest that warm air-drying is essential to obtain adequate enamel bond strengths, although increasing the drying time did not significantly influence the bond strength. © 2013 Eur J Oral Sci.

CMIP5 Historical Simulations (1850-2012) with GISS ModelE2

NASA Technical Reports Server (NTRS)

Miller, Ronald Lindsay; Schmidt, Gavin A.; Nazarenko, Larissa S.; Tausnev, Nick; Bauer, Susanne E.; DelGenio, Anthony D.; Kelley, Max; Lo, Ken K.; Ruedy, Reto; Shindell, Drew T.;

Understanding the causes of recent warming of mediterranean waters. How much could be attributed to climate change?

PubMed

Macias, Diego; Garcia-Gorriz, Elisa; Stips, Adolf

2013-01-01

During the past two decades, Mediterranean waters have been warming at a rather high rate resulting in scientific and social concern. This warming trend is observed in satellite data, field data and model simulations, and affects both surface and deep waters throughout the Mediterranean basin. However, the warming rate is regionally different and seems to change with time, which has led to the question of what causes underlie the observed trends. Here, we analyze available satellite information on sea surface temperature (SST) from the last 25 years using spectral techniques and find that more than half of the warming tendency during this period is due to a non-linear, wave-like tendency. Using a state of the art hydrodynamic model, we perform a hindcast simulation and obtain the simulated SST evolution of the Mediterranean basin for the last 52 years. These SST results show a clear sinusoidal tendency that follows the Atlantic Multidecadal Oscillation (AMO) during the simulation period. Our results reveal that 58% of recent warming in Mediterranean waters could be attributed to this AMO-like oscillation, being anthropogenic-induced climate change only responsible for 42% of total trend. The observed acceleration of water warming during the 1990s therefore appears to be caused by a superimposition of anthropogenic-induced warming with the positive phase of the AMO, while the recent slowdown of this tendency is likely due to a shift in the AMO phase. It has been proposed that this change in the AMO phase will mask the effect of global warming in the forthcoming decades, and our results indicate that the same could also be applicable to the Mediterranean Sea. Henceforth, natural multidecadal temperature oscillations should be taken into account to avoid underestimation of the anthropogenic-induced warming of the Mediterranean basin in the future.

A study of the dynamics of droughts in Northern Brazil: Observations, theory, and numerical experiments with a global atmospheric circulation model

NASA Technical Reports Server (NTRS)

Shukla, J.; Moura, A. D.

1980-01-01

The monthly mean sea surface temperature anomalies over tropical Altantic and rainfall anomalies over two selected stations for 25 years (1948-1972) were examined. It is found that the most severe drought events are associated with the simultaneous occurrence of warm sea surface temperature anomalies over north and cold sea surface temperature anomalies over south tropical Atlantic. Simultaneous occurrences of warm sea surface temperature anomaly at 15 deg N, 45 deg W and cold sea surface temperature anomaly at 15 deg S, 5 deg W were always associated with negative anomalies of rainfall, and vice versa. A simple primitive equation model is used to calculate the frictionally controlled and thermally driven circulation due to a prescribed heating function in a resting atmosphere.

Observing changes in atmospheric heat content

NASA Astrophysics Data System (ADS)

Balcerak, Ernie

2011-10-01

Globally, air temperatures near the surface over land have been rising in recent decades, and this has been presented as solid evidence of global warming. However, some scientists have argued that total heat content (energy), rather than temperature, should be used as a metric of warming trends. Surface air temperature is only one component of the energy content of the surface atmosphere—kinetic energy and latent heat also contribute. Peterson et al. present the first study to use observational data to estimate global changes in surface energy of the atmosphere over time. They include temperature, kinetic energy, and latent heat in their analysis. The authors found that total global surface atmospheric energy and heat content have increased since the 1970s, even though kinetic energy decreased slightly and in some regions latent heat declined while temperature increased.

Dynamically driven super C-C intensification of the tropical hydrological cycle

NASA Astrophysics Data System (ADS)

Hakuba, Maria Z.; Stephens, Graeme L.; Kahn, Brian; Yue, Qing; Lebsock, Matthew D.; Hristova-Veleva, Svetla; Rapp, Anita D.; Stubenrauch, Claudia

2017-04-01

Improving our understanding of the hydrological cycle and the way it responds to a warming world represents one of the greatest challenges in current climate research. We expect global mean precipitation to increase by about 2% per degree of surface warming, constrained by the atmospheric energy budget on the one hand and the availability of atmospheric water vapor (Clausius-Clapeyron) on the other. Regional changes in precipitation pattern and intensity are less well known and often described by the 'wet gets wetter and dry gets drier' paradigm. The currently wettest region of our planet is characterized by organized deep tropical convection over the equatorial oceans and referred to as the Inter-Tropical Convergence Zone (ITCZ). To quantify potential changes of the tropical water cycle in a warmer climate, we have analyzed a great amount of independent observational datasets collected over multiple decades. With this we reveal a strong, positive feedback on tropical convection in the Pacific associated with the short-term climate variations of the El Niño/Southern Oscillation (ENSO). This dynamical feedback is in addition to the established Bjerknes (positive) and surface heat flux (negative) feedbacks and is a result of coupled dynamical-radiative-convective processes that produce observed responses in precipitation and cloud amount far beyond those expected from the Clausius-Clapeyron (CC) response alone. We have indication that this dynamical feedback is driven by differential atmospheric heating rates in the convective regions (heating) and adjacent regions to the south, north and west (cooling) leading to inflow that feeds the convectively active zones. This evidence is supported by analysis of observed surface wind divergence and vertical motion from reanalysis. While super-CC responses to global warming have been examined with respect to local and short-term weather events, this study provides the first observational evidence of a much larger scale response on seasonal and longer time scales.

El Ni?o Pumping Up, Warm Kelvin Wave Surges Toward South America

NASA Image and Video Library

2009-11-12

ElNi?o is experiencing a late-fall resurgence. Sea-level height data from the NASA/European Ocean Surface Topography Mission/Jason-2 oceanography satellite show the equatorial Pacific has triggered a wave of warm water, known as a Kelvin wave.

El Niño Surges; Warm Kelvin Wave Headed for South America

NASA Image and Video Library

2009-12-17

The most recent sea-level height data from the NASA/European Ocean Surface Topography Mission/Jason-2 oceanography satellite show the continued eastward progression of a strong wave of warm water, known as a Kelvin wave, now approaching South America.

Western tropical Pacific multidecadal variability forced by the Atlantic multidecadal oscillation

NASA Astrophysics Data System (ADS)

Kucharski, F.; Sun, C.; Li, J.; Jin, F. F.; Kang, I. S.; Ding, R.

2017-12-01

Observational analysis suggests that the western tropical Pacific (WTP) sea surface temperature (SST) shows predominant variability over multidecadal time scales, which is unlikely to be explained by the Interdecadal Pacific Oscillation. Here we show that this variability is largely explained by the remote Atlantic multidecadal oscillation (AMO). A suite of Atlantic Pacemaker experiments successfully reproduces the WTP multidecadal variability and the AMO-WTP SST connection. The AMO warm SST anomaly generates an atmospheric teleconnection to the North Pacific, which weakens the Aleutian low and subtropical North Pacific westerlies. The wind changes induce a subtropical North Pacific SST warming through wind-evaporation-SST effect, and in response to this warming, the surface winds converge towards the subtropical North Pacific from the tropics, leading to anomalous cyclonic circulation and low pressure over the WTP region. The warm SST anomaly further develops due to the SST-sea level pressure-cloud-longwave radiation positive feedback. Our findings suggest that the Atlantic Ocean acts as a key pacemaker for the western Pacific decadal climate variability.

Effects of Global Warming on Vibrio Ecology.

PubMed

Vezzulli, Luigi; Pezzati, Elisabetta; Brettar, Ingrid; Höfle, Manfred; Pruzzo, Carla

2015-06-01

Vibrio-related infections are increasing worldwide both in humans and aquatic animals. Rise in global sea surface temperature (SST), which is approximately 1 °C higher now than 140 years ago and is one of the primary physical impacts of global warming, has been linked to such increases. In this chapter, major known effects of increasing SST on the biology and ecology of vibrios are described. They include the effects on bacterial growth rate, both in the field and in laboratory, culturability, expression of pathogenicity traits, and interactions with aquatic organisms and abiotic surfaces. Special emphasis is given to the effect of ocean warming on Vibrio interactions with zooplankters, which represent one of the most important aquatic reservoirs for these bacteria. The reported findings highlight the biocomplexity of the interactions between vibrios and their natural environment in a climate change scenario, posing the need for interdisciplinary studies to properly understand the connection between ocean warming and persistence and spread of vibrios in sea waters and the epidemiology of the diseases they cause.

Western tropical Pacific multidecadal variability forced by the Atlantic multidecadal oscillation

PubMed Central

Sun, Cheng; Kucharski, Fred; Li, Jianping; Jin, Fei-Fei; Kang, In-Sik; Ding, Ruiqiang

2017-01-01

Observational analysis suggests that the western tropical Pacific (WTP) sea surface temperature (SST) shows predominant variability over multidecadal time scales, which is unlikely to be explained by the Interdecadal Pacific Oscillation. Here we show that this variability is largely explained by the remote Atlantic multidecadal oscillation (AMO). A suite of Atlantic Pacemaker experiments successfully reproduces the WTP multidecadal variability and the AMO–WTP SST connection. The AMO warm SST anomaly generates an atmospheric teleconnection to the North Pacific, which weakens the Aleutian low and subtropical North Pacific westerlies. The wind changes induce a subtropical North Pacific SST warming through wind–evaporation–SST effect, and in response to this warming, the surface winds converge towards the subtropical North Pacific from the tropics, leading to anomalous cyclonic circulation and low pressure over the WTP region. The warm SST anomaly further develops due to the SST–sea level pressure–cloud–longwave radiation positive feedback. Our findings suggest that the Atlantic Ocean acts as a key pacemaker for the western Pacific decadal climate variability. PMID:28685765

Effect of equatorial line nodes on the upper critical field and London penetration depth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kogan, V G; Prozorov, R

2014-09-01

The upper critical field Hc2 and its anisotropy are calculated for order parameters with line nodes at the equators, kz=0, of the Fermi surface of uniaxial superconductors. It is shown that characteristic features found in Fe-based materials (a nearly linear Hc2(T) in a broad T domain, a low and increasing on warming anisotropy γH=Hc2,ab/Hc2,c) can be caused by competing effects of the equatorial nodes and of the Fermi surface anisotropy. For certain material parameters, γH(T)-1 may change sign upon warming, in agreement with the recorded behavior of FeTeS systems. It is also shown that the anisotropy of the penetration depthmore » γλ=λc/λab decreases upon warming to reach γH at Tc, in agreement with data available. For some materials γλ(T) may change upon warming, from γλ>1 at low Ts to γλ<1 at high Ts.« less

Linear dependence of surface expansion speed on initial plasma temperature in warm dense matter

DOE PAGES

Bang, Woosuk; Albright, Brian James; Bradley, Paul Andrew; ...

2016-07-12

Recent progress in laser-driven quasi-monoenergetic ion beams enabled the production of uniformly heated warm dense matter. Matter heated rapidly with this technique is under extreme temperatures and pressures, and promptly expands outward. While the expansion speed of an ideal plasma is known to have a square-root dependence on temperature, computer simulations presented here show a linear dependence of expansion speed on initial plasma temperature in the warm dense matter regime. The expansion of uniformly heated 1–100 eV solid density gold foils was modeled with the RAGE radiation-hydrodynamics code, and the average surface expansion speed was found to increase linearly withmore » temperature. The origin of this linear dependence is explained by comparing predictions from the SESAME equation-of-state tables with those from the ideal gas equation-of-state. In conclusion, these simulations offer useful insight into the expansion of warm dense matter and motivate the application of optical shadowgraphy for temperature measurement.« less

Western tropical Pacific multidecadal variability forced by the Atlantic multidecadal oscillation

NASA Astrophysics Data System (ADS)

Sun, Cheng; Kucharski, Fred; Li, Jianping; Jin, Fei-Fei; Kang, In-Sik; Ding, Ruiqiang

2017-07-01

Observational analysis suggests that the western tropical Pacific (WTP) sea surface temperature (SST) shows predominant variability over multidecadal time scales, which is unlikely to be explained by the Interdecadal Pacific Oscillation. Here we show that this variability is largely explained by the remote Atlantic multidecadal oscillation (AMO). A suite of Atlantic Pacemaker experiments successfully reproduces the WTP multidecadal variability and the AMO-WTP SST connection. The AMO warm SST anomaly generates an atmospheric teleconnection to the North Pacific, which weakens the Aleutian low and subtropical North Pacific westerlies. The wind changes induce a subtropical North Pacific SST warming through wind-evaporation-SST effect, and in response to this warming, the surface winds converge towards the subtropical North Pacific from the tropics, leading to anomalous cyclonic circulation and low pressure over the WTP region. The warm SST anomaly further develops due to the SST-sea level pressure-cloud-longwave radiation positive feedback. Our findings suggest that the Atlantic Ocean acts as a key pacemaker for the western Pacific decadal climate variability.

Global temperature change

PubMed Central

Hansen, James; Sato, Makiko; Ruedy, Reto; Lo, Ken; Lea, David W.; Medina-Elizade, Martin

2006-01-01

Global surface temperature has increased ≈0.2°C per decade in the past 30 years, similar to the warming rate predicted in the 1980s in initial global climate model simulations with transient greenhouse gas changes. Warming is larger in the Western Equatorial Pacific than in the Eastern Equatorial Pacific over the past century, and we suggest that the increased West–East temperature gradient may have increased the likelihood of strong El Niños, such as those of 1983 and 1998. Comparison of measured sea surface temperatures in the Western Pacific with paleoclimate data suggests that this critical ocean region, and probably the planet as a whole, is approximately as warm now as at the Holocene maximum and within ≈1°C of the maximum temperature of the past million years. We conclude that global warming of more than ≈1°C, relative to 2000, will constitute “dangerous” climate change as judged from likely effects on sea level and extermination of species. PMID:17001018

Tracking the Subsurface Signal of Decadal Climate Warming to Quantify Vertical Groundwater Flow Rates

NASA Astrophysics Data System (ADS)

Bense, V. F.; Kurylyk, B. L.

2017-12-01

Sustained ground surface warming on a decadal time scale leads to an inversion of thermal gradients in the upper tens of meters. The magnitude and direction of vertical groundwater flow should influence the propagation of this warming signal, but direct field observations of this phenomenon are rare. Comparison of temperature-depth profiles in boreholes in the Veluwe area, Netherlands, collected in 1978-1982 and 2016 provided such direct measurement. We used these repeated profiles to track the downward propagation rate of the depth at which the thermal gradient is zero. Numerical modeling of the migration of this thermal gradient "inflection point" yielded estimates of downward groundwater flow rates (0-0.24 m a-1) that generally concurred with known hydrogeological conditions in the area. We conclude that analysis of inflection point depths in temperature-depth profiles impacted by surface warming provides a largely untapped opportunity to inform sustainable groundwater management plans that rely on accurate estimates of long-term vertical groundwater fluxes.

Integrated surface/subsurface permafrost thermal hydrology: Model formulation and proof-of-concept simulations

DOE PAGES

Painter, Scott L.; Coon, Ethan T.; Atchley, Adam L.; ...

2016-08-11

The need to understand potential climate impacts and feedbacks in Arctic regions has prompted recent interest in modeling of permafrost dynamics in a warming climate. A new fine-scale integrated surface/subsurface thermal hydrology modeling capability is described and demonstrated in proof-of-concept simulations. The new modeling capability combines a surface energy balance model with recently developed three-dimensional subsurface thermal hydrology models and new models for nonisothermal surface water flows and snow distribution in the microtopography. Surface water flows are modeled using the diffusion wave equation extended to include energy transport and phase change of ponded water. Variation of snow depth in themore » microtopography, physically the result of wind scour, is also modeled heuristically with a diffusion wave equation. The multiple surface and subsurface processes are implemented by leveraging highly parallel community software. Fully integrated thermal hydrology simulations on the tilted open book catchment, an important test case for integrated surface/subsurface flow modeling, are presented. Fine-scale 100-year projections of the integrated permafrost thermal hydrological system on an ice wedge polygon at Barrow Alaska in a warming climate are also presented. Finally, these simulations demonstrate the feasibility of microtopography-resolving, process-rich simulations as a tool to help understand possible future evolution of the carbon-rich Arctic tundra in a warming climate.« less