Earth System Dynamics Discussions最新文献

{"title":"The Half-order Energy Balance Equation, Part 1: The homogeneous HEBE and long memories","authors":"S. Lovejoy","doi":"10.5194/esd-2020-12","DOIUrl":"https://doi.org/10.5194/esd-2020-12","url":null,"abstract":"Abstract. The original Budyko–Sellers type 1-D energy balance models (EBMs) consider the Earth system averaged over long times and applies the continuum mechanics heat equation. When these and the more phenomenological zero (horizontal) – dimensional box models are extended to include time varying anomalies, they have a key weakness: neither model explicitly nor realistically treats the surface radiative – conductive surface boundary condition that is necessary for a correct treatment of energy storage. In this first of a two part series, we apply standard Laplace and Fourier techniques to the continuum mechanics heat equation, solving it with the correct radiative – conductive BC's obtaining an equation directly for the surface temperature anomalies in terms of the anomalous forcing. Although classical, this equation is half – not integer – ordered: the Half - ordered Energy Balance Equation (HEBE). A quite general consequence is that although Newton's law of cooling holds, that the heat flux across surfaces is proportional to a half (not first) ordered derivative of the surface temperature. This implies that the surface heat flux has a long memory, that it depends on the entire previous history of the forcing, the relationship is no longer instantaneous. We then consider the case where the Earth is periodically forced. The classical case is diurnal heat forcing; we extend this to annual conductive – radiative forcing and show that the surface thermal impedance is a complex valued quantity equal to the (complex) climate sensitivity. Using a simple semi-empirical model, we show how this can account for the phase lag between the summer maximum forcing and maximum surface temperature Earth response. In part II, we extend all these results to spatially inhomogeneous forcing and to the full horizontally inhomogeneous problem with spatially varying specific heats, diffusivities, advection velocities, climate sensitivities. We consider the consequences for macroweather forecasting and climate projections.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"138 1","pages":"1-36"},"PeriodicalIF":0.0,"publicationDate":"2020-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73523310","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Winter hydrometeorological extreme events modulated by large-scale atmospheric circulation in southern Ontario","authors":"O. Champagne, M. Leduc, P. Coulibaly, M. A. Arain","doi":"10.5194/ESD-11-301-2020","DOIUrl":"https://doi.org/10.5194/ESD-11-301-2020","url":null,"abstract":"Abstract. Extreme events are widely studied across the world because of their major implications for many aspects of society and especially floods. These events are generally studied in terms of precipitation or temperature extreme indices that are often not adapted for regions affected by floods caused by snowmelt. The rain on snow index has been widely used, but it neglects rain-only events which are expected to be more frequent in the future. In this study, we identified a new winter compound index and assessed how large-scale atmospheric circulation controls the past and future evolution of these events in the Great Lakes region. The future evolution of this index was projected using temperature and precipitation\u0000from the Canadian Regional Climate Model large ensemble (CRCM5-LE). These\u0000climate data were used as input in Precipitation Runoff Modelling System (PRMS) hydrological model to simulate the\u0000future evolution of high flows in three watersheds in southern Ontario. We\u0000also used five recurrent large-scale atmospheric circulation patterns in\u0000north-eastern North America and identified how they control the past and\u0000future variability of the newly created index and high flows. The results\u0000show that daily precipitation higher than 10 mm and temperature higher than 5  ∘ C were necessary historical conditions to produce high flows in these three watersheds. In the historical period, the occurrences of these heavy rain and warm events as well as high flows were associated with two main patterns characterized by high Z500  anomalies centred on eastern Great Lakes (HP regime) and the Atlantic Ocean (South regime). These hydrometeorological extreme events will still be associated with the same atmospheric patterns in the near future. The future evolution of the index will be modulated by the internal variability of the climate system, as higher  Z500 on the east coast will amplify the increase in the number of\u0000events, especially the warm events. The relationship between the extreme\u0000weather index and high flows will be modified in the future as the snowpack\u0000reduces and rain becomes the main component of high-flow generation. This\u0000study shows the value of the CRCM5-LE dataset in simulating hydrometeorological extreme events in eastern Canada and better\u0000understanding the uncertainties associated with internal variability of climate.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"03 1","pages":"301-318"},"PeriodicalIF":0.0,"publicationDate":"2020-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86057781","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seasonal weather regimes in the North Atlantic region: towards new seasonality?","authors":"Florentin Breton, M. Vrac, P. Yiou, Pradeebane Vaittinada Ayar, Aglaé Jézéquel","doi":"10.5194/egusphere-egu2020-5449","DOIUrl":"https://doi.org/10.5194/egusphere-egu2020-5449","url":null,"abstract":"Abstract. European climate variability is shaped by atmospheric dynamics and local physical processes over the North Atlantic region. As both have strong seasonal features, a better insight of their future seasonality is essential to anticipate changes in weather conditions for human and natural systems. We explore the weather seasonality of the North Atlantic over 1979–2017 and 1979–2100 by using seasonal weather regimes (SWRs) defined by clustering year-round daily fields of geopotential height at 500 hPa (Z500) from the ERA-Interim reanalysis and 12 climate models of the Coupled Model Intercomparison Project fifth phase (CMIP5). The spatial and temporal variability of SWR structures is investigated, as well as associated patterns of surface air temperature. Although the climate models have biases, they reproduce structures and evolutions of SWRs similar to the reanalysis over 1979–2017: decreasing frequency of winter conditions (starting later and ending earlier in the year) and increasing frequency of summer conditions (starting earlier and ending later). These changes are stronger over 1979–2100 than over 1979–2017, associated with a large increase of North Atlantic seasonal mean Z500 and temperature. When using more SWRs (i.e. more freedom in the definition of seasonality), the changes over 1979–2100 correspond to a long-term swap between SWRs, resulting in similar structures (seasonal cycle and weather patterns) with respect to the evolution of the seasonal cycle of Z500 and temperature. To understand whether the evolution of the SWRs is linked to uniform Z500 increase (i.e. uniform warming), or to changes in Z500 spatial patterns (i.e. changes in circulation patterns), we remove the calendar trend in the Z500 regional average to define SWRs based on detrended data (d-SWRs). The temporal properties of d-SWRs appear almost constant, whereas their spatial patterns change. This indicates that the calendar Z500 regional trend drives the evolution of the SWRs and that the changing spatial patterns in d-SWRs account for the heterogeneity of this trend. Our study suggests that historical winter conditions will continue to decrease in the future while historical summer conditions continue to increase. It also suggests that according to an increasing seasonal cycle, the seasonality of weather conditions would not change in a major way.\u0000","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"1 1","pages":"1-28"},"PeriodicalIF":0.0,"publicationDate":"2020-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90869304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigating ENSO and its teleconnections under climate change in an ensemble view – a new perspective","authors":"T. Haszpra, M. Herein, T. Bódai","doi":"10.5194/esd-11-267-2020","DOIUrl":"https://doi.org/10.5194/esd-11-267-2020","url":null,"abstract":"Abstract. The changes in the El Nino–Southern Oscillation (ENSO) phenomenon and its precipitation-related teleconnections over the globe under climate change are investigated in the Community Earth System Model Large Ensemble from 1950 to 2100. For the investigation, a recently developed ensemble-based method, the snapshot empirical orthogonal function (SEOF) analysis, is used. The instantaneous ENSO pattern is defined as the leading mode of the SEOF analysis carried out at a given time instant over the ensemble. The corresponding principal components (PC1s) characterize the ENSO phases. By considering sea surface temperature (SST) regression maps, we find that the largest changes in the typical amplitude of SST fluctuations occur in the June–July–August–September (JJAS) season, in the Nino3–Nino3.4 (5 ∘  N–5 ∘  S, 170–90 ∘  W; NOAA Climate Prediction Center) region, and the western part of the Pacific Ocean; however, the increase is also considerable along the Equator in December–January–February (DJF). The Nino3 amplitude also shows an increase of about 20 % and 10 % in JJAS and DJF, respectively. The strength of the precipitation-related teleconnections of the ENSO is found to be nonstationary, as well. For example, the anticorrelation with precipitation in Australia in JJAS and the positive correlation in central and northern Africa in DJF are predicted to be more pronounced by the end of the 21th century. Half-year-lagged correlations, aiming to predict precipitation conditions from ENSO phases, are also studied. The Australian and Indonesian precipitation and that of the eastern part of Africa in both JJAS and DJF seem to be well predictable based on the ENSO phase, while the southern Indian precipitation relates to the half-year previous ENSO phase only in DJF. The strength of these connections increases, especially from the African region to the Arabian Peninsula.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"216 1","pages":"267-280"},"PeriodicalIF":0.0,"publicationDate":"2020-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81366812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impacts of land use change and elevated CO2 on the interannual variations and seasonal cycles of gross primary productivity in China","authors":"Binghao Jia, Binghao Jia, Xin Luo, Ximing Cai, Atul K. Jain, D. Huntzinger, Zhenghui Xie, N. Zeng, N. Zeng, J. Mao, Xiaoying Shi, A. Ito, Yaxing Wei, H. Tian, B. Poulter, D. Hayes, K. Schaefer","doi":"10.5194/ESD-11-235-2020","DOIUrl":"https://doi.org/10.5194/ESD-11-235-2020","url":null,"abstract":"Abstract. Climate change, rising CO2 concentration, and land\u0000use and land cover change (LULCC) are primary driving forces for terrestrial\u0000gross primary productivity (GPP), but their impacts on the temporal changes\u0000in GPP are uncertain. In this study, the effects of the three main factors\u0000on the interannual variation (IAV) and seasonal cycle amplitude (SCA) of GPP\u0000in China were investigated using 12 terrestrial biosphere models from the\u0000Multi-scale Synthesis and Terrestrial Model Intercomparison Project. The\u0000simulated ensemble mean value of China's GPP between 1981 and 2010, driven\u0000by common climate forcing, LULCC and CO2 data, was found to be\u0000 7.4±1.8  Pg C yr −1 . In general, climate was the dominant control\u0000factor of the annual trends, IAV and seasonality of China's GPP. The\u0000overall rising CO2 led to enhanced plant photosynthesis, thus\u0000increasing annual mean and IAV of China's total GPP, especially in\u0000northeastern and southern China, where vegetation is dense. LULCC decreased\u0000the IAV of China's total GPP by ∼7  %, whereas rising\u0000 CO2 induced an increase of 8 %. Compared to climate change and\u0000elevated CO2 , LULCC showed less contributions to GPP's temporal\u0000variation, and its impact acted locally, mainly in southwestern China.\u0000Furthermore, this study also examined subregional contributions to the\u0000temporal changes in China's total GPP. Southern and southeastern China\u0000showed higher contributions to China's annual GPP, whereas southwestern and\u0000central parts of China explained larger fractions of the IAV in China's GPP.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"67 1","pages":"235-249"},"PeriodicalIF":0.0,"publicationDate":"2020-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87031412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Biogeophysical impacts of forestation in Europe: first results from the LUCAS (Land Use and Climate Across Scales) regional climate model intercomparison","authors":"E. Davin, D. Rechid, M. Breil, R. Cardoso, E. Coppola, P. Hoffmann, L. Jach, E. Katragkou, N. de Noblet‐Ducoudré, K. Radtke, M. Raffa, P. Soares, Giannis Sofiadis, S. Strada, G. Strandberg, M. Tölle, K. Warrach‐Sagi, V. Wulfmeyer","doi":"10.5194/esd-11-183-2020","DOIUrl":"https://doi.org/10.5194/esd-11-183-2020","url":null,"abstract":"Abstract. The Land Use and Climate Across Scales Flagship Pilot\u0000Study (LUCAS FPS) is a coordinated community effort to improve the\u0000integration of land use change (LUC) in regional climate models (RCMs) and\u0000to quantify the biogeophysical effects of LUC on local to regional climate\u0000in Europe. In the first phase of LUCAS, nine RCMs are used to explore the\u0000biogeophysical impacts of re-/afforestation over Europe: two\u0000idealized experiments representing respectively a non-forested and a\u0000maximally forested Europe are compared in order to quantify spatial and\u0000temporal variations in the regional climate sensitivity to forestation. We\u0000find some robust features in the simulated response to forestation. In\u0000particular, all models indicate a year-round decrease in surface albedo,\u0000which is most pronounced in winter and spring at high latitudes. This\u0000results in a winter warming effect, with values ranging from +0.2 to +1 \u0000K on average over Scandinavia depending on models. However, there are also a\u0000number of strongly diverging responses. For instance, there is no agreement\u0000on the sign of temperature changes in summer with some RCMs predicting a\u0000widespread cooling from forestation (well below −2  K in most regions), a\u0000widespread warming (around +2  K or above in most regions) or a mixed\u0000response. A large part of the inter-model spread is attributed to the\u0000representation of land processes. In particular, differences in the\u0000partitioning of sensible and latent heat are identified as a key source of\u0000uncertainty in summer. Atmospheric processes, such as changes in incoming\u0000radiation due to cloud cover feedbacks, also influence the simulated\u0000response in most seasons. In conclusion, the multi-model approach we use\u0000here has the potential to deliver more robust and reliable information to\u0000stakeholders involved in land use planning, as compared to results based on\u0000single models. However, given the contradictory responses identified, our\u0000results also show that there are still fundamental uncertainties that need\u0000to be tackled to better anticipate the possible intended or unintended\u0000consequences of LUC on regional climates.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"69 1","pages":"183-200"},"PeriodicalIF":0.0,"publicationDate":"2020-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83825295","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Weather extremes over Europe under 1.5 °C and 2.0 °C global warming from HAPPI regional climate ensemble simulations","authors":"K. Sieck, C. Nam, L. Bouwer, D. Rechid, D. Jacob","doi":"10.5194/esd-2020-4","DOIUrl":"https://doi.org/10.5194/esd-2020-4","url":null,"abstract":"Abstract. This paper presents a novel data set of regional climate model simulations over Europe that significantly improves our ability to detect changes in weather extremes under low and moderate levels of global warming. The data set provides a unique and physically consistent data set, as it is derived from a large ensemble of regional climate model simulations. These simulations were driven by two global climate models from the international HAPPI consortium. The set consists of 100 × 10-year simulations and 25 × 10-year simulations, respectively. These large ensembles allow for regional climate change and weather extremes to be investigated with an improved signal-to-noise ratio compared to previous climate simulations. The changes in four climate indices for temperature targets of 1.5 °C and 2.0 °C global warming are quantified: number of days per year with daily mean near-surface apparent temperature of > 28 °C (ATG28); the yearly maximum 5-day sum of precipitation (RX5day); the daily precipitation intensity of the 50-yr return period (RI50yr); and the annual Consecutive Dry Days (CDD). This work shows that even for a small signal in projected global mean temperature, changes of extreme temperature and precipitation indices can be robustly estimated. For temperature related indices changes in percentiles can also be estimated with high confidence. Such data can form the basis for tailor-made climate information that can aid adaptive measures at a policy-relevant scales, indicating potential impacts at low levels of global warming at steps of 0.5 °C.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"57 1","pages":"1-17"},"PeriodicalIF":0.0,"publicationDate":"2020-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82954160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Emulating Earth system model temperatures with MESMER: from global mean temperature trajectories to grid-point-level realizations on land","authors":"L. Beusch, L. Gudmundsson, S. Seneviratne","doi":"10.5194/ESD-11-139-2020","DOIUrl":"https://doi.org/10.5194/ESD-11-139-2020","url":null,"abstract":"Abstract. Earth system models (ESMs) are invaluable tools to study the climate system's response to specific greenhouse gas emission pathways. Large single-model initial-condition and multi-model ensembles are used to investigate the range of possible responses and serve as input to climate impact and integrated assessment models. Thereby, climate signal uncertainty is propagated along the uncertainty chain and its effect on interactions between humans and the Earth system can be quantified. However, generating both single-model initial-condition and multi-model ensembles is computationally expensive. In this study, we assess the feasibility of geographically explicit climate model emulation, i.e., of statistically producing large ensembles of land temperature field time series that closely resemble ESM runs at a negligible computational cost. For this purpose, we develop a modular emulation framework which consists of (i) a global mean temperature module, (ii) a local temperature response module, and (iii) a local residual temperature variability module. Based on this framework, MESMER, a Modular Earth System Model Emulator with spatially Resolved output, is built. We first show that to successfully mimic single-model initial-condition ensembles of yearly temperature from 1870 to 2100 on grid-point to regional scales with MESMER, it is sufficient to train on a single ESM run, but separate emulators need to be calibrated for individual ESMs given fundamental inter-model differences. We then emulate 40 climate models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) to create a “superensemble”, i.e., a large ensemble which closely resembles a multi-model initial-condition ensemble. The thereby emerging ESM-specific emulator parameters provide essential insights on inter-model differences across a broad range of scales and characterize core properties of each ESM. Our results highlight that, for temperature at the spatiotemporal scales considered here, it is likely more advantageous to invest computational resources into generating multi-model ensembles rather than large single-model initial-condition ensembles. Such multi-model ensembles can be extended to superensembles with emulators like the one presented here.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"3 1","pages":"139-159"},"PeriodicalIF":0.0,"publicationDate":"2020-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79777025","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Amplified warming of seasonal cold extremes relative to the mean in the Northern Hemisphere extratropics","authors":"M. H. Gross, M. Donat, L. Alexander, S. Sherwood","doi":"10.5194/ESD-11-97-2020","DOIUrl":"https://doi.org/10.5194/ESD-11-97-2020","url":null,"abstract":"Abstract. Cold extremes are anticipated to warm at a faster rate than both hot extremes and average temperatures for much of the Northern Hemisphere.\u0000Anomalously warm cold extremes can affect numerous sectors, including human\u0000health, tourism and various ecosystems that are sensitive to cold temperatures. Using a selection of global climate models, this paper\u0000explores the accelerated warming of seasonal cold extremes relative to\u0000seasonal mean temperatures in the Northern Hemisphere extratropics. The\u0000potential driving physical mechanisms are investigated by assessing\u0000conditions on or prior to the day when the cold extreme occurs to understand how the different environmental fields are related. During winter, North America, Europe and much of Eurasia show amplified warming of cold extremes projected for the late 21st century, compared to the mid-20th century. This is shown to be largely driven by reductions in cold air temperature advection, suggested as a likely consequence of Arctic amplification. In spring and autumn, cold extremes are expected to warm faster than average temperatures for most of the Northern Hemisphere mid-latitudes to high latitudes, particularly Alaska, northern Canada and northern Eurasia. In the shoulder seasons, projected decreases in snow cover and associated reductions in surface albedo are suggested as the largest contributor affecting the accelerated rates of warming in cold extremes. The key findings of this study improve our understanding of the environmental conditions that contribute to the accelerated warming of cold extremes relative to mean temperatures.","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"44 1","pages":"97-111"},"PeriodicalIF":0.0,"publicationDate":"2020-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91543971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Climate engineering to mitigate the projected 21st-century terrestrial drying of the Americas: Carbon Capture vs. Sulfur Injection?","authors":"Yangyang Xu, Lei Lin, S. Tilmes, K. Dagon, L. Xia, C. Diao, W. Cheng, D. MacMartin, Zhili Wang, I. Simpson, Lorna Burnell","doi":"10.5194/esd-2020-2","DOIUrl":"https://doi.org/10.5194/esd-2020-2","url":null,"abstract":"Abstract. To mitigate the projected global warming in the 21st century, it is well recognized that society needs to cut CO2 emission and other short-lived warming agents aggressively. However, to stabilize the climate at a warming level closer to the present day, such as the well below 2 °C aspiration in the Paris agreement, a net-zero carbon emission by 2050 is still insufficient. The recent IPCC special report calls for a massive scheme to extract CO2 directly from the atmosphere, in addition to the decarbonization, to reach negative net emission at the mid-century mark. Another ambitious proposal is the solar radiation-based geoengineering schemes, including injecting sulfur gas into the stratosphere. Despite being in the public debate for years, these two leading geoengineering schemes have not been carefully examined under a consistent numerical modeling framework. Here we present a comprehensive analysis of climate impacts of these two geoengineering approaches using two recently available large-ensemble (> 10 members) model experiments conducted by a family of state-of-art Earth system models. The CO2-based mitigation simulation is designed to include both emissions cut and carbon capture. The solar radiation-based mitigation simulation is designed to inject the sulfur gas strategically at specified altitudes and latitudes and run a feedback control algorithm, to avoid common problems previously identified such as the over-cooling of the Tropics and large-scale precipitation shifts. Our analysis focuses on the projected aridity conditions over the Americas in the 21st century, in detailed terms of the mitigation potential, the temporal evolution, the spatial distribution (within North and South America), the relative efficiency, and the physical mechanisms. We show that sulfur injection, in contrast to previous notions of leading to excessive terrestrial drying (in terms of precipitation reduction) while offsetting the global mean greenhouse gas (GHG) warming, will instead mitigate the projected drying tendency under RCP8.5. The surface energy balance change induced by Sulfur injection, in addition to the well-known response in temperature and precipitation, plays a crucial role in determining the overall terrestrial hydroclimate response. However, when normalized by the same amount of avoided global warming, in these simulations, sulfur injection is less effective in limiting the worsening trend of regional land aridity in the Americas, when compared with carbon capture. Temporally, the climate benefit of Sulfur injection will emerge more quickly, even when both schemes are hypothetically started in the same year of 2020. Spatially, both schemes are effective in curbing the drying trend over North America. However, for South America, the Sulfur Injection scheme is particularly more effective for the sub-Amazon region (South Brazil), while the Carbon Capture scheme is more effective for the Amazon region. We conclude that despite the appar","PeriodicalId":11466,"journal":{"name":"Earth System Dynamics Discussions","volume":"24 1","pages":"1-39"},"PeriodicalIF":0.0,"publicationDate":"2020-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74275706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}