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1.
This study reports the first assessment of the compounding effects of land-use change and greenhouse gas warming effects on our understanding of projections of future climate. An AGCM simulation of the potential impacts of tropical deforestation and greenhouse warming on climate, employing a version of NCAR Community Climate Model (CCM1-Oz), is presented. The joint impacts of tropical deforestation and greenhouse warming are assessed by an experiment in which removal of tropical rainforests is imposed into a greenhouse-warmed climate. Results show that the joint climate changes over tropical rainforest regions comprise large reductions in surface evapotranspiration (by about –180 mm yr–1) andprecipitation (by about –312 mm yr–1) over the Amazon Basin, along with anincrease of surface temperature by +3.0 K. Over Southeast Asia, similar but weaker changes are found in this study. Precipitation is decreased by –172 mmyr–1, together with the surface warming of 2.1 K. Over tropical Africa, changes in regional climate is much weaker and with some different features, such as the increase of precipitation by 25 mm yr–1. Energy budgetanalyses demonstrates that the large increase of surface temperature in the joint experiment is not solely produced by the increase of CO2concentration, but is a joint effect of the reduction of surface evaporation (due to deforestation) and the increase of downward atmospheric longwave radiation (due to the doubling of CO2 concentration). Furthermore, impactsof tropical deforestation on the greenhouse-warmed climate are estimated by comparing a pair of tropical deforestation simulations. It is found that in CCM1-Oz, deforestation has very similar impacts on greenhouse-warmed regional climates as on current climates over tropical rainforest regions. The extra-tropical climatic response to tropical deforestation is identified in both sets of tropical deforestation experiments. Statistically significant responses are seen in the large-scale atmospheric circulation such as changes in the velocity potential and vertically integrated kinetic and potential energy fields. Wave propagation patterns are identified in the large-scale circulation anomalies, which provides a mechanism for interpreting the model responses in the extra-tropics. In addition, this study suggests that land-use change such as tropical deforestation may affect projections of future climate.  相似文献   

2.
土地利用和土地覆盖变化对气候系统影响的研究进展   总被引：8，自引：4，他引：4  
土地利用和土地覆盖变化（LUCC或LULCC）不仅对人类赖以生存的地球环境有重要影响,同时与人类福祉密切联系。人类活动对气候的强迫不仅包括温室气体排放导致的气候变暖,还通过直接改变地表物理性状以及间接改变其他生物地球物理过程和生物地球化学过程等对气候系统产生深刻影响。作者在此认识的基础上回顾了LUCC对气候系统影响的研究历史,结合新近的研究结果归纳了诸如森林砍伐、城市化、修坝等LUCC活动在区域和全球尺度的气候效应。LUCC具有高度的空间异质性,因此气候系统对它的反馈也具有明显的空间差异。由于全球平均后变化幅度相对区域上的小,LUCC对区域气候影响显著,而对全球气候影响不明显。它对区域气候的影响取决于反照率、蒸散发效率和地表粗糙率等变化的综合效应：在热带地区LUCC主要引起温度升高,在高纬度地区使温度下降。在全球尺度上LUCC导致气候的变暖主要通过减少蒸散发和潜热通量引起陆表水循环的改变,其次通过改变地表反照率导致辐射强迫改变。最后指出目前LUCC在气候变化学科中的研究所存在的问题。在此基础上提出了未来的研究首先需要评估的3个气候指标,并提倡多学科间的相互合作。  相似文献   

3.
In this study, a zonally-averaged statistical climate model (SDM) is used to investigate the impact of global warming on the distribution of the geobotanic zones over the globe. The model includes a parameterization of the biogeophysical feedback mechanism that links the state of surface to the atmosphere (a bidirectional interaction between vegetation and climate). In the control experiment (simulation of the present-day climate) the geobotanic state is well simulated by the model, so that the distribution of the geobotanic zones over the globe shows a very good agreement with the observed ones. The impact of global warming on the distribution of the geobotanic zones is investigated considering the increase of CO2 concentration for the B1, A2 and A1FI scenarios. The results showed that the geobotanic zones over the entire earth can be modified in future due to global warming. Expansion of subtropical desert and semi-desert zones in the Northern and Southern Hemispheres, retreat of glaciers and sea-ice, with the Arctic region being particularly affected and a reduction of the tropical rainforest and boreal forest can occur due to the increase of the greenhouse gases concentration. The effects were more pronounced in the A1FI and A2 scenarios compared with the B1 scenario. The SDM results confirm IPCC AR4 projections of future climate and are consistent with simulations of more complex GCMs, reinforcing the necessity of the mitigation of climate change associated to global warming.  相似文献   

4.
In accordance with numerous investigations, global climate warming due to the increased greenhouse gas content in the atmosphere can significantly influence the environment already in the near decades. In order to mitigate or prevent possible adverse consequences of this warming the technologies on reducing greenhouse gas emissions as well as a deliberate interference with climate, including its control, are under consideration. Let us analyze the present investigations on the estimate of the influence of a simultaneous increase in the atmospheric CO2 concentration and in the stratospheric aerosol on the global and regional climate, ozone layer, and World Ocean acidification. It is noted that the production and subsequent maintenance of the artificial aerosol layer in the stratosphere could, in principle, eliminate or retard climate warming, but it would be accompanied by a decrease in the global precipitation, especially in the tropical zone. Furthermore, the stratospheric aerosol screen does not solve the problem of the atmospheric CO2 increase, which in turn results in the further World Ocean acidification, and thus has an adverse effect on the marine part of the biosphere. Political and ethic issues connected with the deliberate global man interference with the natural environment are also under considerations.  相似文献   

5.
This study examines the potential impact of vegetation feedback on changes in summer climate aridity over the contiguous United States (US) due to the doubling of atmospheric CO2 concentration using a set of 100-year-long climate simulations made by a global climate model interactively coupled with a dynamic vegetation model. The Thornthwaite moisture index (I m ), which quantifies climate aridity on the basis of atmospheric water supply (i.e., precipitation) and atmospheric water demand (i.e., potential evapotranspiration, PET), is used to measure climate aridity. Warmer atmosphere and drier surface resulting from increased CO2 concentration increase climate aridity over most of the contiguous US. This phenomenon is due to larger increments in PET than in precipitation, regardless of the presence or absence of vegetation feedback. Compared to simulations without active dynamic vegetation feedback, the presence of vegetation feedback significantly alleviates the increase in aridity. This vegetation-feedback effect is most noticeable in the subhumid regions such as southern, midwestern and northwestern US, primarily by the increasing vegetation greenness. In these regions, the greening in response to warmer temperatures enhances moisture transfer from soil to atmosphere by evapotranspiration (ET). The increased ET and subsequent moistening over land areas result in weaker surface warming (1–2?K) and PET (3–10?mm?month?1), and greater precipitation (4–10?mm?month?1). Collectively, they result in moderate increases in I m . Our results suggest that moistening by enhanced vegetation feedback may prevent aridification under climatic warming especially in areas vulnerable to climate change, with consequent implications for mitigation strategies.  相似文献   

6.
Large-scale conversion of tropical forests into pastures or annual crops will likely lead to changes in the local microclimate of those regions. Larger diurnal fluctuations of surface temperature and humidity deficit, increased surface runoff during rainy periods and decreased runoff during the dry season, and decreased soil moistrue are to be expected.It is likely that evapotranspiration will be reduced because of less available radiative energy at the canopy level since grass presents a higher albedo than forests, also because of the reduced availability of soil moisture at the rooting zone primarily during the dry season. Recent results from general circulation model (GCM) simulations of Amazonian deforestation seem to suggest that the equilibrium climate for a grassy vegetation in Amazonia would be one in which regional precipitation would be significantly reduced.Global climate changes probably will occur if there is a marked change in rainfall patterns in tropical forest regions as a result of deforestation. Besides that, biomass burning of tropical forests is likely adding CO2 into the atmosphere, thus contributing to the enhanced greenhouse warming.  相似文献   

7.
In this the second of a two-part study, we examine the physical mechanisms responsible for the increasing contrast of the land–sea surface air temperature (SAT) in summertime over the Far East, as observed in recent decades and revealed in future climate projections obtained from a series of transient warming and sensitivity experiments conducted under the umbrella of the Coupled Model Intercomparison Project phase 5. On a global perspective, a strengthening of land–sea SAT contrast in the transient warming simulations of coupled atmosphere–ocean general circulation models is attributed to an increase in sea surface temperature (SST). However, in boreal summer, the strengthened contrast over the Far East is reproduced only by increasing atmospheric CO2 concentration. In response to SST increase alone, the tropospheric warming over the interior of the mid- to high-latitude continents including Eurasia are weaker than those over the surrounding oceans, leading to a weakening of the land–sea SAT contrast over the Far East. Thus, the increasing contrast and associated change in atmospheric circulation over East Asia is explained by CO2-induced continental warming. The degree of strengthening of the land–sea SAT contrast varies in different transient warming scenarios, but is reproduced through a combination of the CO2-induced positive and SST-induced negative contributions to the land–sea contrast. These results imply that changes of climate patterns over the land–ocean boundary regions are sensitive to future scenarios of CO2 concentration pathways including extreme cases.  相似文献   

8.
Vegetation is a major component of the climate system because of its controls on the energy and water balance over land. This functioning changes because of the physiological response of leaves to increased CO2. A climate model is used to compare these changes with the climate changes from radiative forcing by greenhouse gases. For this purpose, we use the Community Earth System Model coupled to a slab ocean. Ensemble integrations are done for current and doubled CO2. The consequent reduction of transpiration and net increase of surface radiative heating from reduction in cloudiness increases the temperature over land by a significant fraction of that directly from the radiative warming by CO2. Large-scale atmospheric circulation adjustments result. In particular, over the tropics, a low-level westerly wind anomaly develops associated with reduced geopotential height over land, enhancing moisture transport and convergence, and precipitation increases over the western Amazon, the Congo basin, South Africa, and Indonesia, while over mid-latitudes, land precipitation decreases from reduced evapotranspiration. On average, land precipitation is enhanced by 0.03 mm day?1 (about 19 % of the CO2 radiative forcing induced increase). This increase of land precipitation with decreased ET is an apparent negative feedback, i.e., less ET makes more precipitation. Global precipitation is slightly reduced. Runoff increases associated with both the increased land precipitation and reduced evapotranspiration. Examining the consistency of the variations among ensemble members shows that vegetation feedbacks on precipitation are more robust over the tropics and in mid to high latitudes than over the subtropics where vegetation is sparse and the internal climate variability has a larger influence.  相似文献   

9.
Summary A coupled biosphere-atmosphere statistical-dynamical model (SDM) is used to study the climatic effects of Amazonian deforestation. A soil moisture model based on BATS has been incorporated into the SDM in order to study the biogeophysical feedback of change in surface characteristics to regional climate due to the deforestation. In the control experiment, the mean annual and mean seasonal climate is well simulated by the model when compared with NCEP/NCAR reanalysis data. In the deforestation experiment, the evergreen broadleaf trees in the Amazonian region are substituted by short grass. The effects of Amazonian deforestation on regional climate are analysed taking into account the model simulations for the land portion of the latitude belts comprising the tropical region. Amazonian deforestation results in regional climate changes such as a decrease in evaporation, precipitation, available surface net radiation and soil moisture content, and an increase in temperatures and sensible heat flux. The reduction in transpiration was responsible for the most part of the decrease in total evapotranspiration. The reduction in precipitation was larger than the decrease in evapotranspiration so that runoff was reduced. The simulation of the diurnal cycle of the surface temperature shows an increase in temperature during the day and a decrease at night, which is in agreement with observations, whereas earlier GCM experiments showed an increase both during the day and night. In general, the changes in temperature and energy fluxes are in good agreement with GCM experiments, showing that the SDM is able to simulate the characteristics of the tropical climate that are associated with the substitution of forest by pasture areas.  相似文献   

10.
The concentration of carbon dioxide in the atmosphere acts to control the stomatal conductance of plants. There is observational and modelling evidence that an increase in the atmospheric concentration of CO2 would suppress the evapotranspiration (ET) rate over land. This process is known as CO2 physiological forcing and has been shown to induce changes in surface temperature and continental runoff. We analyse two transient climate simulations for the twenty-first century to isolate the climate response to the CO2 physiological forcing. The land surface warming associated with the decreased ET rate is accompanied by an increase in the atmospheric lapse rate, an increase in specific humidity, but a decrease in relative humidity and stratiform cloud over land. We find that the water vapour feedback more than compensates for the decrease in latent heat flux over land as far as the budget of atmospheric water vapour is concerned. There is evidence that surface snow, water vapour and cloudiness respond to the CO2 physiological forcing and all contribute to further warm the climate system. The climate response to the CO2 physiological forcing has a quite different signature to that from the CO2 radiative forcing, especially in terms of the changes in the temperature vertical profile and surface energy budget over land.  相似文献   

11.
Wilhelm May 《Climate Dynamics》2008,31(2-3):283-313
In this study, concentrations of the well-mixed greenhouse gases as well as the anthropogenic sulphate aerosol load and stratospheric ozone concentrations are prescribed to the ECHAM5/MPI-OM coupled climate model so that the simulated global warming does not exceed 2°C relative to pre-industrial times. The climatic changes associated with this so-called “2°C-stabilization” scenario are assessed in further detail, considering a variety of meteorological and oceanic variables. The climatic changes associated with such a relatively weak climate forcing supplement the recently published fourth assessment report by the IPCC in that such a stabilization scenario can only be achieved by mitigation initiatives. Also, the impact of the anthropogenic sulphate aerosol load and stratospheric ozone concentrations on the simulated climatic changes is investigated. For this particular climate model, the 2°C-stabilization scenario is characterized by the following atmospheric concentrations of the well-mixed greenhouse gases: 418 ppm (CO2), 2,026 ppb (CH4), and 331 ppb (N2O), 786 ppt (CFC-11) and 486 ppt (CFC-12), respectively. These greenhouse gas concentrations correspond to those for 2020 according to the SRES A1B scenario. At the same time, the anthropogenic sulphate aerosol load and stratospheric ozone concentrations are changed to the level in 2100 (again, according to the SRES A1B scenario), with a global anthropogenic sulphur dioxide emission of 28 TgS/year leading to a global anthropogenic sulphate aerosol load of 0.23 TgS. The future changes in climate associated with the 2°C-stabilization scenario show many of the typical features of other climate change scenarios, including those associated with stronger climatic forcings. That are a pronounced warming, particularly at high latitudes accompanied by a marked reduction of the sea-ice cover, a substantial increase in precipitation in the tropics as well as at mid- and high latitudes in both hemispheres but a marked reduction in the subtropics, a significant strengthening of the meridional temperature gradient between the tropical upper troposphere and the lower stratosphere in the extratropics accompanied by a pronounced intensification of the westerly winds in the lower stratosphere, and a strengthening of the westerly winds in the Southern Hemisphere extratropics throughout the troposphere. The magnitudes of these changes, however, are somewhat weaker than for the scenarios associated with stronger global warming due to stronger climatic forcings, such as the SRES A1B scenario. Some of the climatic changes associated with the 2°C-stabilization are relatively strong with respect to the magnitude of the simulated global warming, i.e., the pronounced warming and sea-ice reduction in the Arctic region, the strengthening of the meridional temperature gradient at the northern high latitudes and the general increase in precipitation. Other climatic changes, i.e., the El Niño like warming pattern in the tropical Pacific Ocean and the corresponding changes in the distribution of precipitation in the tropics and in the Southern Oscillation, are not as markedly pronounced as for the scenarios with a stronger global warming. A higher anthropogenic sulphate aerosol load (for 2030 as compared to the level in 2100 according to the SRES A1B scenario) generally weakens the future changes in climate, particularly for precipitation. The most pronounced effects occur in the Northern Hemisphere and in the tropics, where also the main sources of anthropogenic sulphate aerosols are located.  相似文献   

12.
The change in the teleconnections of both El Niño and La Niña over the North Pacific and American regions due to a future greenhouse warming has been analyzed herein by means of diagnostics of the Intergovernmental Panel on Climate Change-Fourth Assessment Report (IPCC-AR4) coupled general circulation models (CGCMs). Among the IPCC-AR4 CGCM simulations, the composites of the eight-member multimodel ensemble are analyzed. In most CGCMs, the tropical Pacific warming due to the increase of CO2 concentration in the atmosphere promotes the main convection centers in the equatorial Pacific associated with both El Niño and La Niña to the east. The eastward shift of the convection center causes a systematic eastward shift of not only El Niño but also La Niña teleconnection patterns over the North Pacific and America, which is demonstrated in the composite maps of 500 hPa circulation, surface temperature, and the precipitation against El Niño and La Niña, as observed in a comparison between the pre-industrial and CO2 doubling experiments. Thus, a systematic eastward migration of convection centers in the tropical Pacific associated with both El Niño and La Niña due to a future global warming commonly causes the eastward shift of the atmospheric teleconnection patterns over the Northern Hemisphere.  相似文献   

13.
Recent land cover changes on the Tibetan Plateau: a review   总被引：6，自引：0，他引：6  
This paper reviews the land cover changes on the Tibetan Plateau during the last 50 years partly caused by natural climate change and, more importantly, influenced by human activities. Recent warming trends on the plateau directly influence the permafrost and snow melting and will impact on the local ecosystem greatly. Human activities increased rapidly on the plateau during the last half century and have significant impacts on land use. Significant land cover changes on the Tibetan Plateau include permafrost and grassland degradation, urbanization, deforestation and desertification. These changes not only impact on local climate and environment, but also have important hydrological implications for the rivers which originate from the plateau. The most noticeable disasters include the flooding at the upper reaches of Yangtze River and droughts along the middle and lower reaches of Yellow River. Future possible land cover changes under future global climate warming are important but hard to assess due to the deficits of global climate model in this topographically complex area. Integrated investigation of climate and ecosystems, including human-beings, are highly recommended for future studies.  相似文献   

14.
In this study, a coupled atmosphere-surface “climate feedback-response analysis method” (CFRAM) was applied to the slab ocean model version of the NCAR CCSM3.0 to understand the tropospheric warming due to a doubling of CO2 concentration through quantifying the contributions of each climate feedback process. It is shown that the tropospheric warming displays distinct meridional and vertical patterns that are in a good agreement with the multi-model mean projection from the IPCC AR4. In the tropics, the warming in the upper troposphere is stronger than in the lower troposphere, leading to a decrease in temperature lapse rate, whereas in high latitudes the opposite it true. In terms of meridional contrast, the lower tropospheric warming in the tropics is weaker than that in high latitudes, resulting in a weakened meridional temperature gradient. In the upper troposphere the meridional temperature gradient is enhanced due to much stronger warming in the tropics than in high latitudes. Using the CFRAM method, we analyzed both radiative feedbacks, which have been emphasized in previous climate feedback analysis, and non-radiative feedbacks. It is shown that non-radiative (radiative) feedbacks are the major contributors to the temperature lapse rate decrease (increase) in the tropical (polar) region. Atmospheric convection is the leading contributor to temperature lapse rate decrease in the tropics. The cloud feedback also has non-negligible contributions. In the polar region, water vapor feedback is the main contributor to the temperature lapse rate increase, followed by albedo feedback and CO2 forcing. The decrease of meridional temperature gradient in the lower troposphere is mainly due to strong cooling from convection and cloud feedback in the tropics and the strong warming from albedo feedback in the polar region. The strengthening of meridional temperature gradient in the upper troposphere can be attributed to the warming associated with convection and cloud feedback in the tropics. Since convection is the leading contributor to the warming differences between tropical lower and upper troposphere, and between the tropical and polar regions, this study indicates that tropical convection plays a critical role in determining the climate sensitivity. In addition, the CFRAM analysis shows that convective process and water vapor feedback are the two major contributors to the tropical upper troposphere temperature change, indicating that the excessive upper tropospheric warming in the IPCC AR4 models may be due to overestimated warming from convective process or underestimated cooling due to water vapor feedback.  相似文献   

15.
An increase in atmospheric carbon dioxide concentration has both a radiative (greenhouse) effect and a physiological effect on climate. The physiological effect forces climate as plant stomata do not open as wide under enhanced CO2 levels and this alters the surface energy balance by reducing the evapotranspiration flux to the atmosphere, a process referred to as ‘carbon dioxide physiological forcing’. Here the climate impact of the carbon dioxide physiological forcing is isolated using an ensemble of twelve 5-year experiments with the Met Office Hadley Centre HadCM3LC fully coupled atmosphere–ocean model where atmospheric carbon dioxide levels are instantaneously quadrupled and thereafter held constant. Fast responses (within a few months) to carbon dioxide physiological forcing are analyzed at a global and regional scale. Results show a strong influence of the physiological forcing on the land surface energy budget, hydrological cycle and near surface climate. For example, global precipitation rate reduces by ~3% with significant decreases over most land-regions, mainly from reductions to convective rainfall. This fast hydrological response is still evident after 5 years of model integration. Decreased evapotranspiration over land also leads to land surface warming and a drying of near surface air, both of which lead to significant reductions in near surface relative humidity (~6%) and cloud fraction (~3%). Patterns of fast responses consistently show that results are largest in the Amazon and central African forest, and to a lesser extent in the boreal and temperate forest. Carbon dioxide physiological forcing could be a source of uncertainty in many model predicted quantities, such as climate sensitivity, transient climate response and the hydrological sensitivity. These results highlight the importance of including biological components of the Earth system in climate change studies.  相似文献   

16.
 A set of sensitivity experiments with the climate system model of intermediate complexity CLIMBER-2 was performed to compare its sensitivity to changes in different types of forcings and boundary conditions with the results of comprehensive models (GCMs). We investigated the climate system response to changes in freshwater flux into the Northern Atlantic, CO2 concentration, solar insolation, and vegetation cover in the boreal zone and in the tropics. All these experiments were compared with the results of corresponding experiments performed with different GCMs. Qualitative, and in many respects, quantitative agreement between the results of CLIMBER-2 and GCMs demonstrate the ability of our climate system model of intermediate complexity to address diverse aspects of the climate change problem. In addition, we used our model for a series of experiments to assess the impact of some climate feedbacks and uncertainties in model parameters on the model sensitivity to different forcings. We studied the role of freshwater feedback and vertical ocean diffusivity for the stability properties of the thermohaline ocean circulation. We show that freshwater feedback plays a minor role, while changes of vertical diffusivity in the ocean considerably affect the circulation stability. In global warming experiments we analysed the impact of hydrological sensitivity and vertical diffusivity on the long-term evolution of the thermohaline circulation. In the boreal and tropical deforestation experiments we assessed the role of an interactive ocean and showed that for both types of deforestation scenarios, an interactive ocean leads to an additional cooling due to albedo and water vapour feedbacks. Received: 28 May 2000 / Accepted: 9 November 2000  相似文献   

17.
Two coupled general circulation models, i.e., the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) models, were chosen to examine changes in mixed layer depth (MLD) in the equatorial tropical Pacific and its relationship with ENSO under climate change projections. The control experiment used pre-industrial greenhouse gas concentrations whereas the 2 × CO2 experiment used doubled CO2 levels. In the control experiment, the MLD simulated in the MRI model was shallower than that in the GFDL model. This resulted in the tropical Pacific’s mean sea surface temperature (SST) increasing at different rates under global warming in the two models. The deeper the mean MLD simulated in the control simulation, the lesser the warming rate of the mean SST simulated in the 2 × CO2 experiment. This demonstrates that the MLD is a key parameter for regulating the response of tropical mean SST to global warming. In particular, in the MRI model, increased stratification associated with global warming amplified wind-driven advection within the mixed layer, leading to greater ENSO variability. On the other hand, in the GFDL model, wind-driven currents were weak, which resulted in mixed-layer dynamics being less sensitive to global warming. The relationship between MLD and ENSO was also examined. Results indicated that the non-linearity between the MLD and ENSO is enhanced from the control run to the 2 × CO2 run in the MRI model, in contrast, the linear relationship between the MLD index and ENSO is unchanged despite an increase in CO2 concentrations in the GFDL model.  相似文献   

18.
Increasing concentrations of atmospheric CO2 and other greenhouse gases are expected to contribute to a global warming. This paper examines the potential implications of a climatic change corresponding to a doubling of atmospheric concentrations of CO2 on crop production opportunities throughout Ontario, a major food producing region in Canada. The climate is projected to become warmer and drier, but the extent of these shifts are expected to vary from region to region within Ontario. The effect of this altered climate on crop yields and the area of land capable of supporting specific crops varies according to region, soil quality and crop type. Most notable are the enhanced opportunities for grains and oilseeds in the northern regions, and the diminished production prospects for most crops in the most southerly parts of Ontario.  相似文献   

19.
A recent modelling study has shown that precipitation and runoff over land would increase when the reflectivity of marine clouds is increased to counter global warming. This implies that large scale albedo enhancement over land could lead to a decrease in runoff over land. In this study, we perform simulations using NCAR CAM3.1 that have implications for Solar Radiation Management geoengineering schemes that increase the albedo over land. We find that an increase in reflectivity over land that mitigates the global mean warming from a doubling of CO2 leads to a large residual warming in the southern hemisphere and cooling in the northern hemisphere since most of the land is located in northern hemisphere. Precipitation and runoff over land decrease by 13.4 and 22.3%, respectively, because of a large residual sinking motion over land triggered by albedo enhancement over land. Soil water content also declines when albedo over land is enhanced. The simulated magnitude of hydrological changes over land are much larger when compared to changes over oceans in the recent marine cloud albedo enhancement study since the radiative forcing over land needed (?8.2?W?m?2) to counter global mean radiative forcing from a doubling of CO2 (3.3?W?m?2) is approximately twice the forcing needed over the oceans (?4.2?W?m?2). Our results imply that albedo enhancement over oceans produce climates closer to the unperturbed climate state than do albedo changes on land when the consequences on land hydrology are considered. Our study also has important implications for any intentional or unintentional large scale changes in land surface albedo such as deforestation/afforestation/reforestation, air pollution, and desert and urban albedo modification.  相似文献   

20.
Climate sensitivity is an important index that measures the relationship between the increase in greenhouse gases and the magnitude of global warming. Uncertainties in climate change projection and climate modeling are mostly related to the climate sensitivity. The climate sensitivities of coupled climate models determine the magnitudes of the projected global warming. In this paper, the authors thoroughly review the literature on climate sensitivity, and discuss issues related to climate feedback processes and the methods used in estimating the equilibrium climate sensitivity and transient climate response (TCR), including the TCR to cumulative CO2 emissions. After presenting a summary of the sources that affect the uncertainty of climate sensitivity, the impact of climate sensitivity on climate change projection is discussed by addressing the uncertainties in 2°C warming. Challenges that call for further investigation in the research community, in particular the Chinese community, are discussed.  相似文献   

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