Constraints on radiative forcing and future climate change from observations and climate model ensembles

The assessment of uncertainties in global warming projections is often based on expert judgement, because a number of key variables in climate change are poorly quantified. In particular, the sensitivity of climate to changing greenhouse-gas concentrations in the atmosphere and the radiative forcing effects by aerosols are not well constrained, leading to large uncertainties in global warming simulations. Here we present a Monte Carlo approach to produce probabilistic climate projections, using a climate model of reduced complexity. The uncertainties in the input parameters and in the model itself are taken into account, and past observations of oceanic and atmospheric warming are used to constrain the range of realistic model responses. We obtain a probability density function for the present-day total radiative forcing, giving 1.4 to 2.4 W m-2 for the 5-95 per cent confidence range, narrowing the global-mean indirect aerosol effect to the range of 0 to -1.2 W m-2. Ensemble simulations for two illustrative emission scenarios suggest a 40 per cent probability that global-mean surface temperature increase will exceed the range predicted by the Intergovernmental Panel on Climate Change (IPCC), but only a 5 per cent probability that warming will fall below that range.     

Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model

The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon-climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr(-1) is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.     

Simulation of historical and projected climate change in arid and semiarid areas by CMIP5 models

Based on Climatic Research Unit Time Series3.1 temperature and Global Precipitation Climatology Center full data reanalysis version 6 precipitation data,the abilities of climate models from the fifth phase of the Coupled Model Intercomparison Project to simulate climate changes over arid and semiarid areas were assessed.Simulations of future climate changes under different representative concentration pathways(RCPs)were also examined.The key findings were that most of the models are able to capture the dominant features of the spatiotemporal changes in temperature,especially the geographic distribution,during the past 60 years,both globally as well as over arid and semiarid areas.In addition,the models can reproduce the observed warming trends,but with magnitudes generally less than the observations of around0.1–0.3°C/50a.Compared to temperature,the models perform worse in simulating the annual evolution of observed precipitation,underestimating both the variability and tendency,and there is a huge spread among the models in terms of their simulated precipitation results.The multimodel ensemble mean is overall superior to any individual model in reproducing the observed climate changes.In terms of future climate change,an ongoing warming projected by the multi-model ensemble over arid and semiarid areas can clearly be seen under different RCPs,especially under the high emissions scenario(RCP8.5),which is twice that of the moderate scenario(RCP4.5).Unlike the increasing temperature,precipitation changes vary across areas and are more significant under high-emission RCPs,with more precipitation over wet areas but less precipitation over dry areas.In particular,northern China is projected to be one of the typical areas experiencing significantly increased temperature and precipitation in the future.     

Climate sensitivity constrained by CO2 concentrations over the past 420 million years

A firm understanding of the relationship between atmospheric carbon dioxide concentration and temperature is critical for interpreting past climate change and for predicting future climate change. A recent synthesis suggests that the increase in global-mean surface temperature in response to a doubling of the atmospheric carbon dioxide concentration, termed 'climate sensitivity', is between 1.5 and 6.2 degrees C (5-95 per cent likelihood range), but some evidence is inconsistent with this range. Moreover, most estimates of climate sensitivity are based on records of climate change over the past few decades to thousands of years, when carbon dioxide concentrations and global temperatures were similar to or lower than today, so such calculations tend to underestimate the magnitude of large climate-change events and may not be applicable to climate change under warmer conditions in the future. Here we estimate long-term equilibrium climate sensitivity by modelling carbon dioxide concentrations over the past 420 million years and comparing our calculations with a proxy record. Our estimates are broadly consistent with estimates based on short-term climate records, and indicate that a weak radiative forcing by carbon dioxide is highly unlikely on multi-million-year timescales. We conclude that a climate sensitivity greater than 1.5 degrees C has probably been a robust feature of the Earth's climate system over the past 420 million years, regardless of temporal scaling.     

东亚地区典型极端气候指标未来预估及高温下人口暴露度研究

基于地球系统模式、CMIP6 (第六次全球耦合模式比较计划)温室气体排放和大气成分数据以及人口数据, 研究区域均温变化与极端气候指标变化之间的相关关系, 进而探讨9种SSPs (共享社会经济路径)-RCPs(典型浓度路径)情景下东亚3种极端气候指标的未来预估和区域高温下人口暴露度的变化及归因。结果表明: ) 全球地表均温变化和区域极端气候指标具有稳健的相关关系, 可以用于区域极端气候指标的未来预估; 2) 与基准期1861—1880年相比, 未来数十年间东亚地区在5种情景(SSP2-4.5, SSP4-6.0, SSP3-LowNTCF, SSP3-7.0-Baseline和SSP5-8.5-Baseline)下面临持续增加的极端气候风险, 而空气污染物减排与控制措施可以显著地降低该风险, 不过, 气候对温室气体及气溶胶排放控制措施的响应具有一定的时间滞后效应, 为预防可能面临的极端气候事件风险, 减排及控制措施应提前布局和实施; 3) 东亚典型区域未来高温下的人口暴露度受气候因子和人口因子共同作用, 随时间动态变化且具有明显的区域差异, 多数情景下, 气候因子对区域高温下人口暴露度的影响逐渐减弱, 而人口因子的影响逐渐加强, 华南地区高温下的人口暴露度明显高于西南和华中地区, 其中气候因子的相对贡献比例也高于后两个地区。     

A large discontinuity in the mid-twentieth century in observed global-mean surface temperature

Data sets used to monitor the Earth's climate indicate that the surface of the Earth warmed from approximately 1910 to 1940, cooled slightly from approximately 1940 to 1970, and then warmed markedly from approximately 1970 onward. The weak cooling apparent in the middle part of the century has been interpreted in the context of a variety of physical factors, such as atmosphere-ocean interactions and anthropogenic emissions of sulphate aerosols. Here we call attention to a previously overlooked discontinuity in the record at 1945, which is a prominent feature of the cooling trend in the mid-twentieth century. The discontinuity is evident in published versions of the global-mean temperature time series, but stands out more clearly after the data are filtered for the effects of internal climate variability. We argue that the abrupt temperature drop of approximately 0.3 degrees C in 1945 is the apparent result of uncorrected instrumental biases in the sea surface temperature record. Corrections for the discontinuity are expected to alter the character of mid-twentieth century temperature variability but not estimates of the century-long trend in global-mean temperatures.     

Uncertainty in predictions of the climate response to rising levels of greenhouse gases

The range of possibilities for future climate evolution needs to be taken into account when planning climate change mitigation and adaptation strategies. This requires ensembles of multi-decadal simulations to assess both chaotic climate variability and model response uncertainty. Statistical estimates of model response uncertainty, based on observations of recent climate change, admit climate sensitivities--defined as the equilibrium response of global mean temperature to doubling levels of atmospheric carbon dioxide--substantially greater than 5 K. But such strong responses are not used in ranges for future climate change because they have not been seen in general circulation models. Here we present results from the 'climateprediction.net' experiment, the first multi-thousand-member grand ensemble of simulations using a general circulation model and thereby explicitly resolving regional details. We find model versions as realistic as other state-of-the-art climate models but with climate sensitivities ranging from less than 2 K to more than 11 K. Models with such extreme sensitivities are critical for the study of the full range of possible responses of the climate system to rising greenhouse gas levels, and for assessing the risks associated with specific targets for stabilizing these levels.     

气候变化对中国农业的影响

 在全球气候变化背景下,中国的气温不断增高,近50年中国年平均地表气温增加了1.1℃,明显高于全球;降水变化趋势不明显,年代际波动较大,也存在明显的地区差别;极端天气气候事件不断增多。未来气候变化情景,预计中国北方增温幅度高于南方,青藏高原增温最明显,年降水量增加显著区域为华北、西北及东北地区,长江中下游沿岸及其以南地区有小幅度增加。气候变暖将使粮食作物水稻、玉米和小麦的生育期缩短,产量下降;有利于棉花生产,能提高北方棉花产量和品质;三熟区面积将扩大约22.4%,一熟区面积约缩小23.1%,作物种植结构和作物品种的布局将发生变化;主要农作物病虫害呈加重趋势;对温带和寒带的家畜生长是有利的,对热带和亚热带家畜和牧草生长不利;中国四大海区主要经济鱼种的产量和渔获量有不同程度的降低;气候变暖将使中国各类自然植被发生明显北移,土地荒漠化危害范围加大,土壤肥力下降,并增加农业灌溉的需水量,农业水资源供需矛盾加剧。中国农业应对气候变化包括减缓和适应两个方面,应减缓和适应并重。     

CMIP6多模式在青藏高原的适应性评估及未来气候变化预估

随着CMIP6（coupled model intercomparison project phase 6）计划进行,新一代大气环流模式（general circulation model, GCM）输出结果陆续发布,及时探究在新模式新情景下青藏高原未来降水及气温的变化规律至关重要．在对CMIP6多模式进行适应性评估的基础上,运用DM（direct method）统计降尺度方法,以1979—2014年为基准期,预估青藏高原未来近期（2031—2050年）、远期（2061—2080年）在共享社会经济路径与典型浓度路径组合情景（shared socioeconomic pathways and the representative concentration pathways, SSP)包括低强迫情景(SSP126)、中等强迫情景（SSP245）、中等至高强迫情景（SSP370）、高强迫情景（SSP585）下的降水、平均气温、最低气温、最高气温的时空演变规律．结果表明:相较于基准期,不同GCM对青藏高原未来降水的预估总体呈现增加趋势,近期降水较基准期变幅为?3%~16%,远期变幅为?1%~21%．未来平均气温、最低气温和最高气温均呈现一致的增温趋势,且增幅较为一致．相较于基准期,近期气温变化范围为0.9~2.3 ℃,远期气温变化范围为1.01~4.6 ℃．随着排放强度的增加,三者升温趋势愈加显著,即升温趋势由强至弱排序为SSP585、SSP370、SSP245、SSP126．此外,青藏高原气温变化在海拔高度上具有显著的依赖性,整体表现为青藏高原北部高海拔地区增温高于青藏高原东南部低海拔地区．研究结果可为揭示气候变化对高寒区水循环的影响机制提供科学依据．      

Low sea level rise projections from mountain glaciers and icecaps under global warming

The mean sea level has been projected to rise in the 21st century as a result of global warming. Such projections of sea level change depend on estimated future greenhouse emissions and on differing models, but model-average results from a mid-range scenario (A1B) suggests a 0.387-m rise by 2100 (refs 1, 2). The largest contributions to sea level rise are estimated to come from thermal expansion (0.288 m) and the melting of mountain glaciers and icecaps (0.106 m), with smaller inputs from Greenland (0.024 m) and Antarctica (- 0.074 m). Here we apply a melt model and a geometric volume model to our lower estimate of ice volume and assess the contribution of glaciers to sea level rise, excluding those in Greenland and Antarctica. We provide the first separate assessment of melt contributions from mountain glaciers and icecaps, as well as an improved treatment of volume shrinkage. We find that icecaps melt more slowly than mountain glaciers, whose area declines rapidly in the 21st century, making glaciers a limiting source for ice melt. Using two climate models, we project sea level rise due to melting of mountain glaciers and icecaps to be 0.046 and 0.051 m by 2100, about half that of previous projections.     

洮儿河流域平原区气候变化情景下浅层地下水水位动态响应分析

利用研究区降水、气温、地表水径流和地下水埋深数据,使用Mann-Kendall非参数检验法,分析水文气象要素变化趋势,结合研究区水文地质概况,建立地下水数值模型,对未来气候变化下的地下水水位动态进行预测．结果表明:研究区地下水埋深呈显著增加趋势,降水量增加不显著,气温呈升高趋势,地表径流显著减少;通过建立的Visual MODFLOW模型,对基准情景（基准期平均降水量条件）和3种气候情景（SSP126、SSP245、SSP585）下研究区未来地下水位进行预测:基准情景和3种气候情景下研究区北部浅层地下水埋深持续增加,南部地下水埋深有所减少;3种气候情景下地下水埋深均大于基准情景下地下水位埋深．      

Quantifying the uncertainty in forecasts of anthropogenic climate change

Forecasts of climate change are inevitably uncertain. It is therefore essential to quantify the risk of significant departures from the predicted response to a given emission scenario. Previous analyses of this risk have been based either on expert opinion, perturbation analysis of simplified climate models or the comparison of predictions from general circulation models. Recent observed changes that appear to be attributable to human influence provide a powerful constraint on the uncertainties in multi-decadal forecasts. Here we assess the range of warming rates over the coming 50 years that are consistent with the observed near-surface temperature record as well as with the overall patterns of response predicted by several general circulation models. We expect global mean temperatures in the decade 2036-46 to be 1-2.5 K warmer than in pre-industrial times under a 'business as usual' emission scenario. This range is relatively robust to errors in the models' climate sensitivity, rate of oceanic heat uptake or global response to sulphate aerosols as long as these errors are persistent over time. Substantial changes in the current balance of greenhouse warming and sulphate aerosol cooling would, however, increase the uncertainty. Unlike 50-year warming rates, the final equilibrium warming after the atmospheric composition stabilizes remains very uncertain, despite the evidence provided by the emerging signal.     

Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability

Systematic climate shifts have been linked to multidecadal variability in observed sea surface temperatures in the North Atlantic Ocean. These links are extensive, influencing a range of climate processes such as hurricane activity and African Sahel and Amazonian droughts. The variability is distinct from historical global-mean temperature changes and is commonly attributed to natural ocean oscillations. A number of studies have provided evidence that aerosols can influence long-term changes in sea surface temperatures, but climate models have so far failed to reproduce these interactions and the role of aerosols in decadal variability remains unclear. Here we use a state-of-the-art Earth system climate model to show that aerosol emissions and periods of volcanic activity explain 76 per cent of the simulated multidecadal variance in detrended 1860-2005 North Atlantic sea surface temperatures. After 1950, simulated variability is within observational estimates; our estimates for 1910-1940 capture twice the warming of previous generation models but do not explain the entire observed trend. Other processes, such as ocean circulation, may also have contributed to variability in the early twentieth century. Mechanistically, we find that inclusion of aerosol-cloud microphysical effects, which were included in few previous multimodel ensembles, dominates the magnitude (80 per cent) and the spatial pattern of the total surface aerosol forcing in the North Atlantic. Our findings suggest that anthropogenic aerosol emissions influenced a range of societally important historical climate events such as peaks in hurricane activity and Sahel drought. Decadal-scale model predictions of regional Atlantic climate will probably be improved by incorporating aerosol-cloud microphysical interactions and estimates of future concentrations of aerosols, emissions of which are directly addressable by policy actions.     

Analyses on the climate change responses over China under SRES B2 scenario using PRECIS

The global climate has been altered by the anthro- pogenic forcing due to greenhouse gases (GHGs) emis- sions. It is pointed out in the Third Assessments Report (TAR)[1] of Intergovernmental Panel on Climate Change (IPCC) in 2001 that over the 20th centur…     

马尾松分布格局对未来气候变化的响应

【目的】分析并预测未来气候变化对马尾松适宜分布范围,探讨影响马尾松潜在地理分布的主要气候因子,为马尾松潜在分布区种质资源管理和保护提供参考与指导。【方法】以中国数字植物标本馆记录的马尾松分布数据为基础,利用MaxEnt模型及地理信息系统ArcGIS 10.3软件探讨马尾松当前地理分布特征及其潜在分布区,并针对代表性浓度路径(RCP) 2.6及RCP 8.5两种气候情景下未来(2050年和2070年)马尾松适宜分布范围及主要气候因子进行分析。【结果】当前马尾松高适生区覆盖的地区主要分布于秦岭—淮河线以南。浙江、福建、江西、湖北西南部、湖南、重庆、四川东南部、贵州北部、广西中部、广东北部等地区为马尾松主要分布区,海南、云南及台湾等地为零星分布区。在未来气候情景下,马尾松适生区向我国北部地区迁移,包括河南西部、山东半岛、辽东半岛、河北东部、山西南部等地区,而在云南南部零星地区不会再有马尾松自然分布。在未来两种气候情景4个条件中,相同RCP情景下,不同年限各适生区之间的差异并不明显,变化趋势大致相同;但相同年限的不同RCP情景对应的各适生区面积变化存在明显区别,RCP 8.5的影响要高于RCP 2.6。影响马尾松地理分布的主导生物气候变量为年均降水量、最干月降水量及平均气温日较差,且降水较温度的影响更大。【结论】未来气候变化将导致马尾松分布范围进一步扩大,新增分布区主要集中于当前分布区北部。应以当前马尾松适生环境为基础,针对当地气候类型、土壤条件等环境因素合理建立保护区,以便马尾松能够顺利适应新环境。     

基于CMIP6集合优化数据集的全球陆地极端气候变化预估

预估极端气候事件趋势能够降低其引起的灾害风险.该文基于CMIP6集合优化数据集EPTGODD-WHU,选取5个极端气候指数,即最高气温极大值(TXx)、最高气温极小值(TXn)、最低气温极大值(TNx)、最低气温极小值(TNn)和最大月降水量(PXx),并结合GIS分析手段,对2021—2100年SSP1-2.6、SSP2-4.5和SSP5-8.5情景下的全球陆地极端气温及降水进行预估.结果表明：1)相较于CMIP单一模式,EPTGODD-WHU数据集模拟性能显著提升,气温及降水的空间相关系数分别达到0.99和0.81.2) SSP5-8.5情景下,年最低气温和最高气温均上升明显,且这种上升趋势年内波动不大,地球陆地极寒地区将面临升温的风险,而赤道等极热地区将处于年内长时间酷热状态.3)六大洲在SSP5-8.5情景下的极端降水整体上升趋势最剧烈,但北美洲密西西比平原和滨海平原的地区在SSP5-8.5情景下在未来面临较高的旱灾风险.4)中国西南部地区的极端降水在三个情景下均呈稳定的增幅,且增幅高达60%,预示面临较高的洪灾风险.     

Quantifying the risk of extreme seasonal precipitation events in a changing climate

Increasing concentrations of atmospheric carbon dioxide will almost certainly lead to changes in global mean climate. But because--by definition--extreme events are rare, it is significantly more difficult to quantify the risk of extremes. Ensemble-based probabilistic predictions, as used in short- and medium-term forecasts of weather and climate, are more useful than deterministic forecasts using a 'best guess' scenario to address this sort of problem. Here we present a probabilistic analysis of 19 global climate model simulations with a generic binary decision model. We estimate that the probability of total boreal winter precipitation exceeding two standard deviations above normal will increase by a factor of five over parts of the UK over the next 100 years. We find similar increases in probability for the Asian monsoon region in boreal summer, with implications for flooding in Bangladesh. Further practical applications of our techniques would be helped by the use of larger ensembles (for a more complete sampling of model uncertainty) and a wider range of scenarios at a resolution adequate to analyse average-size river basins.     

Influence of the carbon cycle on the attribution of responsibility for climate change

The carbon cycle is one of the fundamental climate change issues.Its long-term evolution largely affects the amplitude and trend of human-induced climate change,as well as the formulation and implementation of emission reduction policy and technology for stabilizing the atmospheric CO2concentration.Two earth system models incorporating the global carbon cycle,the Community Earth System Model and the Beijing Normal University-Earth System Model,were used to investigate the effect of the carbon cycle on the attribution of the historical responsibility for climate change.The simulations show that when compared with the criterion based on cumulative emissions,the developed(developing)countries’responsibility is reduced(increased)by 6%–10%using atmospheric CO2concentration as the criterion.This discrepancy is attributed to the fact that the developed world contributed approximately61%–68%(61%–64%)to the change in global oceanic(terrestrial)carbon sequestration for the period from 1850 to2005,whereas the developing world contributed approximately 32%–49%(36%–39%).Under a developed world emissions scenario,the relatively larger uptake of global carbon sinks reduced the developed countries’responsibility for carbon emissions but increased their responsibility for global ocean acidification(68%).In addition,the large emissions from the developed world reduced the efficiency of the global carbon sinks,which may affect the long-term carbon sequestration and exacerbate global warming in the future.Therefore,it is necessary to further consider the interaction between carbon emissions and the carbon cycle when formulating emission reduction policy.     

气候变化与海平面上升及其对海啸灾害的影响

综述了20世纪全球和中国气候变化的事实,预估了21世纪地表气温的可能变化,分析了由于气候变化引起的海平面上升和红树林、珊瑚礁等沿海生态系统被破坏的现状和未来演变趋势,重点分析了气候变化与海平面上升对海啸灾害的影响,并提出了对策措施。     

Extinction risk from climate change

Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.