气候变化的归因和预估模拟研究

Progress in Climate Change Attribution and Projection Studies

本文总结了近五年来中国科学院大气物理研究所在气候变暖的归因模拟与预估研究上的主要进展。研究表明,利用海温、太阳辐射和温室气体等实际强迫因子驱动大气环流模式,能够较为合理地模拟全球平均地表气温在20世纪的演变,但是难以模拟出包括北大西洋涛动/北极涛动和南极涛动在内的高纬度环流的长期变化趋势。利用温室气体和硫酸盐气溶胶等"历史资料"驱动气候系统模式,能够较好地模拟出20世纪后期的全球增暖,但如果要再现20世纪前期(1940年代)的变暖,还需同时考虑太阳辐射等自然外强迫因子。20世纪中国气温演变的耦合模式模拟技巧,较之全球平均情况要低;中国气候在1920年代的变暖机理目前尚不清楚。对于近50年中国东部地区"南冷北暖"、"南涝北旱"的气候变化,基于大气环流模式特别是区域气候模式的数值试验表明,夏季硫酸盐气溶胶的负辐射效应超过了温室气体的增暖效应,从而对变冷产生贡献。但现有的数值模拟证据,不足以说明气溶胶增加对"南涝北旱"型降水异常有贡献。20世纪中期以来,青藏高原主体存在明显增温趋势,温室气体浓度的增加对这种增暖有显著贡献。多模式集合预估的未来气候变化表明,21世纪全球平均温度将继续增暖,增温幅度因不同排放情景而异;中国大陆年均表面气温的增暖与全球同步,但增幅在东北、西部和华中地区较大,冬季升温幅度高于夏季、日最低温度升幅要强于日最高温度;全球增暖有可能对我国中东部植被的地理分布产生影响。伴随温室气体增加所导致的夏季平均温度升高,极端温度事件增多;在更暖的气候背景下,中国大部分地区总降水将增多,极端降水强度加大且更频繁发生,极端降水占总降水的比例也将增大。全球增暖有可能令大洋热盐环流减弱,但是减弱的幅度因模式而异。全球增暖可能不是导致北太平洋副热带-热带经圈环流自20世纪70年代以来变弱的原因。文章同时指出了模式预估结果中存在的不确定性。

This paper summarizes the progress of climate change attribution and projection modeling studies achieved by scientists in the Institute of Atmospheric Physics, Chinese Academy of Sciences, over recent five years. When forced by a combination of sea surface temperature, solar radiation, and green houses gases, the atmospheric general circulation models can reasonably reproduce the evolution of global mean surface air temperature （SAT） during the 20th century, however, fail in capturing the long term trend of high latitude circulations measured by the North Atlantic Oscillation/Arctic Oscillation, or Antarctic Oscillation index. Examinations on the variations of SAT over China and the globe in the 20th century simulated by 19 coupled climate models of IPCC AR4 driven by historical natural and anthropogenic forcing agents show that most models perform well in simulating both the global and northern hemispheric mean SAT evolutions. The inclusion of natural forcing agents improves the simulation, in particular for the first half of the century. The reproducibility of the SAT averaged over China is lower than that of the global and hemispheric averages, but it is still acceptable. No model could successfully reproduce the reconstructed warming over China in the 1920s, which indicates that the mechanism responsible for the 1920s warming remains to be an open question. Numerical simulations employing AGCMs and regional climate models suggest that the negative radiation effects of sulfate aerosol overlap the effects of greenhouse gases and hence contribute to the surface cooling over eastern China during summer. However, there are no evidences supporting the idea that the anthropogenic aerosol emission dominates the recent ＂Southern Flooding and Northern Drought＂ rainfall pattern in eastern China. Observational evidences indicate a warming trend of SAT over the Tibetan Plateau starting from the middle of the 20th century. Climate model results suggest that the increase of greenhouse gases contributes to this warming trend. Multi-model ensemble scenario projections of future climate change during the 21st century indicate that the global mean SAT would continue to rise in the forthcoming century, while the intensities are scenario-dependent. The potential warming of annual mean SAT over continental China generally parallels that of the global average. The amplitudes over Northeast China, western China, and central China are stronger than that over the other regions. The warming during winter would be stronger than that during summer; the increase of daily minimum temperature would be larger than that of daily maximum temperature. Numerical model results also suggest that the global warming might have impacts on the geographic distribution of vegetations over the middle and eastern China. Analysis on the output of IPCC AR4 scenario projections shows that following the summertime warming, both the intensity and frequency of extreme precipitation and temperatures would increase over China. Multi-model inter-comparison indicates that the global warming might lead to a weakening of the thermohaline circulation; however, the change of intensity is model-dependent. Numerical model results also suggest that the global warming might not be a mechanism responsible for the recent weakening of the North Pacific shallow meridional subtropical-tropical cell observed since the late 1970s. Uncertainties in future climate change model projections are also emphasized.