Climate Change of 4°C Global Warming above Pre-industrial Levels
Using a set of numerical experiments from 39 CMIP5 climate models, we project the emergence time for 4◦C global warming with respect to pre-industrial levels and associated climate changes under the RCP8.5 greenhouse gas concentration scenario. Results show that, according to the 39 models, the median year in which 4◦C global warming will occur is 2084. Based on the median results of models that project a 4◦C global warming by 2100, land areas will generally exhibit stronger warming than the oceans annually and seasonally, and the strongest enhancement occurs in the Arctic, with the exception of the summer season. Change signals for temperature go outside its natural internal variabilities globally, and the signal-tonoise ratio averages 9.6 for the annual mean and ranges from 6.3 to 7.2 for the seasonal mean over the globe, with the greatest values appearing at low latitudes because of low noise. Decreased precipitation generally occurs in the subtropics, whilst increased precipitation mainly appears at high latitudes. The precipitation changes in most of the high latitudes are greater than the background variability, and the global mean signal-to-noise ratio is 0.5 and ranges from 0.2 to 0.4 for the annual and seasonal means, respectively. Attention should be paid to limiting global warming to 1.5◦C, in which case temperature and precipitation will experience a far more moderate change than the natural internal variability. Large inter-model disagreement appears at high latitudes for temperature changes and at mid and low latitudes for precipitation changes. Overall, the intermodel consistency is better for temperature than for precipitation.
Key words4°C global warming timing climate change signal-to-noise ratio uncertainty
使用39个CMIP5模式的试验数据, 预估了在RCP8.5情景下相对于工业革命前期4℃全球变暖发生的时间以及相应的全球温度和降水变化. 39个模式的中位数显示4℃全球变暖将发生在2084年, 其中有29个模式预估在21世纪全球达到4℃升温. 全球变暖4℃背景下, 年和季节增温在陆地高于海洋; 除夏季外, 最强增温发生在北极. 年和季节温度增幅均超过其自然内部变率, 全球平均的年和季节温度变化的信噪比分别为9.6和6.3~7.2, 其中最大值出现在低纬地区. 降水主要表现为在副热带减少, 在高纬增幅较大并超过其自然内部变率; 全球平均的年和季节降水变化的信噪比分别为0.5和0.2~0.4. 总体上, 多模式预估的温度变化有较高的一致性, 降水变化的不确定性较大, 特别是在中纬和低纬地区.
关键词4℃全球变暖 时间 气候变化 信噪比 不确定性
We sincerely thank the three anonymous reviewers for their insightful comments and suggestions to improve this manuscript. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups for producing and making available their model output. For CMIP, the U.S. Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. This research was supported by the National Basic Research Program of China (Grant No. 2016YFA0602401) and the National Natural Science Foundation of China (Grant No. 41421004).
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