Uncertainty in crossing time of 2 °C warming threshold over China
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The 2 °C warming target has been used widely in global and regional climate change research. Previous studies have shown large uncertainties in the time when surface air temperature (SAT) change over China will reach 2 °C relative to the pre-industrial era. To understand the uncertainties, we analyzed the projected SAT in the twenty-first century using 40 state-of-the-art climate models under two Representative Concentration Pathways (RCP4.5 and RCP8.5) from the Coupled Model Intercomparison Project Phase 5. The 2 °C threshold-crossing time (TCT) of SAT averaged across China was around 2033 and 2029 for RCP4.5 and RCP8.5, respectively. Considering a ±1σ range of intermodel SAT change, the upper and lower bounds of the 2 °C TCT could differ by about 25 years or even more. Uncertainty in the projected SAT and the warming rate around the TCT are the two main factors responsible for the TCT uncertainty. The former is determined by the climate sensitivity represented by the global mean surface temperature response. About 45 % of the intermodel variance of the projected 2 °C TCT for averaged SAT over China can be explained by climate sensitivity across the models, which is contributed mainly by central and southern China. In a climate more sensitive to CO2 forcing, stronger greenhouse effect, less stratus cloud over the East Asian monsoon region, and less snow cover on the Tibetan Plateau result in increased downward longwave radiation, increased shortwave radiation, and decreased shortwave radiation reflected by the surface, respectively, all of which may advance the TCT.
Keywords2 °C threshold Projection uncertainty China region CMIP5 Climate sensitivity
关键字2°C阈值 预估不确定性 中国地区 耦合模式比较计划 气候敏感度
We thank three anonymous reviewers for their constructive suggestions for improving this study. This work was supported jointly by the “Strategic Priority Research Program–Climate Change: Carbon Budget and Related Issues” of the Chinese Academy of Sciences (XDA05110300), the Research Fund for Commonwealth Trades (Meteorology) (GYHY201506012), the National Natural Science Foundation of China (41420104006), and the China Postdoctoral Science Foundation (2015M581152). We acknowledge the climate modeling groups for making available their model output (http://cmip-pcmdi.llnl.gov/cmip5/availability.html) and the World Climate Research Program’s (WCRP’s) Working Group on Coupled Modeling (WGCM) which coordinates the CMIP5 project.
Conflict of interest
The authors declare that they have no conflict of interest.
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