摘要
Tropical rainfall is important for regional climate around the globe.In a warming climate forced by rising CO_(2),the tropical rainfall will increase over the equatorial Pacific where sea surface warming is locally enhanced.Here,we analyze an idealized CO_(2) removal experiment from the Carbon Dioxide Removal Model Intercomparison Project(CDRMIP)and show that the tropical rainfall change features a stronger pattern during CO_(2) ramp-down than ramp-up,even under the same global mean temperature increase,such as the 2℃ goal of the Paris Agreement.The tropical rainfall during CO_(2) ramp-down increases over the equatorial Pacific with a southward extension,and decreases over the Pacific intertropical convergence zone and South Pacific convergence zone.The asymmetric rainfall changes between CO_(2) ramp-down and ramp-up result from time-varying contributions of the fast and slow oceanic responses to CO_(2) forcing,defined as the responses to abrupt CO_(2) forcing in the first 10 years and thereafter,respectively,in the abrupt-4xCO_(2) experiment.The fast response follows the CO_(2) evolution,but the slow response does not peak until 60 years after the CO_(2) peak.The slow response features a stronger El Niño-like pattern,as the ocean dynamical thermostat effect is suppressed under stronger subsurface warming.The delayed and stronger slow response leads to stronger tropical rainfall changes during CO_(2) ramp-down.Our results indicate that returning the global mean temperature increase to below a certain goal,such as 2℃,by removing CO_(2),may fail to restore tropical convection distribution,with potentially devastating effects on climate worldwide.
热带降水异常可通过影响大气环流的变化进而对全球以及区域气候产生重要的影响,因此全球变暖引起的热带降水变化受到广泛的关注.过去研究表明在CO_(2)浓度上升导致的全球变暖下,热带降水将会在赤道太平洋海温增加较多的区域增加.本研究分析了CO_(2)移除模式比较计划中的理想化的CO_(2)移除试验,发现即便在同等的全球平均增温下,CO_(2)浓度下降期的热带降水变化明显比CO_(2)浓度上升期强.这种非对称的降水变化是由快慢两种时间尺度的海洋响应所导致,其中快响应贡献随时间的变化基本与CO_(2)浓度的变化一致,而慢响应的贡献则在CO_(2)浓度达到峰值下降60年后才达到峰值.同时,慢响应下热带海洋次表层增温较快抑制了海洋恒温器效应,使得赤道东太平洋地区形成了更强的类厄尔尼诺型增暖,因而能引起较强的热带降水变化.海洋滞后的慢响应及其引起的较强热带降水变化导致了热带降水在CO_(2)浓度上升期和下降期呈非对称变化.结果表明:未来即便通过CO_(2)移除等方式让全球平均增温恢复到一个较低的既定目标,如巴黎协定的2℃增温目标,热带对流降水的分布也可能与CO_(2)浓度上升期存在较大差异,可引起更大的全球气候异常.
作者
Shijie Zhou
Ping Huang
Shang-Ping Xie
Gang Huang
Lin Wang
周士杰;黄平;谢尚平;黄刚;王林(Center for Monsoon System Research,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100190,China;State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029,China;Scripps Institution of Oceanography,University of California San Diego,La Jolla CA 92093,USA;Laboratory for Regional Oceanography and Numerical Modeling,Pilot National Laboratory for Marine Science and Technology,Qingdao 266237,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)
基金
supported by the National Key Research&Development Program of China(2019YFA0606703)
the National Natural Science Foundation of China(41975116 and 42105027)
the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Y202025)
the China Postdoctoral Science Foundation(BX20200329 and 2020M680646)
the Special Research Assistant Project of Chinese Academy of Sciences。
