Tropical rainfall is important for regional climate around the globe.In a warming climate forced by rising CO2,the tropical rainfall will increase over the equatorial Pacific where sea surface warming is locally enhanced.Here,we analyze an idealized CO2 removal experiment from the Carbon Dioxide Removal Model Intercomparison Project(CDRMIP)and show that the tropical rainfall change features a stronger pattern during CO2 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 CO2 ramp-down increases over the equatorial Pacific with a southward extension,and decreases over the Pacific intertropical conver-gence zone and South Pacific convergence zone.The asymmetric rainfall changes between CO2 ramp-down and ramp-up result from time-varying contributions of the fast and slow oceanic responses to CO2 forcing,defined as the responses to abrupt CO2 forcing in the first 10 years and thereafter,respec-tively,in the abrupt-4xCO2 experiment.The fast response follows the CO2 evolution,but the slow response does not peak until 60 years after the CO2 peak.The slow response features a stronger El Nino-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 CO2 ramp-down.Our results indicate that returning the global mean temperature increase to below a cer-tain goal,such as 2℃,by removing CO2,may fail to restore tropical convection distribution,with poten-tially devastating effects on climate worldwide.

Shijie Zhou;Ping Huang;Shang-Ping Xie;Gang Huang;Lin Wang

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

科学通报（英文版）

[1]Shijie Zhou;Ping Huang;Shang-Ping Xie;Gang Huang;Lin Wang-.Varying contributions of fast and slow responses cause asymmetric tropical rainfall change between CO2 ramp-up and ramp-down)[J].科学通报（英文版）,2022(16):1702-1711

CDRMIP,intertropical,4xCO2

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