Among models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6), here we show that the magnitude of the tropical low cloud feedback, which contributes considerably to uncertainty in estimates of climate sensitivity, is intimately linked to tropical deep convection and its effects on the tropical atmospheric overturning circulation. First, a reduction in tropical ascent area and an increased frequency of heavy precipitation result in high cloud reduction and upper-tropospheric drying, which increases longwave cooling and reduces subsidence weakening, favoring low cloud reduction (Radiation-Subsidence Pathway). Second, increased longwave cooling decreases tropospheric stability, which also reduces subsidence weakening and low cloudiness (Stability-Subsidence Pathway). In summary, greater high cloud reduction and upper-tropospheric drying (negative longwave feedback) lead to a more positive cloud feedback among CMIP6 models by contributing to a greater reduction in low cloudiness (positive shortwave feedback). Varying strengths of the two pathways contribute considerably to the intermodel spread in climate sensitivity.
Bibliographical noteFunding Information:
Co-Author Jonathan H. Jiang acknowledge the support by the Jet Propulsion Laboratory, California Institute of Technology, under contract by NASA. HS, FA, ND, and JDN acknowledge funding support by the DOE-RGMA program (DE‐SC0021312) and NOAA-MAPP (NA20OAR4310394). KAS, HS, and JHJ also gratefully acknowledge NASA funding for CMIP6 climate model analysis and evaluation using NASA data, as well as funding from the NASA ROSES MAP and TASNPP programs. CES acknowledges support from NSF Graduate Research Fellowship under Grant No. DGE-1745301. GSE is supported by the NASA Modeling, Analysis and Prediction (MAP), Precipitation Measurement Missions (Grant #80NSSC22K0609), and Terra, Aqua, and Suomi NPP (Grants #80NSSC18K1030 and #80NSSC21K1978) Programs. The authors thank Joyce Meyerson for graphical assistance with Fig. .
© 2022, The Author(s).