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On the Increase of Climate Sensitivity and Cloud Feedback With Warming in the Community Atmosphere Models
Author(s) -
Zhu Jiang,
Poulsen Christopher J.
Publication year - 2020
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl089143
Subject(s) - cloud feedback , climate sensitivity , shortwave , environmental science , climatology , atmospheric sciences , climate model , atmosphere (unit) , proxy (statistics) , climate state , latitude , middle latitudes , climate change , cloud computing , paleoclimatology , cloud fraction , global warming , radiative transfer , geology , cloud cover , meteorology , effects of global warming , geography , physics , oceanography , computer science , operating system , geodesy , quantum mechanics , machine learning
Modeling and paleoclimate proxy‐based studies suggest that equilibrium climate sensitivity (ECS) depends on the background climate state, though the reason is not thoroughly understood. Here we study the state dependence of ECS over a large range of global mean surface temperature (GMST) in the Community Atmosphere Model (CAM) Versions 4, 5, and 6 by varying atmospheric CO 2 concentrations. We find a robust increase of ECS with GMST in all three models, albeit at different rates, which is primarily attributed to strengthening of the shortwave cloud feedback ( λ cld ) at both high and low latitudes. Over high latitudes, increasing GMST leads to a reduction in the cloud ice fraction, weakening the (negative) cloud‐phase feedback due to the phase transition of cloud ice to liquid and thereby strengthening λ cld . Over low‐latitude regions, increasing GMST strengthens λ cld likely through the nonlinear increase in water vapor, which causes low‐cloud thinning through thermodynamic and radiative processes.