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Attributions of Equilibrium Climate Sensitivity change from FGOALS-g2 to FGOALS-g3
He Wang, Lijuan Li, Xiaolong Chen, Bin Wang
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), IAP.
Equilibrium climate sensitivity (ECS) and its related feedbacks are important metrics to measure the temperature increases in the future scenario projections. Based on the radiative kernel approach with simplified cloud feedback calculation, the ECS and its feedbacks are analyzed between two versions of the Flexible Global Ocean-Atmosphere-Land System model grid-point (FGOALS-g3 and FGOALS-g2), participating in the Fifth and Sixth Phase of Coupled Model Intercomparison Project (CMIP5 and CMIP6) respectively. Results show that the ECS of FGOALS-g3 is smaller than that of FGOALS-g2 (2.8 K versus 3.3 K). The main feedbacks contributing to the ECS change include the decreased surface albedo feedback and increased cloud negative feedback in FGOALS-g3. The reduced surface albedo feedback in FGOALS-g3 is mainly associated with its basic mean state, such as the lower surface air temperature (SAT) and more sea ice area (SIA) when compared to those in FGOALS-g2. The enhanced cloud negative feedback in FGOALS-g3 is mainly associated with its higher low cloud area fraction (CAF) and liquid water path (LWP). Further, the ECS change is traced back to the upgraded cloud parameterization scheme, parameter tuning, ocean grids and external forcings in FGOALS-g3 which affect to simulate the different climate mean state.