Increasing Precipitation Efficiency Amplifies Climate Sensitivity by Enhancing Tropical Circulation Slowdown and Eastern Pacific Warming Pattern

Abstract

The role of precipitation efficiency (PE)—the fraction of column-integrated condensate that reaches the surface as rain—in the global temperature response to CO2 rise is yet to be quantified. Here we employ 36 limited-domain cloud resolving models (CRMs) from the Radiative-Convective Equilibrium Model Intercomparison Project and find that they strongly imply higher PE at warmer temperatures. We then analyze 35 general circulation models (GCMs) from the Coupled Model Intercomparison Project Phase 6 and find that increasing PE is associated with tropical circulation slowdown and greater eastern equatorial Pacific warming. These changes trigger pan-tropical positive cloud feedback through stratiform anvil cloud reduction and stratocumulus suppression, resulting in higher Effective Climate Sensitivity (ECS). We find that in 24 of 35 GCMs matching the CRMs in simulating increasing PE with greenhouse warming, mean ECS is 1 K higher than in PE-decreasing GCMs. Thus, further constraining PE sensitivity to temperature could reduce uncertainty over future climate projections.