Extratropical Shortwave Cloud Feedbacks in the Context of the Global Circulation and Hydrological Cycle
Daniel T. McCoy, Paul R. Field, Michelle Frazer, Mark D. Zelinka, Gregory S. Elsaesser, Johannes Mülmenstädt, Ivy Tan, Timothy A. Myers, Zachary J. Lebo
Abstract
Abstract Shortwave (SW) cloud feedback (SW FB ) is the primary driver of uncertainty in the effective climate sensitivity (ECS) predicted by global climate models (GCMs). ECS for several GCMs participating in the sixth assessment report exceed 5K, above the fifth assessment report “likely” maximum (4.5K) due to extratropical SW FB 's that are more positive than those simulated in the previous generation of GCMs. Here we show that across 57 GCMs Southern Ocean SW FB can be predicted from the sensitivity of column‐integrated liquid water mass (LWP) to moisture convergence and to surface temperature. The response of LWP to moisture convergence and the response of albedo to LWP anti‐correlate across GCMs. This is because GCMs that simulate a larger response of LWP to moisture convergence tend to have higher mean‐state LWPs, which reduces the impact of additional LWP on albedo. Observational constraints suggest a modestly negative Southern Ocean SW FB — inconsistent with extreme ECS.