Intermodel compensation between cloud feedback and aerosol indirect effect in CMIP6

Abstract:

The new generation of climate models includes estimates of effective climate sensitivity (ECS) that are much higher than past generations due to stronger amplification from cloud feedbacks. If plausible, these models require substantially larger greenhouse gas reductions to meet warming targets. We show that models with stronger cloud feedback also have a stronger cooling effect from cloud-aerosol interactions. These two effects offset each other during the historical period when both aerosols and greenhouse gases increase, allowing both strong and weak cloud feedback models to reproduce the observed global-mean temperature change during the 20^th Century. Aerosol-cloud interaction produce a distinct asymmetry in the interhemispheric pattern of warming, and the compensation between cloud feedback and aerosol-cloud interactions may result from model tuning, or be an intrinsic cloud-circulation response to the hemispheric asymmetry in warming. We show that the observed warming asymmetry is more consistent with the low ECS/aerosol indirect effect models.