The Southern Ocean Radiative Bias, Cloud Compensating Errors and Equilibrium Climate Sensitivity in CMIP6 Models
Alex Schuddeboom, Adrian McDonald
Abstract
Analysis of Coupled Model Intercomparison Project Phase 6 (CMIP6) models has focused on their higher equilibrium climate sensitivity (ECS) relative to CMIP5 simulations, with higher ECS values attributed to changing cloud feedbacks. We examine the simulation of the shortwave cloud radiative effect (SW CRE) in CMIP6 and explore a potential link between SW CRE errors and ECS. We derive mean and compensating errors in model data relative to satellite observations using a cloud clustering methodology. A statistically significant negative relationship between the mean and compensating errors in SW CRE over the Southern Ocean is identified. This relationship is observed elsewhere, but is only significant over the Southern Ocean. This implies model tuning efforts potentially hide biases in the representation of clouds in this region. High ECS models tend to have lower mean and compensating errors over the Southern Ocean, suggesting model biases are unlikely to explain the high ECS values.