Global Energy and Water Cycle Experiment GCSS Teams with CFMIP to Understand the Physical Mechanisms of Low Cloud Feedbacks in Climate Models

Despite progress in recent years in understanding cloud processes and feedbacks in General Circulation Models (GCMs; Bony et al., 2006; Stephens 2005), knowledge is lacking about the physical mechanisms of cloud feedbacks and the causes of model-to-model variation in simulated cloud feedbacks. These issues are related to several factors: (1) the transient and spatial variability of clouds is typically much larger than the small signal of cloud feedbacks; (2) clouds are highly interactive with atmospheric dynamical circulations; and (3) in a GCM, clouds are simulated with an interactive web of physical parameterizations of subgrid structure, microphysics, turbulent mixing, cumulus convection, radiation and surface fluxes, which are poorly resolved by the model grid.