PNNL

Abstract

Aerosol-cloud interactions (ACI) in warm clouds are the primary source of uncertainty in effective radiative forcing (ERF) during the historical period and, by extension, in-ferred climate sensitivity. The ERF due to ACI (ERFaci) is composed of the radiative forcing due to changes in cloud microphysics (RFaci) and cloud adjustments to microphysics. Here, we examine the processes that drive ERFaci using a perturbed parameter ensemble (PPE) hosted in CAM6. Examination of cloud and radiation processes in the PPE reveal buffering of ERFaci by the interaction of precipitation efficiency and radiative susceptibility. We find that PPE members with lower precipitation efficiency have a larger present day (PD) LWP as well as a larger LWP adjustment. However, larger PD LWP also results in PPE members that are closer to radiative saturation and a smaller effect from LWP adjustments on ERFaci. It is likely that the buffering diagnosed in CAM6 is present in other ESMs.