Previous studies have noticed that the Coupled Model Intercomparison Project Phase 6 (CMIP6) models with a stronger cooling from aerosol-cloud interactions (ACI) (ERF_ACI) also have an enhanced warming from positive cloud feedback, and these two opposing effects are counter-balanced in simulations of the historical period. However, reasons for this anti-correlation between cloud feedback and ERF_ACI are less explored.

In this study, we investigate this anti-correlation through both warm rain and ice microphysical processes using the two Earth System Models: the DOE’s Energy Exascale Earth System Model version 2 (E3SMv2) and the NCAR Community Earth System Model version 2 (CESM2). First, we perturb the autoconversion process in the two models and find that higher autoconversion rates which are associated with stronger ERF_ACI suppress the increase in cloud liquid water path (LWP) during global warming, thereby curtailing the rise in cloud optical depth, resulting in a diminished negative shortwave effect that contributes to intensified positive total cloud feedback. On the other hand, we perturb the cloud ice microphysical processes in the two models to obtain cloud liquid of varying amounts. We find that the model simulations with a larger LWP tend to have a stronger cooling from ACI and a stronger positive cloud feedback during warming. More liquid clouds in the mean-state present more opportunities for anthropogenic aerosol perturbations and also weaken the negative cloud feedback at middle to high latitudes. Our study offers new insights into the compensatory mechanisms between ERF_ACI and cloud feedback through both warm- and ice-phase cloud microphysics. Future work should focus on constraining modeled LWP from observations to reduce the uncertainties in both ERF_ACI and cloud feedback.