Larger Cloud Liquid Water Enhances Both Aerosol Indirect Forcing and Cloud Radiative Feedback in Two Earth System Models
Previous studies have noticed that the Coupled Model Intercomparison Project Phase 6 (CMIP6) models with a stronger cooling from aerosol-cloud interactions (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, the reasons for the relationship between cloud feedback and ERFACI have not been explored.
In this study, researchers perturb the ice microphysical processes to obtain cloud liquid of varying amounts in DOE E3SMv2 and NCAR CESM2. They found that the model simulations with a larger liquid water path (LWP) tend to have a stronger cooling from ACI and a stronger positive cloud feedback. This work also points out the influence of the mean-state LWP on ERFACI, which is different from most previous studies that investigated the aerosol influence on ERFACI.
Cloud feedback and effective radiative forcing due to aerosol-cloud interactions (ERFACI) are two critical factors for understanding the past and projecting the future climate change. In this study, researchers found that both the aerosol ERFACI and cloud feedback are modulated by mean-state LWP. The warming induced by cloud feedback and cooling by ACI counteracts each other. The mean-state LWP is an important factor influencing both the ERFACI and cloud feedback, and is a useful index for the future climate projection. This study suggests the importance of better constraining the modeled LWP with observations to reduce the uncertainties of cloud feedback and aerosol ERFACI.
Cloud feedback and effective radiative forcing due to aerosol-cloud interactions (ERFACI) are two critical factors for understanding the past and projecting the future climate change. The Coupled Model Intercomparison Project Phase 6 (CMIP6) models with a stronger ERFACI cooling also have an enhanced warming from positive cloud feedback. However, the reasons for the relationship have not been explored. Through model experiments with E3SMv2 and CESM2, this study found that ERFACI strengthens with the increase of mean-state LWP, while cloud feedback increases with the increase of mean-state LWP. Both cloud feedback and ERFACI are influenced by LWP. Future work should focus on improving modeled LWP to reduce the uncertainties in both ERFACI and cloud feedback.