Larger Cloud Liquid Water Enhances Both Aerosol Indirect Forcing and Cloud Radiative Feedback in Two Earth System Models

Abstract

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, reasons for this anti‐correlation are less explored. In this study, we perturb the cloud ice microphysical processes to obtain cloud liquid of varying amounts in two Earth System Models (ESMs). We find 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. 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. This work, from a cloud state perspective, emphasizes the influence of the mean‐state LWP on effective radiative forcing due to ACI (ERFACI).

Buffering of Aerosol‐Cloud Adjustments by Coupling Between Radiative Susceptibility and Precipitation Efficiency

“…The result is the opposite from what has been found by Zhao et al (2024). In Zhao et al (2024), cloud physics parameters that are important to ice processes are perturbed. Models with weaker ice production processes tend to simulate more LWP as well as stronger (more negative) ERFaci.…”

“…At higher ΔN d(PD PI) (>10 cm 3 ), larger ΔLWP (PD PI ) correlates with weaker ERFaci. The result is the opposite from what has been found by Zhao et al (2024). In Zhao et al (2024), cloud physics parameters that are important to ice processes are perturbed.…”

“…In the CAM6 PPE, in addition to perturbing ice processes, liquid processes, convection, and aerosol processes that are important to ACI are also perturbed (Table S1 in Supporting Information S1). We find that parameters associated with rain processes (Khairoutdinov & Kogan, 2000) dominate the cloud liquid amount in liquid cloud, while in Zhao et al (2024) the mean-state LWP in mix-phase cloud is driven by perturbations to ice processes.…”