Does model resolution matter for the estimate of aerosol-cloud interactions?

Successful simulations of aerosol-cloud interactions (aerosol indirect effects) in general circulation models (GCMs) require accurate representations of small-scale aerosol and cloud-related processes. The parameterizations of such sub-grid processes are generally model resolution dependent, which suggests that the estimate of aerosol indirect effects could potentially be impacted by model resolution.

In this study, we conducted climatological simulations with two GFDL atmospheric GCM: AM3 and AM3-CLUBB (Cloud Layer Unified By By-normal), and estimated aerosol radiative forcing at different model horizontal resolution. We find that the total aerosol forcing is dominated by sulfate aerosol forcing, and the magnitudes of the sulfate forcing decrease at higher model resolution in both AM3 and AM3-CLUBB. Further investigation shows that sulfate burden is reduced at higher resolution, and this reduction seems to be more significant in polluted regions such as East Asia, leading to less negative (anthropogenic) sulfate forcing.

The decrease of the magnitudes of aerosol forcing with resolution would alleviate the likely overestimate of aerosol forcing in the GFDL GCMs and shared by many state-of-the-art GCMs, and potentially mitigate the under-prediction of the 20th century warming. Therefore it could have important implications for future climate projection.