Anthropogenic aerosols (AAs) exert the strongest anthropogenic influence on climate after carbon dioxide. However, the AA radiative forcing is poorly constrained compared to the carbon dioxide radiative forcing because it depends on processes which are weakly observationally constrained and therefore have a range of representations among earth system models. I will present work from two projects that aim to improve understanding of AA forcing. First, I will explore how the climate of the Canadian Earth System Model (CanESM) and its response to AA forcing depend on the representation of aerosol microphysics. Specifically, I will discuss the development of a new more detailed aerosol module for CanESM. I will show how the module was tuned and compare its climate and response to AA forcing to the existing aerosol module’s. Second, I will present the Regional Aerosol Model Intercomparison Project (RAMIP) simulations, which are designed to isolate the effect of near-term aerosol emissions reductions from different regions. I will show that the radiative forcing associated with emissions reductions is different in CanESM than in other models, and outline my plan to elucidate the differences in aerosol-cloud interactions among the RAMIP models.