Aerosols have significant impacts on climate by altering the radiative balance of the atmosphere through interactions with radiation and clouds. Anthropogenic aerosols lead to an overall cooling effect (aerosol dimming), partially offsetting the warming caused by greenhouse gases (GHGs). However, recent declines in aerosol emissions due to air quality regulations have weakened this cooling effect, making the warming effect of GHGs more pronounced. To accurately attribute past climate changes and improve future climate projections in the Energy Exascale Earth System Model (E3SM), it is crucial to evaluate the historical evolution of aerosol distributions and the associated anthropogenic forcing.

Driven by its overarching science objectives, the E3SM model has been developed through three major versions, each with distinct simulations of aerosol characteristics. From version 1 to version 2, substantial tuning of clouds and convection in the atmosphere model significantly impacted the simulated aerosol lifetime, despite the aerosol parameterizations remaining nearly the same as in version 1. In contrast, version 3 introduced significant changes to aerosol parameterizations, including secondary organic aerosol treatment, wet removal, process coupling, natural aerosol production, and atmospheric chemistry. These changes, combined with additional tuning related to aerosol-cloud interactions, led to a much lower anthropogenic aerosol burden and radiative forcing compared to version 2.

Following the CMIP6 protocol, we use pre-industrial, historical, and single-forcing coupled simulations, as well as atmosphere-only simulations, to compare the simulated aerosol distributions, radiative forcing, and their impacts on climate across the three E3SM versions. Additionally, we will examine the relationship between aerosol forcing and climate feedback in E3SM through idealized experiments.