Assessing the impact of anthropogenic aerosols in a kilometer-scale Earth system model

Aerosols influence Earth's climate directly by scattering or absorbing radiation and indirectly by serving as nuclei for cloud droplets or ice crystals. Earth system models have significantly improved our understanding of aerosols, clouds, and radiation. The resolution of these models has increased from above 100 kilometers to below 10 kilometers in recent years. With that, important atmospheric processes like deep convective motions are explicitly resolved.

To perform kilometer-scale (km-scale) simulations with the Earth system model ICON-MPIM, we developed the one-moment aerosol module HAM-lite. In HAM-lite, aerosols are represented as an ensemble of log-normal modes with prescribed properties. There are two pure modes, one composed of dust and one composed of sea salt, and two internally mixed modes, both composed of organic carbon, black carbon, and sulfate. The first mixed mode includes aerosols from biomass burning emissions and the second mixed mode includes aerosols from anthropogenic and volcanic emissions. The four modes are transported through the atmosphere and are coupled with various processes such as radiation, convection, and precipitation.

To assess the impact of anthropogenic aerosols, we performed two km-scale simulations over one year with different emission scenarios. The present-day scenario is based on emissions from the Community Emissions Data System (CEDS) and the Global Fire Assimilation System (GFAS). The pre-industrial scenario is based on the historic biomass burning emissions for CMIP6 (BB4CMIP). In both simulations, the sea surface temperature and sea ice are prescribed with the boundary conditions of AMIP, and the initial conditions of the atmosphere and land are derived from the operational analysis of ECMWF. Based on these two scenarios, we analyze how anthropogenic aerosols interact with radiation and clouds over one year.