Impacts on polar climate by sea salt aerosol from blowing snow

Evidence from ice cores and atmospheric observations suggests that blowing saline snow on sea ice is a major source of sea salt aerosol in polar regions. This source is not represented in climate models but may have significant climate impacts. In addition to aerosol-radiation and -cloud interactions, sea salt aerosols release reactive halogens that destroy ozone and increase the atmospheric lifetime of methane. Sea salt aerosol produced from blowing snow in particular is smaller in size than sea salt from the open ocean rendering it more susceptible to long range transport. The fate of sea salt produced from blowing snow under climate change is unclear, as declining sea ice cover will tend to decrease emissions, while younger ice and thinner snow cover tend to increase emissions by increasing snow salinity. We simulate blowing snow sea salt aerosol under present and future climate scenarios within the Community Earth System Model (CESM2.1). We have implemented size-dependent blowing snow sea salt aerosol emissions into the 4-mode Modal Aerosol Model (MAM4) in the atmospheric component of CESM (CAM6). Simulated present-day sea salt aerosol concentrations are evaluated against surface, ship, and satellite observations. We calculate the radiative effects of blowing snow sea salt aerosol from aerosol-radiation interactions as well as aerosol effects on cloud properties, and present implications for our understanding of present-day polar climate and prediction of future climate. We find blowing snow sea salt aerosol results in large changes in wintertime cloud forcing in the Arctic, with smaller changes over Antarctica. We quantify the sensitivity of the modeled sea salt aerosol distribution and aerosol radiative effects to assumptions and uncertainties in meteorology, sub-grid processes, snowflake fragmentation, and surface snow salinity.