Understanding projected uncertainty of Southern Ocean sea salt aerosol in CESM1-LE: role of internal variability

Abstract Southern Ocean (SO) sea salt aerosol is key to Earth’s energy budget, but its future changes are highly uncertain. Here using a 40-member ensemble from the Community Earth System Model Large Ensemble (CESM1-LE) project, we find that projected SO sea salt is modulated by internal climate variability both locally in the SO and remotely from the tropical Pacific. The leading mode of inter-member diversity displays a zonally homogenous pattern associated with the Southern Annular Mode due to its impact on future westerly poleward intensification. The second largest source of inter-member uncertainty relates to El Niño-Southern Oscillation (ENSO). In particular, as El Niño and La Niña are not symmetric, the cumulative ENSO impact on SO winds exhibits a meridional dipole in the south Pacific, such that a stronger future ENSO with more extreme El Niño events will induce a larger zonally heterogenous distribution of SO sea salt. Our results uncover an important role of ENSO nonlinearity in projected SO sea salt aerosol distribution.