Revisiting the Impact of Sea Salt on Climate Sensitivity

Abstract

Abstract Recent laboratory and field studies point to an increase of sea salt aerosol (SSA) emissions with temperature, suggesting that SSA may lower climate sensitivity. We assess the impact of a strong (4.2% K −1) and weak (0.7% K −1) temperature response of SSA emissions on the climate sensitivity of the coupled climate model CM4. We find that the stronger temperature dependence improves the simulation of marine aerosol optical depth sensitivity to temperature and lowers CM4 Transient Climate Response (‐0.12 K) and Equilibrium Climate Sensitivity (‐0.5 K). At CO2 doubling, the higher SSA emission sensitivity causes a negative radiative feedback (‐0.125 Wm−2K−1), which can only be partly explained by changes in the radiative effect of SSA (‐0.08 Wm−2K−1). Stronger radiative feedbacks are dominated by more negative low‐level cloud feedbacks in the Northern Hemisphere, which are partly offset by more positive feedbacks in the Southern Hemisphere associated with a weaker Atlantic Meridional Overturning Circulation.