Sea‐salt injections into the low‐latitude marine boundary layer: The transient response in three Earth system models

Abstract

AbstractAmong proposed mechanisms for counteracting global warming through solar radiation management is the deliberate injection of sea salt acting via marine cloud brightening and the direct effect of sea‐salt aerosols. In this study, we show results from multidecadal simulations of such sea‐salt climate engineering (SSCE) on top of the RCP4.5 emission scenario using three Earth system models. As in the proposed “G3” experiment of the Geoengineering Model Intercomparison Project, SSCE is designed to keep the top‐of‐atmosphere radiative forcing at the 2020 level for 50 years. SSCE is then turned off and the models run for another 20 years, enabling an investigation of the abrupt warming associated with a termination of climate engineering (“termination effect”). As in former idealized studies, the climate engineering in all three models leads to a significant suppression of evaporation from low‐latitude oceans and reduced precipitation over low‐latitude oceans as well as in the storm‐track regions. Unlike those studies, however, we find in all models enhanced evaporation, cloud formation, and precipitation over low‐latitude land regions. This is a response to the localized cooling over the low‐latitude oceans imposed by the SSCE design. As a result, the models obtain reduced aridity in many low‐latitude land regions as well as in southern Europe. Terminating the SSCE leads to a rapid near‐surface temperature increase, which, in the Arctic, exceeds 2 K in all three models within 20 years after SSCE has ceased. In the same period September Arctic sea ice cover shrinks by over 25%.