Marine cloud brightening mitigates the warming induced by the aerosol reductions toward carbon neutrality

Abstract Marine cloud brightening (MCB), a geoengineering strategy that increases the cloud albedo, is potentially able to reduce the impacts of global warming. We simulate an MCB strategy to offset the warming induced by anthropogenic aerosol reduction following the Shared Socioeconomic Pathway 1-1.9 carbon-neutral scenario. Injecting sea salt aerosol into four cloudy regions in the eastern Pacific Ocean every year from 2020 to 2100 effectively restrains the future global-mean surface air temperature and precipitation change to the 2020 level. Aerosol-cloud interaction dominates the cooling in this MCB strategy. However, this strategy does not fully offset the warming in Europe, the United States, northeastern China and downwind offshore oceans, partly related to the acceleration of the Atlantic Meridional Overturning Circulation driven by the MCB-induced hemispherical asymmetric radiation gradients. Considering both the anthropogenic aerosol reductions and the MCB sea salt injection, some regions would face unintended climate change. Our study highlights the need for a more careful implementation strategy to produce both widespread cooling and fewer regional climate risks considering the effects are highly dependent on the strategy and seeding location.