Subtropical Marine Cloud Brightening Suppresses the El Niño–Southern Oscillation

Abstract Stratospheric aerosol injection (SAI) and marine cloud brightening (MCB) are two proposed methods of compensating for greenhouse gas‐induced warming by reflecting incoming solar radiation. However, their effects on the El Niño–Southern Oscillation (ENSO), a critical mode of climate variability, are poorly understood. Here we use ensembles of climate model simulations to show that deploying MCB in the subtropical eastern Pacific dramatically reduces ENSO amplitude by approximately 61%, while SAI has a negligible impact. MCB increases cloud albedo, which cools the subtropical eastern Pacific and triggers a loss of moist static energy. This cooling promotes atmospheric subsidence, dries the tropical Pacific, and intensifies the trade winds. The ultimate effect is a dramatic reduction in all air‐sea feedback processes operating during ENSO, which we demonstrate using a mixed‐layer heat budget. This contrast between the MCB and SAI impacts on ENSO shows that the choice of climate intervention strategy used to mitigate global warming has drastic regional implications.