Anthropogenic aerosols override greenhouse gases in Sahel climate change

Abstract Climate change has intensified weather extremes in the semi-arid Sahel, one of the world’s most vulnerable regions. However, the cause of the most dramatic changes, from the Sahel droughts of the 1970s and 1980s to wetter conditions in recent decades, remains contested. Here we use ensembles of climate model simulations to show that these changes were primarily driven by anthropogenic aerosols. Aerosol-induced slowdown of the Hadley Cell, the atmospheric circulation that drives tropical convection globally, caused the droughts. The subsequent reduction of aerosol emissions over the North Atlantic land regions enhanced meridional heating gradient, convection, and rainfall over the Sahel. Conversely, the impact of greenhouse gases is markedly weaker, 3.5 to 5.3 times less than that of aerosols. The discovery of a dominant role for the aerosol-induced heating gradient, rather than absolute concentrations, provides a framework for advancing regional climate risk assessments generally.