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Anthropogenic aerosols dominate forced Sahel precipitation variability through distinct atmospheric and oceanic drivers

Throughout the 20th century, the Sahel region of Northern Africa underwent drastic multidecadal climate variations, with substantial impacts on the populations of the region. Concurrently, there has been substantial changes in atmospheric composition due to a wide array of anthropogenic emission sources, which may have played a role in causing this variability. In particular, we examine the potential role of anthropogenic aerosols (AA), such as sulfates and black carbon. Using two large ensembles of global coupled model (GCM) simulations we find that aerosols drive multidecadal precipitation variability that is similar in phase, but is smaller in magnitude to observed Sahel precipitation variability.

Using additional atmosphere-land GCM (AGCM) simulations, we decompose the multidecadal response to AAs into the component that is directly due to the aerosol forcing and the component that is due to subsequent aerosol forced sea surface temperature (SST) anomalies. We find that the direct atmospheric response is the primary driver of drying between the 1950s and 1970s, while the SST mediated response drives the recovery between the 1970s and 2000s. While the responses between the AGCMs used differ, there is qualitative agreement on the relative roles of the atmosphere and ocean in the overall coupled response.