Robust response of Sahel precipitation to late 20th century forcings: natural or anthropogenic?

Using the multi-model dataset produced for the fourth assessment report of the Intergovernmental Panel on Climate Change, we compare Sahel rainfall in the 20th century, pre-industrial, and increased greenhouse gases simulation. We show a strong agreement across models that anthropogenic emissions between pre-industrial and present times have forced (i) a global change in SST in the same pattern as the one associated in observations with the Sahel drought and (ii) the correspondent decline in Sahelian rainfall. We also present an argument that the aerosol forcing is a dominant player in the simulation of robust anomalies in the region. Northern Hemisphere sulfate aerosols induce a negative SST gradient in the tropical Atlantic, reduced monsoon flow and reduced moisture advection into the Sahel. This, coupled to a moisture "upped-ante" for convection in a warmer climate, induces drought in the Sahel.