Robust Sahel drying in response to late 20th century forcings

The African Sahel experienced severe drying between the 1950s and the 1980s, with partial recovery since. We compare Sahel rainfall in the 20th century, pre-industrial, and increased greenhouse gases (GHG) simulations produced for the Intergovernmental Panel on Climate Change (IPCC). The simulations forced by 20th century concentrations of aerosol and GHG reproduce (i) a global change in SST akin to that associated with Sahel drought and (ii) a correspondent drying of the Sahel. We conclude that late 20th century Sahel climate was significantly dryer than pre-industrial, and at least 30% of the drying was externally forced. Comparison between 20th century runs and runs forced by GHG alone reveals the key role of reflective aerosols: they force a gradient in SST that excites robust drying in the northern edge of the Atlantic Inter-Tropical Convergence Zone (ITCZ) and in the Sahel.