Explaining the Drought

Utilizing state-of-the-art computer models of global climate, simulations were generated from 50 years of observed monthly sea surface temperature measurements. The study began with the actual recorded conditions of the atmosphere in 1950. In each subsequent simulation the starting point of the actual conditions was slightly varied in order to create a collection of equally plausible climate histories. Five different models were used and 80 simulations performed. Surprisingly all 80 simulations produced drying over the Sahel and also over southern Africa, confirming that the truly observed increased incidence of drought was fully determined by the ocean.

For the Sahel, additional focused experiments revealed that the drying was linked to a cooling of the water in the tropical region of the Atlantic just north of the equator relative to warming of the tropical South Atlantic. On the other hand, southern African drying, though also of ocean origins, was attributed to a progressive warming of the Indian Ocean.