Detection and Analysis of an Amplified Warming of the Sahara Desert

Evaluation of three reanalyses (ERA-Interim, NCEP-2, and MERRA) and two observational datasets [CRU and Global Historical Climatology Network (GHCN)] for 1979-2012 demonstrates that the surface temperature of the Sahara Desert has increased at a rate that is 2-4 times greater than that of the tropical-mean temperature over the 34-yr time period. While the response to enhanced greenhouse gas forcing over most of the globe involves the full depth of the atmosphere, with increases in longwave back radiation increasing latent heat fluxes, the dryness of the Sahara surface precludes this response. Changes in the surface heat balance over the Sahara during the analysis period are primarily in the upward and downward longwave fluxes. As a result, the warming is concentrated near the surface, and a desert amplification of the warming occurs. The desert amplification is analogous to the polar amplification of the global warming signal, which is concentrated at the surface, in part, because of the vertical stability of the Arctic atmosphere. Accompanying the amplified surface warming of the Sahara is a strengthening of both the summertime heat low and the African easterly jet and a weakening of the wintertime anticyclone and the low-level Harmattan winds. Potential implications of the desert amplification include decreases in mineral dust aerosols globally, decreases in wintertime cold air surge activity, and increases in Sahel rainfall.