Regime shifts in the Sahara and Sahel: Interactions between ecological and climatic systems in northern Africa

The Sahara and Sahel regions of northern Africa have complex environmental histories punctuated by sudden and dramatic regime shifts in climate and ecological conditions. Here we review the cur-rent understanding of the causes and consequences of two environmental regime shifts in the Sahara and Sahel. The first regime shift is the sudden tran-sition from vegetated to desert conditions in the Sahara about 5500 years ago. Geologic data show that wet environmental conditions in this region— giving rise to extensive vegetation, lakes, and wet-lands—came to an abrupt end about 5500 years ago. Explanations for climatic changes in northern Africa during the Holocene have suggested that mil