Department of Geography

Flip-flops in the desert

Why did the Sahara flip from green to brown in the mid-Holocene

Sahara maps

About 6000 years ago (during the mid ‘Holocene’ period), today’s Saharan desert was green, a phenomenon known as the African Humid Period. Evidence of this comes from both ancient rock paintings (see below) and from palaeo environmental indicators. However, ocean sediment cores indicate that the African Humid Period terminated rather suddenly around 5500 years ago. The reasons for this abrupt and dramatic climate shift remain to be resolved. Our research investigated the potential processes causing this abrupt change using an advanced climate model. We found that complex self-reinforcing interactions among vegetation, soil moisture, evapotranspiration and local rainfall can combine to produce dramatic changes in rainfall over the Sahara. This illustrates the complex feedback process interactions within the Earth system.

Find out more...