Between 8,000 to 5,500 years ago the Earth was as warm as it is now, and the Sahara was a rainforest. Much of this was down to the Earth’s tilt, or precession, the stronger sun on the greenery driving water further inland to keep even the heart of the area moist. Over the course of a century the Sahara’s ecosystem collapsed as the precession continued and changed sunlight levels and localised browning reduced the amount of moisture to be transferred. Now the dust that used to be the bed of lake Megachad is picked up by the wind and carried across the Atlantic to fertilise the Amazon.
It’s possible that global warming could see a return of heavy rains to the Sahara and a regreening of the arid zone. However this isn’t such good news on the global scale as other areas, notably prosperous zones like the west of North America, suffer ever longer drought periods. The Amazon could collapse as the Sahara blooms.
The Independent article linked to is an edited extract from The Last Generation by Fred Pearce.