It was only 6,000 years ago that it frequently rained in the Sahara desert, leaving it covered in vast vegetation and grasslands, so what happened?
The transformation of a heavily vegetated region into one of the most arid plains on earth does not happen overnight, and Professors Robert Korty and William Boos have been trying to track down the origin of this change.
The team began by comparing the Holocene era, which began 12,000 to 11,500 years ago at the close of the Paleolithic ice age as earth entered a warming period, to the present-day intertropical convergence zone and Hadley circulation.
The Hadley circulation rises near the equator and where it descends in the subtropics, it can create desert-like conditions. In fact, most of Earth’s driest regions are in areas beneath the Hadley circulation.
Building a framework, Korty and Boos concluded that the tropical belts of rain that used to hover over the Sahara, have now migrated north away from the equator. But, crucially, this doesn’t necessitate that all other bands of wet weather in the Hadley circulation also have to move elsewhere too.
Instead, they respond to individual forces, explaining why the Sahara seems unique in its change.
“Tropical rain belts are tied to what happens elsewhere in the world through the Hadley circulation, but it won’t predict changes elsewhere directly, as the chain of events is very complex. But it is a step toward that goal.”
“The framework we developed helps us understand why the heaviest tropical rain belts set up where they do,” Korty explains.