@kevinrns Your interesting choice of words (Sahara-fication rather than Desertification) prompted me to do some research...

What Really Turned the #SaharaDesert From a Green Oasis Into a Wasteland?

10,000 years ago, this iconic desert was unrecognizable. A new hypothesis suggests that humans may have tipped the balance

by Lorraine Boissoneault
March 24, 2017

Excerpt: "'By overgrazing the grasses, they were reducing the amount of atmospheric moisture—plants give off moisture, which produces clouds—and enhancing albedo,' Wright said. He suggests this may have triggered the end of the humid period more abruptly than can be explained by the orbital changes. These nomadic humans also may have used fire as a land management tool, which would have exacerbated the speed at which the desert took hold.

"It’s important to note that the green Sahara always would’ve turned back into a desert even without humans doing anything—that’s just how Earth’s orbit works, says geologist Jessica Tierney, an associate professor of geoscience at the University of Arizona. Moreover, according to Tierney, we don’t necessarily need humans to explain the abruptness of the transition from green to desert.

"Instead, the culprits might be regular old vegetation feedbacks and changes in the amount of dust. 'At first you have this slow change in the Earth’s orbit,' Tierney explains. 'As that’s happening, the West African monsoon is going to get a little bit weaker. Slowly you’ll degrade the landscape, switching from desert to vegetation. And then at some point you pass the tipping point where change accelerates.'

"Tierney adds that it’s hard to know what triggered the cascade in the system, because everything is so closely intertwined. During the last humid period, the Sahara was filled with hunter-gatherers. As the orbit slowly changed and less rain fell, humans would have needed to domesticate animals, like cattle and goats, for sustenance. 'It could be the #climate was pushing people to herd cattle, or the #overgrazing practices accelerated denudation [of foliage],' Tierney says.

"Which came first? It’s hard to say with evidence we have now. “The question is: How do we test this hypothesis?” she says. 'How do we isolate the climatically driven changes from the role of humans? It’s a bit of a chicken and an egg problem.' Wright, too, cautions that right now we have evidence only for correlation, not causation.

"But Tierney is also intrigued by Wright’s research, and agrees with him that much more research needs to be done to answer these questions."

Full article:
https://www.smithsonianmag.com/science-nature/what-really-turned-sahara-desert-green-oasis-wasteland-180962668/