Research into the historical climate of today's Sahara desert shows that it dried up in just 100 or 200 years.

This rapid change, about 5000 years ago, was caused by a much slower change in the Earth's orbital parameters. The crucial point is that a slow increase in heat coming in can make a rapid change in climate.

We're now causing a much faster change in heat coming in (or, more precisely, a faster reduction in how much heat can escape into space each night). Maybe regions will become deserts in 10 years.