Why would there be desert in North Africa?
This rapid transition 5,500 years ago from a warm humid and wet environment to what we have today stems from a cooling of northern high latitudes. The cooler temperatures in the north weakened the high altitude Tropical Easterly Jet, which consistently brought moisture into northern Africa. Due to the weakening of the Tropical Easterly Jet, the African Easterly Jet strengthened, which indirectly inhibits rainfall in northern Africa. What is interesting is that the cooling in the northern latitudes was not all that significant compared to glacial/interglacial cycles that Earth has experienced for hundreds of thousands of years. This means slight variations in average temperature of the northern high latitudes could have a "light switch" effect turning on and off precipitation in northern Africa. Considering the recent warming of the planet, nowhere more so than high latitudes, it will be interesting to see if northern Africa at some point flips to a more tropical and humid environment. While historical data suggests this is likely if warming continues, the process could take hundreds of years and it's unclear how fast that tipping point is.
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