The Sahara is now as dry as it was about 13,000 years ago .
By around 4200 BC , however , the monsoon retreated south to approximately where it is today , leading to the gradual desertification of the Sahara .
The Sahara is now as dry as Sahara was about 13,000 years ago .
By around 4200 BC , however , the monsoon retreated south to approximately where it is today , leading to the gradual desertification of the Sahara .