Human habitation in North Africa has been greatly influenced by the climate of the Sahara (currently the world's largest warm desert), which has undergone enormous variations between wet and dry over the last few hundred thousand years. This is due to a 41000-year Axial tilt cycle in which the tilt of the earth changes between 22° and 24.5°. At present (2000 AD), we are in a dry period, but it is expected that the Sahara will become green again in 15000 years (17000 AD).