Editing Desertification (section)

=== Natural variations ===
Scientists agree that the existence of a desert in the place where the Sahara desert is now located is due to natural variations in [[Solar irradiance|solar insolation]] due to [[Axial precession|orbital precession]] of the Earth.<ref>{{Cite journal |last1=Tierney |first1=Jessica E. |last2=Pausata |first2=Francesco S. R. |last3=deMenocal |first3=Peter B. |date=2017-01-06 |title=Rainfall regimes of the Green Sahara |journal=Science Advances |language=en |volume=3 |issue=1 |pages=e1601503 |bibcode=2017SciA....3E1503T |doi=10.1126/sciadv.1601503 |issn=2375-2548 |pmc=5242556 |pmid=28116352}}</ref> Such variations influence the strength of the West African Monsoon, inducing feedback in vegetation and dust emission that amplify the cycle of wet and dry Sahara climate.<ref>{{Cite journal |last1=Pausata |first1=Francesco S. R. |last2=Messori |first2=Gabriele |last3=Zhang |first3=Qiong |date=2016-01-15 |title=Impacts of dust reduction on the northward expansion of the African monsoon during the Green Sahara period |journal=Earth and Planetary Science Letters |language=en |volume=434 |pages=298–307 |bibcode=2016E&PSL.434..298P |doi=10.1016/j.epsl.2015.11.049 |issn=0012-821X |doi-access=free}}</ref> There is also a suggestion the transition of the Sahara from savanna to desert during the mid-[[Holocene]] was partially due to overgrazing by the cattle of the local population.<ref name="Humans as Agents in the Termination of the African Humid Period">{{cite journal |last1=K. Wright |first1=David |last2=Rull |first2=Valenti |last3=Roberts |first3=Richard |last4=Marchant |first4=Rob |last5=Gil-Romera |first5=Graciela |date=26 January 2017 |title=Humans as Agents in the Termination of the African Humid Period |journal=Frontiers in Earth Science |volume=5 |pages=4 |bibcode=2017FrEaS...5....4W |doi=10.3389/feart.2017.00004 |doi-access=free}}</ref>