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Why Does The Sahara Desert Go Green Every 21,000 Years?

"The cyclic transformation of the Sahara Desert into savannah and woodland ecosystems is one of the most remarkable environmental changes on the planet," says Edward Armstrong, climate scientist.


Sahara desert

“There is widespread evidence that the Sahara was periodically vegetated in the past, with the proliferation of rivers, lakes, and water-dependent animals such as hippos, before it became what is now desert,” he adds. Edward Armstrong is a climate scientist at the University of Helsinki and University of Bristol.


The research was published in the journal Nature Communications, and chronicles the wet phases in the Sahara. This includes the latest greening, which happened as recently as 5,000 years ago.


The changes in the Sahara can be attributed to Earth’s shifting orbital conditions - especially how wobbly the Earth is on its axis. This wobble influences seasonal contrast by impacting the amount of energy the Earth receives from the Sun in different seasons, as well as the strength of phenomena like the African Monsoon.


According to the model, the North African humid periods have occurred every 21,000 years over the past 800,000 years, thanks to warmer summers in the Northern Hemisphere intensifying the strength of the West African Monsoon system and dumping more precipitation on the Sahara. This caused the growth of savannah-type vegetation across the region.

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