Why And When Was The Sahara Desert Green?

Researchers unveiled that the Sahara's intermittent wet phases were orchestrated by Earth's orbital shifts, though dampened during ice ages.


A groundbreaking study illuminates North Africa’s humid epochs spanning the last 800,000 years, elucidating periodic green transitions of the Sahara Desert. Researchers unveiled that the Sahara’s intermittent wet phases were orchestrated by Earth’s orbital shifts, though dampened during ice ages.

Historical evidence suggests a periodically green Sahara, teeming with rivers, lakes, and wildlife like hippos. These lush periods potentially carved out green pathways, aiding the global migration of various species, including early humans.

Central to these green transitions is Earth’s orbital precession—a wobble in its axis—dictating seasonality every 21,000 years. This wobble modulates the Earth’s energy receipt, governing the potency of the African Monsoon and the proliferation of vegetation across the region.

However, the magnitude of these transitions has baffled most climate models—until now.


Linking Ice Ages and Desertification

Dr. Edward Armstrong, a lead researcher from both the University of Helsinki and the University of Bristol, shares, “Our revelations provide one of the first robust climate model simulations matching the known paleoclimate observations. We’ve pinpointed when and why these greening events transpired.”

By leveraging a cutting-edge climate model, the team confirmed these humid periods’ 21,000-year recurrence, steered by Earth’s orbital tweaks. This ushered in warmer Northern Hemisphere summers, amplifying the West African Monsoon and ensuing Saharan rains—hence, a flourishing desert.

Intriguingly, these humid spells took a hiatus during ice ages. Massive glacial blankets in higher latitudes cooled the globe, stifling the African monsoon’s expansion. This link between remote areas potentially hindered species migration out of Africa during ice-laden epochs.

Predicting the Future by Studying the Past

Professor Paul Valdes, co-author from the University of Bristol, conveys, “Our upgraded model not only mirrors past transitions but also bolsters our understanding of impending climate changes.”

Further underscoring the Sahara’s pivotal role, co-author Miikka Tallavaara states, “The Sahara acts as a gate, dictating species dispersion both within and beyond Africa’s boundaries.”


He adds, “The Sahara’s alternating wet-dry phases profoundly impacted species evolution in Africa. Our enhanced modeling prowess now allows a deeper dive into human evolution and distribution.”

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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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