Not always Sahara it was a desert. A group of scientists discovered that this region over time Periodic phases of ‘greening’ and increasing moisture repeated every 21,000 years and these are a result of the Earth’s orbit. In this way, the Sahara became cyclically forest, savannah and desert.
Published in research Nature Communicationmoist and green phases that occur periodically in the Sahara It is caused by changes in the Earth’s orbit around the Sun On the other hand, they were suppressed during the ice ages.
For the first time, climate scientists have simulated the Sahara’s historic “greening” intervals, obtaining evidence of the duration and intensity of these rainy events. They were also affected by the effects of glacial periods in the Northern Hemisphere..
Lead author Edward Armstrong, a climate scientist at the University of Helsinki and the University of Bristol, said: “The cyclical transformation of the Sahara Desert into savannah and forest ecosystems This is one of the most remarkable environmental changes on the planet.”.
“Our study is one of the first climate modeling studies to simulate African wet periods at a magnitude comparable to those shown by paleoclimatic observations and reveal why and when these events occur,” he added.
A Sahara with its rivers and lakes
There is widespread evidence that The Sahara was periodically covered with vegetation in the past due to the proliferation of rivers, lakes, and water-dependent animals.like hippos, before turning into what is now a desert.
These wet periods in North Africa may have been crucial in providing vegetated corridors to other continents and allowing many species, including early humans, to spread around the world.
along the Earth’s orbit
‘Greenings’ are believed to be caused by changes in Earth’s orbital conditions, specifically Earth’s orbital precession. Precession is a movement in which the Earth oscillates around its axis, affecting the seasons. over a cycle of approximately 21,000 years. These changes in motion determine the amount of energy the Earth receives in different seasons, which in turn Controls the strength of the African monsoon and the expansion of vegetation in this vast region.
A major obstacle to understanding these events is that most climate models cannot simulate the extent of these wet spells, so the specific mechanisms driving them remain unclear.
However, a recently developed climate model was used in this study. To simulate the rainy periods of North Africa and thus better understand the mechanisms that trigger them.
The results confirm that North Africa’s wet spells occur every 21,000 years due to changes in the Earth’s orbital motion. This caused summers to be hotter in the northern hemisphere. Intensified the strength of the West African monsoon system and increased Saharan rainfallcaused the spread of savannah-type vegetation throughout the desert.
Disruption during ice ages
The findings also show that: These wet periods did not occur during ice agesTimes when large glacial ice sheets covered most of the high latitudes. This is because these extensive ice sheets cool the atmosphere and suppress the widening tendency of the African monsoon system.
This highlights an important issue connection between these remote areasThis may have restricted the spread of species, including humans, out of Africa during glacial periods of the last 800,000 years.
Co-author Paul Valdés, Professor of Physical Geography at the University of Bristol, said: “We are very excited about the results. Traditionally climate models have struggled to represent the extent of the ‘greening’ of the Sahara. Our revised model successfully represents past changes and also gives us confidence in your ability to understand future changes”.
Co-author Miikka Tallavaara, assistant professor of hominid environments at the University of Helsinki, said: “The Saharan region is a kind of gateway that controls the distribution of species between northern and sub-Saharan Africa and within and outside the continent.” .
“The door was open when the Sahara was green, closed when the deserts dominated. This alternation of wet and dry phases had important consequences. Spread and evolution of species in Africa. “Our ability to model wet periods in North Africa is a significant achievement and means we can now better model human distributions and better understand the evolution of our species in Africa.”
Reference work: https://www.nature.com/articles/s41467-023-41219-4
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