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https://theconversation.com/the-sahara-desert-used-to-be-a-green-savannah-new-research-explains-why-216555>
"Algeria’s Tassili N’Ajjer plateau is Africa’s largest national park. Among its
vast sandstone formations is perhaps the world’s largest art museum. Over
15,000 etchings and paintings are exhibited there, some as much as 11,000 years
old according to scientific dating techniques, representing a unique
ethnological and climatological record of the region.
Curiously, however, these images do not depict the arid, barren landscape that
is present in the Tassili N'Ajjer today. Instead, they portray a vibrant
savannah inhabited by elephants, giraffes, rhinos and hippos. This rock art is
an important record of the past environmental conditions that prevailed in the
Sahara, the world’s largest hot desert.
These images depict a period approximately 6,000-11,000 years ago called the
Green Sahara or North African Humid Period. There is widespread climatological
evidence that during this period the Sahara supported wooded savannah
ecosystems and numerous rivers and lakes in what are now Libya, Niger, Chad and
Mali.
This greening of the Sahara didn’t happen once. Using marine and lake
sediments, scientists have identified over 230 of these greenings occurring
about every 21,000 years over the past eight million years. These greening
events provided vegetated corridors which influenced species’ distribution and
evolution, including the out-of-Africa migrations of ancient humans.
These dramatic greenings would have required a large-scale reorganisation of
the atmospheric system to bring rains to this hyper arid region. But most
climate models haven’t been able to simulate how dramatic these events were.
As a team of climate modellers and anthropologists, we have overcome this
obstacle. We developed a climate model that more accurately simulates
atmospheric circulation over the Sahara and the impacts of vegetation on
rainfall.
We identified why north Africa greened approximately every 21,000 years over
the past eight million years. It was caused by changes in the Earth’s orbital
precession - the slight wobbling of the planet while rotating. This moves the
Northern Hemisphere closer to the sun during the summer months."
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
