Generalized Walker Circulation (December-February) during ENSO-neutral conditions. Convection associated with rising branches of the Walker Circulation is found over the Maritime continent, northern South America, and eastern Africa. [Credit: NOAA Climate.gov — drawing by Fiona Martin]El Niño and 100,000 year glaciation/climate cycles feature prominently in this research. The Walker circulation has been described as ENSO’s atmospheric buddy.
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While it is widely accepted that climate change drove the evolution of our species in Africa, the exact character of that climate change and its impacts are not well understood, says Phys.org.

Glacial-interglacial cycles strongly impact patterns of climate change in many parts of the world, and were also assumed to regulate environmental changes in Africa during the critical period of human evolution over the last ~1 million years.

The ecosystem changes driven by these glacial cycles are thought to have stimulated the evolution and dispersal of early humans.

A paper published in Proceedings of the National Academy of Sciences (PNAS) this week challenges this view.

Dr. Kaboth-Bahr and an international group of multidisciplinary collaborators identified ancient El Niño-like weather patterns as the drivers of major climate changes in Africa. This allowed the group to re-evaluate the existing climatic framework of human evolution.

Walking with the rain

Dr. Kaboth-Bahr and her colleagues integrated 11 climate archives from all across Africa covering the past 620 thousand years to generate a comprehensive spatial picture of when and where wet or dry conditions prevailed over the continent.

“We were surprised to find a distinct climatic east-west ‘seesaw’ very akin to the pattern produced by the weather phenomena of El Niño, that today profoundly influences precipitation distribution in Africa,” explains Dr. Kaboth-Bahr, who led the study.

The authors infer that the effects of the tropical Pacific Ocean on the so-called “Walker Circulation”—a belt of convection cells along the equator that impact the rainfall and aridity of the tropics—were the prime driver of this climate seesaw.

The data clearly shows that the wet and dry regions shifted between the east and west of the African continent on timescales of approximately 100,000 years, with each of the climatic shifts being accompanied by major turnovers in flora and mammal fauna.

“This alternation between dry and wet periods appeared to have governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa,” explains Dr. Kaboth-Bahr. “The resultant environmental patchwork was likely to have been a critical component of human evolution and early demography as well.”

The scientists are keen to point that although climate change was certainly not the sole factor driving early human evolution, the new study nevertheless provides a novel perspective on the tight link between environmental fluctuations and the origin of our early ancestors.

Full article here.

via Tallbloke’s Talkshop

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June 1, 2021