The main thing that interested me about this article is its explanation for the Sahara's cycling between dry and humid periods. It's basically due to increased solar radiation falling upon the Northern Hemisphere during summertime.
quote:The Sahara's green shift happened because Earth's tilt changed. About 8,000 years ago, the tilt began moving from about 24.1 degrees to the current day 23.5 degrees, Space.com, a Live Science sister site, previously reported. That tilt variation made a big difference; right now, the Northern Hemisphere is closest to the sun during the winter months. (This may sound counterintuitive, but because of the current tilt, the Northern Hemisphere is tilted away from the sun during the winter season.) During the Green Sahara, however, the Northern Hemisphere was closest to the sun during the summer.
This led to an increase in solar radiation (in other words, heat) in Earth's Northern Hemisphere during the summer months. The rise in solar radiation amplified the African monsoon, a seasonal wind shift over the region caused by temperature differences between the land and ocean. The increased heat over the Sahara created a low pressure system that ushered moisture from the Atlantic Ocean into the barren desert. (Usually, the wind blows from dry land toward the Atlantic, spreading dust that fertilizes the Amazon rainforest and builds beaches in the Caribbean, Live Science previously reported.)
This increased moisture transformed the formerly sandy Sahara into a grass and shrub-covered steppe, according to the National Oceanic and Atmospheric Administration (NOAA). As animals there prospered, humans did too, eventually domesticating buffalo and goats and even creating an early system of symbolic art in the region, NOAA reported.
Posted by Tukuler (Member # 19944) on :
Good gosh
Eurocentricity now claims the African Humid Period due to West African Monsoon northward movement driven by a ~20,000 year celestial tilt cycle is Europe-proxy determined?
What these ppl won't stop at in their drive for superiority! Or to claim Sahra Sun power is thus rightfully America's, Europe's and even China's?
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SAHARA TIMELINE • 40m sea bed (once a part of Tethys) • 3m tropical swamp dries as desert is born • 90k monsoon greens the region
Due to the cosmos, at least from 90k on, every 20000 years the Monsoon extends north for 5000 years. Then it swiftly retreats back south within 200 years leaving a desert for the next 15000 years.
That's the cycle. The Green Sahra event is birthed by West African Monsoon moisture when at its northmost position per Earth's wobble.
Anyway, if Nature unimpeded by man&woman has Her way, Sahra will green again and again. But as we're seeing, the effects of our new 'Homocene' era is recalling cards and reshuffling the deck. All we can really say is "Que sera sera Jim", huh? I mean man&woman's 'mission' is subdue and harness nature, right
Sahra-centric moisture timeline with relevant events and locales --please critique--
Posted by BrandonP (Member # 3735) on :
quote:Originally posted by Tukuler: Good gosh
Eurocentricity now claims the African Humid Period due to West African Monsoon northward movement driven by a ~20,000 year celestial tilt cycle is Europe-proxy determined?
What these ppl won't stop at in their drive for superiority! Or to claim Sahra Sun power is thus rightfully America's, Europe's and even China's?
Uh...what is Eurocentric about the article? If it's the part where it mentions the Northern Hemisphere, that's simply all of Earth north of the Equator. Half of Africa is in the Northern Hemisphere.
Posted by Tukuler (Member # 19944) on :
Solid.
How do you suggest I alter that post since you can't see China, America, and Europe are all completely within the northern hemisphere.
Me? I'm cock sure by northern hemisphere the authors and many readers envision only the Glacial Maximum effected regions. There I go projecting (well at least I caught myself).
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But HEY whaddabout a chart critique, Bosz ?
Posted by Djehuti (Member # 6698) on :
The climatological evidence presented here alone makes one wonder about all the man-made climate change scare going on. As far as geologists know, the Earth had 5 major Ice Ages or Maximum Glaciation Periods followed by warming periods much less many more smaller Ice Ages. As someone who took environmental sciences back in my undergrad I know there are many factors that go into climate change besides man-made carbon emmisions.
But getting back to the topic, it wasnt' just the Sahara but Arabia also that was once green.
Even many of the the flora and fauna was shared between Africa and Southwest Asia which is why bio-geographers refer to an Afro-Arabian or Afro-Asiatic range.
Posted by Tukuler (Member # 19944) on :
Well yes, as GK Osei and others taught decades ago and Spencer Wells wrote in his Journey of Man, the entire Arabian Peninsula up to the Rock is natural Africa.
Anc Greek worship and European politics keep it out of Africa despite geology, climate, terrain, etc., evince.
quote:Modern humans had been present in the Levant (the east region of the Mediterranean) since at least 111,100 years ago, but the population was never extensive and was limited to a few sites. During this early phase of the last ice age, the eastern Mediterranean was effectively an extension of northern Africa with similar climatic conditions and animals.
I bumped the Fertile Landscapes thread where you can track the Arabian Plate along with continental Africa from just before the Holocene to ~3000 BCE.
Posted by Archeopteryx (Member # 23193) on :
With he help of new simulation methods researchers have been able to get a more detailed picture of the causes behind, and timing of the Green Sahara periods:
quote: A pioneering study has shed new light on North African humid periods that have occurred over the past 800,000 years and explains why the Sahara Desert was periodically green.
The research, published in Nature Communications, showed periodic wet phases in the Sahara were driven by changes in Earth’s orbit around the Sun and were suppressed during the ice ages.
For the first time, climate scientists simulated the historic intervals of ‘greening’ of the Sahara, offering evidence for how the timing and intensity of these humid events were also influenced remotely by the effects of large, distant, high-latitude ice sheets in the Northern Hemisphere.
Lead author Dr Edward Armstrong, a climate scientist at the University of Helsinki and University of Bristol, said: “The cyclic transformation of the Sahara Desert into savannah and woodland ecosystems is one of the most remarkable environmental changes on the planet.
“Our study is one of the first climate modelling studies to simulate the African Humid Periods with comparable magnitude to what the palaeoclimate observations indicate, revealing why and when these events occurred.”
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. These North African Humid Periods may have been crucial in providing vegetated corridors out of Africa, allowing the dispersal of various species, including early humans, around the world.
The Sahara region has experienced periodic wet periods over the Quaternary and beyond. These North African Humid Periods (NAHPs) are astronomically paced by precession which controls the intensity of the African monsoon system. However, most climate models cannot reconcile the magnitude of these events and so the driving mechanisms remain poorly constrained. Here, we utilise a recently developed version of the HadCM3B coupled climate model that simulates 20 NAHPs over the past 800 kyr which have good agreement with NAHPs identified in proxy data. Our results show that precession determines NAHP pacing, but we identify that their amplitude is strongly linked to eccentricity via its control over ice sheet extent. During glacial periods, enhanced ice-albedo driven cooling suppresses NAHP amplitude at precession minima, when humid conditions would otherwise be expected. This highlights the importance of both precession and eccentricity, and the role of high latitude processes in determining the timing and amplitude of the NAHPs. This may have implications for the out of Africa dispersal of plants and animals throughout the Quaternary.
Edward Armstrong, Miikka Tallavaara, Peter O. Hopcroft, Paul J. Valdes. North African humid periods over the past 800,000 years. Nature Communications, 2023; 14
