Wet Green Sahara

19 Jan 2017

The early to mid Holocene is renowned for the Greening of the Sahara and this implies much higher levels of rainfall than in the modern world - although other causes might be hiding in the closet. The Sahara is a largely stony desert and is dry as a result of little rainfall. Between 11,000 and 5000 years ago it was covered in savannah and pockets of woodland, with lakes and rivers and streams. It was ten times wetter than it is in the modern world. This doesn't tell us a lot as it is bone dry and covered in a system of dry wadis. The first half of the period the Sahara was occupied by hunter gatherers but after 8000 years ago it was colonised by cattle herding tribes. See https://phys.org/print403956003.html

The point of the research, or the money funnel for the funds to support the research, is climate change related. The idea is to look at levels of rainfall in the past and try and project them into the future. The problem here is that it is assumed the higher rainfall pattern was related to the Milankovitch model of the orbit of the earth around the sun - but the researchers have turned up a glitch (as we shall see). The paper is in the January 18th issue of Science Advances and collates rainfall from 25000 years ago (deep into the Late Glacial Maximum) which would be useful to read just for that information. The glitch in the consensus occurs at 8000 years ago (which is our old 6200BC event). This, they found, coincided with a lengthy dry period (in northern Europe it coincided with a distinctly cool period, if not outright cold). In fact, i might well be described as a sort of mini Dryas episode (the origins of which are open to conjecture). We may note it also coincides with dramatic sea level changes. This was one feature of a BBC TV programme last week on the Orkneys. Previously they had thought the flooding of the bay off the Ness of Brodgar had occurred around the time the site was abandoned, late in the 3rd millennium BC. Neil Oliver read out the results of C14 dates obtained under the submerged bay and it seems it was flooded as far back as 8000 years ago. This is at exactly the same point in time that the North Sea basin was flooded and the Solent in the south of England was also flooded (a dry valley previously). It seems that sea levels around all the coasts of the British Isles were adjusted at this time for some obscure reason - or for a reason that it is not advisable to mention in mainstream circles. The most obvious explanation is a readjustment of the earth's geoid - geologically out of bounds. It is nice to know that North Africa was also affected - by a lengthy dry period. What is also clear is that when the wet weather returns it is not nearly as wet as it had been prior to 8000 years ago. This is reflected in the fact that savannah dominated - and cattle herding cultures. 

We are also told the researchers were interestd in how the Green Sahara interacted with the atmosphere, 'because most of the current climate models do not simulate the Green Sahara period well' - but they wouldn't would they? Climate models do not factor in catastrophism (sudden and unexpected events). It would be amazing if the models did so. One sees this lack of data whey they start talking about precession and Milankovitch - the northern hemisphere being closer to the sun (but avoiding the fact the Sahara is quite close to the equator). However, in spite of that this is a worthwhile piece of research and the climate bit might be regarded as an add-on for political reason and therefore not to be taken wholly seriously. One should be able to pluck out a few gems.

See also https://www.sciencenews.org/article/monsoon-deluges-turned-ancient-sahar... ... which tells you all you know about the mainstream explanation.