At https://www.smithsonianmag.com/science-nature/what-really-turned-sahara-desert-green-oasis-wasteland-180962668/ … this article is about the disappearance of the green Sahara, rather abruptly, around 4500 years ago. Most scientists have linked it either to the monsoon track shifting or to small changes in the orbital motion of the earth around the sun. Archaelogist David Wright has come up with another option. It may have been humans and their goats that tipped the balance. His idea is published in Frontiers in Earth Science.
Th Sahara has long been subject to periodic bursts of humidity and aridity. These fluctuations are thought to be caused by slight wobbles in the tilt of the earth’s orbital axis. This changes the angle at which solar radiation penetrates the atmosphere. At repeated intervals in earth’s history, the story goes, energy pouring in from the sun during the West African monsoon season, more rain comes down over North Africa. These periods have become known as the African Humid periods. As a result of more rain there is more vegetation, rivers flowed that do not now flow, and lakes filled up. Lake Chad, for example, was a much larger body of water. All this is well known but the reason why this occurs is open to debate.
Between 8000 and 4500 years ago, the transition from wet and humid to bone dry happened more rapidly in some areas than could be explained by orbital precession alone. The theory has been found wanting. Having said that there was progressive movement towards desert conditions. It did not happen all at once. The period 8000 to 4500 years ago was a period where it progressively became a desert. In the Holocene, up to 8000 years ago, the Sahara was much more greener and wetter. After 8000 years ago there was a climate switch. Why? Well, there were several noticable ccolings in global climate which coincided with aridity in North Africa, the Arabian steppe zone, and elsewhere. After 4500 years ago, coinciding with another protracted cooling episode and the collapse of Early Bronze societies in the Near and Middle East, as well as Egypt, involving droughts and famines, the greenery failed to come back – apart from within the oases locations. However, according to Wright, scientists call this period ‘poor parameterisation’. There was a corresponding change in the types and variety of plants. One may note straight away that Wright seems to downplay the severity of the cooling period – when indeed there would have been changes in vegetation.
Wright also looked at sediment cores and pollen records, in his research – and proxy data in general.Were the plants being eaten by goats. Well, presumably they may have been – right down to the ground. Goats don’t eat plant roots though as they are adapted to browsing. Wright says it was as if humans and their goats, and their herds of cattle as well, were overgrazing the grassland environment. No doubt they were in an aridity event, and therefore Wright provides us with additional proof in support of the cooling period. Wright’s proposal is that pastoralists and goat herders overgrazed the savannah grassland of the Sahara, adding to the extreme environmental downturn around 4500 years ago. However, he still reckons orbital change played a role – only that humans made it worse.
Neither is he challenging the idea the humid period prior to 8000 years ago was even wetter – and lots of animals were browsing on grassland that then existed in the Sahara. Cattle were an especially important part of culture – and SIS has published material emphasizing the role of cattle in the first half of the Holocene. Cattle were not just eaten, a mobile food source, but played a role in the mythology and traditions of the herding communities. On top of that we may note that anything catastrophic is not in the mix as far as mainstream is concerned. Even though 8000 years ago coincides with the biggest cooling event of the Holocene, the 8.2 ky event. Human socieities everywhere, and not just in North Africa or Arabia, were affected [see earlier posts, yesterday]. Also, 4500 years ago coincides with the second biggest climate cooling event [2500-2200BC]. When the MB world emerged out of the wreckage of the EB, human societies across the Near and Middle East had changed in fundamental ways. Newcomers had overtaken the earlier inhabitants, or lived alongside them. The failure to accept catastrophism by the science community is basically why goat herds are taking the blame.