When you look at the great expanse of the Sahara desert today, it looks like it has been standing strong for an eternity. But for a brief period around 10,000 years ago, it was a rich, verdant land covered in lakes. A new piece of research says that humans could have been instrumental in this sharp transition from luscious green to sandy desert.
A new paper by archaeologists and ecologists from Seoul National University, South Korea, and published in the journal Frontiers in Earth Science, has investigated the role of human activity within the desertification of the Sahara. It began when African neolithic communities experimented with pastoral agriculture near the Nile river around 8,000 years ago, a technique that gradually began to creep westwards. As the communities spread, they introduced more and more livestock and an increasing amount of vegetation was removed to graze and house them.
This vegetation-chopping reduced the ground to scrub with no cover from the Sun's rays, thus increasing the amount of sunlight reflected back off the Earth's surface rather than absorbed – called its albedo – which in turn influenced atmospheric conditions. This sparked a reduction in monsoon rainfall that led to further desertification and vegetation loss. This vicious circle then eventually spread and transformed an area almost as big as the United States into a hot desert.
The study's findings challenge the bulk of previous research that suggests this transition was caused either by changes in Earth's orbit or natural changes in vegetation. The activity of Neolithic humans, however, has been known drive ecological change in parts of Europe, East Asia, and the Americas. For example, some speculate that Madagascar was shaped by humans through extensive man-made forest fires around 1,000 years ago. It isn't too much of a stretch to say the same could have happened to the Sahara.
Further work needs to be done to prove this concretely, however. The researchers hope to return to the Sahara to build on this idea by looking at what lies beneath the sand.
“There were lakes everywhere in the Sahara at this time, and they will have the records of the changing vegetation, " project leader Dr David Wright said in a statement. "We need to drill down into these former lake beds to get the vegetation records, look at the archaeology, and see what people were doing there. It is very difficult to model the effect of vegetation on climate systems. It is our job as archaeologists and ecologists to go out and get the data, to help to make more sophisticated models."
