The desertification of the Sahara — the largest hot desert and the third largest desert in the world — has long been a target for researchers trying to understand climate and ecological tipping points. A new paper by Seoul National University geoarchaeologist David Wright challenges the conclusions of most studies done to date that point to changes in the Earth’s orbit or natural changes in vegetation as the major driving forces.

“In East Asia there are long established theories of how Neolithic populations changed the landscape so profoundly that monsoons stopped penetrating so far inland,” said Dr. Wright, an assistant professor in the Department of Archaeology and Art History at Seoul National University, Seoul, South Korea.

“Evidence of human-driven ecological and climatic change has been documented in Europe, North America and New Zealand. Similar scenarios could also apply to the Sahara.”

To test his hypothesis, Dr. Wright reviewed archaeological evidence documenting the first appearances of pastoralism — the use of extensive grazing on rangelands for livestock production — across the Saharan region.

He then compared this with records showing the spread of scrub vegetation, an indicator of an ecological shift towards desert-like conditions.

The findings confirmed his thoughts: beginning approximately 8,000 years ago in the regions surrounding the Nile River, pastoral communities began to appear and spread westward, in each case at the same time as an increase in scrub vegetation.

Growing agricultural addiction had a severe effect on the region’s ecology.

As more vegetation was removed by the introduction of livestock, it increased the albedo — the amount of sunlight that reflects off the Earth’s surface — of the land, which in turn influenced atmospheric conditions sufficiently to reduce monsoon rainfall.

The weakening monsoons caused further desertification and vegetation loss, promoting a feedback loop which eventually spread over the entirety of the modern Sahara.

“There were lakes everywhere in the Sahara at this time, and they will have the records of the changing vegetation,” Dr. Wright said.

“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,” he said.

The paper was published online Jan. 26, 2017 in the journal Frontiers in Earth Science.

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David K. Wright. Humans as Agents in the Termination of the African Humid Period. Front. Earth Sci., published online January 26, 2017; doi: 10.3389/feart.2017.00004