Sahara Desert Greening, Thanks to Global Warming

Published October 1, 2009

Dire predictions of human-induced global warming leading to expanding deserts are colliding with emerging evidence that something else is going on: North Africa’s desolate Sahara Desert is actually shrinking, with vegetation arising on land where there was nothing but sand.

Reclaiming the Desert

Satellite images of the Sahel—the vast, belt-shaped region south of the Sahara stretching from the Atlantic coast to the horn of Africa—show a steady northward march of grasses, shrubs, and even trees since the early 1980s.

While the coming and going of grasses in desert and semi-desert regions can be transient, the encroachment of sturdier vegetation, including majestic acacia trees, has caught scientists’ attention. And it’s not just the vegetation.

Stefan Kropelin, a climate scientist at the University of Cologne’s Africa Research Unit, has studied the region for more than two decades.

“Before there was not a single scorpion, not a single blade of grass,” he told the National Geographic News for a July 31 story. “Now you have people grazing their camels in areas which may not have been used for hundreds or even thousands of years. You see birds, ostriches, gazelles coming back, even sorts of amphibians coming back. The trend has continued for more than 20 years. It is indisputable.”

Climate Change Credited

Scientists agree the driving force behind the greening of the Sahara and the semi-arid Sahel is increased rainfall. Four years ago, researchers at the Royal Meteorological Institute in the Netherlands concluded the region’s increased precipitation could “strongly reduce the probability of prolonged droughts.”

The Dutch team, whose findings appeared in the journal Geophysical Research Letters, used a computer model to predict climate conditions in the Sahel. Reindert Haarsma, who led the research, told the Guardian on September 16, 2005, “We were surprised that it was such a large rainfall signal. There is a lot of uncertainty in this kind of prediction, but it is possible the Sahara region could benefit from climate change.”

Warmer, Wetter Past

Climate change is nothing new to the Sahara, an area encompassing more than 3 million square miles. The Sahara’s climate is strongly influenced by high-altitude winds that disperse monsoon rains on the desert below. Unpredictable shifts in the winds can lead to prolonged droughts or, as is apparently happening now, periods of life-sustaining rainfall.

During an extended period known as the Climate Optimum, 9,000 to 5,000 years ago, when temperatures were significantly warmer than today, both the Saharan and the Arabian deserts were wetter, supporting hunting, herding, and even some agriculture.

The Sahel has been advancing and retreating on the southern edge of the Sahara for millennia, as noted in Climate Research.

Scientists Not Surprised

“The big surprise is not that a changing climate should increase rainfall in northern reaches of the African continent, but that climate ‘experts’ should be surprised at this development,” commented geochemist Bill Balgord, Ph.D., president of Environment & Technology, Inc., a Wisconsin-based consulting firm.

“It should also come as no surprise that some of the increased precipitation might occur in portions of the semi-arid Sahel, particularly during winter, thus promoting a gradual reclamation of formerly arid lands bordering the southern Sahara,” Balgord observed.

Balgord sees higher levels of carbon dioxide playing a role in the greening of the Sahara.

“To some extent, higher ambient CO2 concentrations would also tend to accelerate plant re-colonization,” said Balgord. “Many studies have shown that elevated CO2 levels aid certain plants in resisting drought. Whenever modelers ‘discover’ counterintuitive results, it usually signals they initially lacked sufficient understanding of the most important variables that control the outcome.”

Bonner R. Cohen, Ph.D. ([email protected]) is a senior fellow at the National Center for Public Policy Research in Washington, DC.