Warming Climate Increases Sahara’s Spread

Climate change means the Sahara’s spread is growing.  And North Africa’s pattern of atmospheric change could affect other regions.

The Sahara’s spread is now established.  Its sands are on the march.  The desert is growing, thanks to climate change.

In the last century the region of the Sahara technically defined as desert has increased by at least 10%.  And the area that becomes technically desert – with less than 100mm of rain a year – has increased in summer, the wet season, over the same period by 16%.

And if climate change is at work in northern Africa, the same may hold true for some of the world’s other deserts as well, researchers warn.

US meteorologists report in the Journal of Climate that they looked at data from the years 1920 to 2013, to explore the annual trends.

Deserts are natural geographical features with no fixed boundaries: parts of them can bloom in rainier years, and support crops and even foraging animals, only to become extreme arid zones a year or two later.

Deserts exist because of the natural circulation of the atmosphere: air rises at the equator and descends in the subtropics to flow back to the equator nearer ground level to establish a pattern of low precipitation:  weather experts call this phenomenon the Hadley circulation, after the 18th century British natural philosopher George Hadley.

“Climate change is likely to widen the Hadley circulation causing northward advance of the subtropical deserts,” said Sumant Nigam, a professor of atmospheric and oceanic science at the University of Maryland, one of the authors of the study.  “The southward creep of the Sahara however suggests that additional mechanisms are at work as well.”

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