Climate Change

The Sahara Desert has grown 10% bigger in the last century

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A desert road marks the border line between Libya (front) and Algeria (back) May 29, 2014. Libya's southwestern tip in the Sahara bordering Algeria and Niger has turned into an open door for illegal migrants from sub-Saharan countries heading for Europe, with the chaotic government in Tripoli appearing to have abandoned all control. The revolt that overthrew Libyan leader Muammar Gaddafi three years ago emptied Libya's arsenals, flooded the region with guns and dismantled much of the state apparatus, giving well-organised smuggler networks the run of the border. Border officials say up to 200 Africans cross the Ghat border strip every day, most headed north to the Mediterranean coast for the onward trip to Europe by boat. Picture taken May 29, 2014. REUTERS/Ahmed Jadallah  (LIBYA - Tags: SOCIETY POLITICS IMMIGRATION)ATTENTION EDITORS: PICTURE 01 OF 31 FOR PACKAGE 'MIGRANT FLIGHT THROUGH LIBYA'TO FIND ALL IMAGES SEARCH 'JADALLAH GHAT'

Natural climate variations and global warming are likely to blame. Image: REUTERS/Ahmed Jadallah

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Climate Change

The Sahara, the world’s largest desert, stretching more than 3.5 million square miles, has grown by 10 percent over the last century due to a combination of natural climate variations and global warming, according to new research published in the Journal of Climate.

Most of the expansion has happened to the south, during historically rainy summer months, with the Sahara’s borders edging closer to agricultural areas in Sudan, Chad, and Mauritania. Northward expansion of the Sahara has happened largely during the winter months, the study found.

“The annual perspective is not very informative for water resource planning, for agricultural development,” study co-author Sumant Nigam, a climate scientist at the University of Maryland, told E&E News. The most important information is what’s happening during the “agriculturally sensitive summer season,” he said.

The growth of the Sahara, particularly toward the south, has been influenced by the Atlantic Multidecadal Oscillation, a natural climate cycle that changes the Atlantic Ocean from warm to cold phases every 60 to 80 years and can impact rainfall patterns across much of Africa. But global warming may also be altering atmospheric circulation patterns, such as the Hadley cell, which moves air from the Equator to the subtropics, drying it out as it goes and creating many subtropical deserts, including the Sahara.

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The new study is one of the first to look at changes to the Sahara over the past century by examining precipitation data. This is in contrast to previous research that studied the desert’s boundaries over shorter, decades-long periods, relying on satellite images and vegetation patterns.

“Surely there is an important anthropogenic influence there, but it is also being met with natural cycles of climate variability that add and subtract in different periods,” Nigam said. “Understanding both is important for both attribution and prediction.”

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