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Global warming, drought, and war

A new study that focuses on events in Syria contends there is a connection.

WASHINGTON - The conflict that has torn Syria apart can be traced, in part, to a record drought worsened by global warming, a new study says.

In what scientists say is one of the most detailed and strongest connections between violence and human-caused climate change, researchers from Columbia University and the University of California Santa Barbara trace the effects of Syria's drought from the collapse of farming, to the migration of 1.5 million farmers to the cities, and then to poverty and civil unrest. Syria's drought started in 2007 and continued until at least 2010 - and perhaps longer. Weather records are more difficult to get in wartime.

"There are various things going on, but you're talking about 1.5 million people migrating from the rural north to the cities," said climate scientist Richard Seager at Columbia, a coauthor of the study published Monday in the journal Proceedings of the National Academy of Sciences. "It was a contributing factor to the social unraveling that occurred that eventually led to the civil war."

The study's authors do not claim climate change caused Syria's civil war. Lead author Colin Kelley at the University of California said there are numerous factors involved, including the oppressive regime, an influx of more than a million refugees from Iraq, the tumult of the Arab Spring, as well as the drought. Kelley and Seager said they couldn't say which factors were the most important.

But, Seager said, this is the "single clearest case" ever presented by scientists of climate change playing a part in conflict because "you can really draw a blow-by-blow account with the numbers."

Kelley and Seager do statistical and computer simulation analysis to connect global warming to the multiyear drought, finding that such dry spells are two to three times more likely because of human-caused heat-trapping carbon dioxide in the atmosphere than under natural conditions. The connection between climate change and drought in the eastern Mediterranean is one of the most robust in science, said Seager and other scientists.

They also show that Syria's temperature has risen nearly 2 degrees Fahrenheit since 1900, which adds to drying through evaporation, and winter rainfall has dropped.

In a separate study, published in the same journal, Stanford University climate scientist Noah Diffenbaugh said the long-time upward trend in California's temperatures have caused the drought there to be worse, regardless of the initial cause of lack of rain. Diffenbaugh didn't see much of a change in rainfall, but a big one in terms of warming.