NYTimes:

The researchers said this trend matched computer simulations of how the region responds to increases in greenhouse-gas emissions, and appeared to be due to two factors: a weakening of winds that bring moisture-laden air from the Mediterranean and hotter temperatures that cause more evaporation.

Colin P. Kelley, the lead author of the study, said he and his colleagues found that while Syria and the rest of the region known as the Fertile Crescent were normally subject to periodic dry periods, “a drought this severe was two to three times more likely” because of the increasing aridity in the region.

Dr. Kelley, who did the research while at Lamont-Doherty Earth Observatory and is now at the University of California at Santa Barbara, said there was no apparent natural cause for the warming and drying trend, which developed over the last 100 years, when humans’ effect on climate has been greatest.

Martin P. Hoerling, a meteorologist at the National Oceanic and Atmospheric Administration whose earlier work showed a link between climate change and aridity in the Eastern Mediterranean, said the researchers’ study was “quite compelling.”

“The paper makes a strong case for the first link in their causal chain,” Dr. Hoerling said in an email, “namely the human interference with the climate so as to increase drought likelihood in Syria.”