The drought helped kick things over the threshold into open conflict. And a drought of that severity was made much more likely by the ongoing human-driven drying of that region.
In a dire chain of cause and effect, the drought that devastated parts of Syria from 2006 to 2010 was probably the result of climate change driven by human activities, a new study says.
And the study's authors think that the drought may also have contributed to the outbreak of Syria's uprising in 2011. The ensuing civil war has left at least 200,000 people dead, and has displaced millions of others.
The drought, which was the worst ever recorded in the region, ravaged agriculture in the breadbasket region of northern Syria, driving dispossessed farmers to the cities where poverty, government mismanagement and other factors created the unrest that exploded four years ago.
The authors are clear that the climatic changes were human-driven (anthropogenic) and cannot be attributed simply to natural variability - but are careful to stress that their findings are tentative.
"We're not saying the drought caused the war", says Richard Seager, one of the co-authors. "We're saying that, added to all the other stressors, it helped kick things over the threshold into open conflict. And a drought of that severity was made much more likely by the ongoing human-driven drying of that region."
Climate link to violence
Their study, although it contains new material, is not the first to suggest a possible link between extreme weather and the likelihood of violence.
Some researchers have investigated whether there may be a link between El Niño and La Niña - the periodic Pacific weather disruptions - and outbreaks of unrest. Suggestions of a global connection between climate change and political instability is being taken seriously by two influential groups - insurers and military planners.
Syria was not the only country affected by the drought. It struck the Fertile Crescent, linking Turkey, Syria and Iraq, where agriculture and animal herding are believed to have started around 12,000 years ago.
The Levant has always seen natural weather swings. Other research has suggested that the Akkadian empire, spanning much of the Fertile Crescent about 4,000 years ago, probably collapsed during a long drought.
But the authors of the Lamont-Doherty study, using existing studies and their own research, showed that the area has warmed by between 1°C and 1.2°C since 1900, and has undergone a 10% reduction in wet season precipitation. They say this trend is a neat match for models of human-influenced global warming, and so cannot be attributed to natural variability.
Global warming has had two effects, they say. First, it appears to have indirectly weakened wind patterns that bring rain-laden air from the Mediterranean, reducing precipitation during the usual November-April wet season. And higher temperatures have increased the evaporation of moisture from soils during the hot summers.
Other researchers have observed the long-term drying trend across the Mediterranean region, and have attributed at least part of it to anthropogenic warming.
Government stuck with water-intensive cash crops
The government has also encouraged water-intensive export crops such as cotton, while illegal drilling of irrigation wells depleted groundwater, says co-author Shahrzad Mohtadi, an international affairs consultant at the US Department of State.
The drought's effects were immediate and overwhelming. Agricultural production - typically, a quarter of Syria's gross domestic product - fell by a third. In the northeast, livestock was practically wiped out, cereal prices doubled, and nutrition-related diseases among children increased steeply.
And Syria was especially vulnerable because of other factors - including a huge increase in population from four million in the 1950s to 22 million in recent years. As many as 1.5 million people fled from the countryside to cities already strained by waves of refugees from the war in neighbouring Iraq.
"Rapid demographic change encourages instability", the authors say. "Whether it was a primary or substantial factor is impossible to know, but drought can lead to devastating consequences when coupled with pre-existing acute vulnerability."
Solomon Hsiang, professor of public policy at the University of California, Berkeley, says the study is "the first scientific paper to make the case that human-caused climate change is already altering the risk of large-scale social unrest and violence."
Alex Kirby writes for Climate News Network.