"Absurd," "embarrassing," and "brazenly silly" were some of the insults hurled at Democratic presidential candidate Martin O’Malley when he suggested in July that climate change contributed to the rise of ISIS. Despite the derision, the former governor of Maryland continues to stand by his talking point.

"One of the things that preceded the failure of the nation-state of Syria and the rise of ISIS was the effect of climate change and the mega-drought that affected that region, wiped out farmers, drove people to cities, created a humanitarian crisis," O’Malley told Bloomberg TV on July 20.

Two months later, O’Malley repeated his argument in an interview with the progressive radio show Democracy Now! on Sept. 10: "Their government could not take care of the basic needs of families in those conditions. Civil war rose up as a result of protest and repression ... then the vacuum to that led to ISIS. So these are the cascading effects that happen in a world that’s very, very connected and in a world where climate change is now creating extreme weather conditions, prolonged droughts."

With recent events -- the pope’s visit highlighting climate change and the United States’ decision to accept more Syrian refugees -- converging on the topic, we were curious if O’Malley’s claim really was "absurd."

O’Malley’s source

A spokesperson for the O’Malley campaign told us that his source was a March 2015 study published in the Proceedings of the National Academy of Sciences. The study, which was well received in its field, does not mention ISIS at all, but its authors told us O’Malley’s extrapolation makes sense.

The study found evidence that climate change led to an extreme drought in Syria’s breadbasket between 2006 to 2009. Food prices skyrocketed, nutrition-related diseases became widespread, and 1.5 million internal refugees abandoned their farms and flooded into Syrian cities already crowded with 1.5 million Iraqi refugees displaced by the Iraq war, according to the study.

This influx of people exacerbated existing problems like unemployment, corruption and brewing discontent with the regime of Bashar al-Assad, which failed to respond to the situation, according to the study. In 2011, the unrest reached boiling point and erupted into the Syrian uprising.

If we follow the sequence of events like O’Malley does, it’s reasonable to say the next fallen domino is the rise of ISIS.

"Once the war had begun all sorts of pre-existing actors took advantage of the situation to pursue their goals -- ISIS was one and the collapse of Syria provided fertile ground for their actions," said co-author Richard Seager, a professor of climatology at Columbia University.

O’Malley’s campaign also forwarded us many reports and comments from the Department of Defense linking climate change and ISIS. We should also note that the Proceedings of the National Academy of Sciences study is not the first rigorous, academic investigation into the links between climate change and conflict (there’s at least one other on the Syrian conflict alone).

Drought’s not the sole culprit

In the grander scheme of things, experts say, the drought was just one of many sparks that set the Syrian powder keg ablaze. But both the study and O’Malley acknowledge that and get credit for not overstating climate change’s impact.

While climate change may have played an indirect role in the Syrian uprising and ISIS’ rise, other causes – Assad’s recruitment of al-Qaeda members, the genocide against Sunni Arabs, etc.– are direct and "crystal clear," according to Ali Khedery, a former special assistant to five American ambassadors in Iraq.

Michael Doran, a senior fellow on Middle East security issues at the Hudson Institute, a conservative think tank, pointed out that unrest in region is not confined to areas suffering from drought. He, however, said that O’Malley’s correct that the drought played a role in generating disaffection.

"The drought did not cause the Syrian revolution or the fall of Assad," said Kenneth Pollack, a senior fellow on Middle East policy at the Brookings Institution. "A very complex mix of factors did that, but the study suggests that climate change was part of that mix even if we can't tell how important it was."

The study, which Pollack said is garnering a lot of attention among Middle East experts, notes that there is no single cause for conflict, while O’Malley emphasized the "cascading effects" of the drought, rather than the drought itself.

"It's fair to say the uprising was going to happen at some point. But the drought did happen when it happened and based on the timing of it, the agricultural collapse and the migration were direct results," said study lead author Colin Kelley, a climatologist at the University of California at Santa Barbara. "The drought creating this chaotic situation also created better opportunity for ISIS to thrive. If you say that in the way (O’Malley) said, it's fair to argue."

Our ruling

O’Malley argued that "the cascading effects" of climate change contributed to the rise of ISIS

The O’Malley campaign referred us to a credible March 2015 study that supports his point. According to the study, a drought in Syria in the 2000s displaced millions of refugees and added to discontent that eventually erupted into war. While the study does not mention ISIS by name, the authors say O’Malley is simply taking their argument one step further.

Experts agreed that the drought, spurred by climate change, was one of many factors that led to the Syrian conflict. O’Malley’s phrasing suggests he understands this and is careful not overstate it.

We rate his claim Mostly True.