Scholars studying drought and global warming in the Middle East are reviewing evidence linking the uprising against the Assad Regime that started during the “Arab Spring” of 2011, to the drought of 2007-2010. Those conclusions emerged from a new study by the University of California, Santa Barbara that found a very clear signal of climate change over the Eastern Mediterranean and the Fertile Crescent.

Winter brings rain to Syria’s Mediterranean climate and the winter of 2008-09 was the driest winter on record in the previous 100 years, causing severe damage to the domestic wheat crop. Despite its semi-arid climate, Syria normally has enough rain to support substantial agriculture, albeit limited to areas in the North and near the Mediterranean coast. Drought has wreaked havoc on croplands with tight water resources between 2007 and 2010. Crop failures caused by three parched years in a row forced about 1.5 million farmers to move into the cities.

There they were joined by almost as many more refugees from the Iraq war. Between 2002 and 2010, Syria’s urban population rose by 50 percent. The Syrian government did little or nothing to ease the suffering of the displaced population. The resulting discontent then became instrumental in the opposition to President Bashar al-Assad.

Droughts have forced migrations in the past, but this time the sheer size of the population made a difference. The population in most of Syria, 40 or 50 years ago, was a small fraction of what it is today, and the increased population makes a stronger demand for water.

We can’t be sure that climate change, acting through drought, caused the Syrian uprising. It’s impossible to know what would have happened in the absence of severe drought and without this huge influx of agricultural refugees. You could make the argument that it would have happened anyway. Syria was the last of the Arab spring revolts and it already had serious overcrowding in its cities. But we can make the case that the drought pushed them over the threshold of resistance.