Syria and California have both recently suffered their worst-ever droughts, exacerbated by global warming. Syria's may have helped trigger its bloody civil war, but not California's, which instead brought vermin invasions and wildfire. The difference points to the resilience that will be needed in a warming world.
Colin Kelley of the University of California, Santa Barbara, and his colleagues analysed Syrian weather data since 1931, and found steadily less winter rainfall, which is crucial for crops, and higher temperatures, which dry soils faster. The only explanation for such a change over that timescale lies in man-made greenhouse emissions, says Kelley. Climate models, his team found, consistently predict such changes for the Fertile Crescent, the Middle Eastern area that includes Syria and Iraq .
The researchers used a statistical technique to separate the long-term drying that appeared linked to climbing CO2 emissions from yearly, natural ups and downs in precipitation. Those natural variations led to the occasional drought by themselves, says Kelley. But, he adds, "the long-term drying trends exacerbated the recent drought, making it the most severe in the observed record." Crops failed from 2006 to 2009 in Syria's northeastern region that is its breadbasket – then when rains returned, they triggered an explosion of yellow rust, a wheat fungus, that killed up to half the crop.
Since 2011, California has also been suffering its worst drought on recordClimate models do not predict less rainfall for the state, but do forecast that years of naturally low rainfall will be more likely to be unusually warm, sayNoah Diffenbaugh and colleagues at Stanford University. They report that, as in Syria, higher temperatures in recent times have exacerbated the impact of naturally dry years, making them more deadly to crops.
Unlike California, however, Syria tipped into civil war in 2011, which has beenpartly blamed on the drought.
Using satellite images, Kelley's team confirms that over-pumping of ground water in north-eastern Syria because of government subsidies for wheat production depleted a source of irrigation that farmers could otherwise have used when rains failed. Meanwhile, the Syrian government slashed food and fuel subsidies. "This resulted in agricultural collapse and mass migration," says Kelley.
When relief failed to arrive over the next two years – partly, say analysts, because the local mostly Kurdish population opposed Syrian president Bashar al-Assad – up to 1.3 million destitute people fled the north-east and into Syria's urban slums, which already hosted a million refugees from Iraq.
As a result of the drought, grain prices rose 27 per cent between 2008 and 2010, and mass migration into slums with few job opportunities meant that unemployment soared in a mostly young population – a recipe for unrest. Cities affected included Homs and Hama, where protests began in 2011.
Other investigators have linked climate stress and civil unrest . "This is plausible," says Andrew Solow of Woods Hole Oceanographic Institution in Massachusetts. "Placing stress on a society tends to make violence more likely." But he has questioned whether that means such links are always important. The existing political unrest in the Middle East, he observes, might have led to violence in Syria even without a drought .
Kelley agrees there is no one cause for the violence – but cites interviews with Syrian refugees who blamed the drought for "pushing people toward revolution".
Drought-stricken California, meanwhile, has been hit by vermin and wildfire, but no mass migration or violence. The difference, says Kelley, is resilience, the ability of a social system to absorb shocks and still function. "Syria's vulnerability was very high before the drought," he says. "California has much higher resilience." Many societies at risk of climate shocks might benefit from understanding that resilience – and how to bolster it.