For Prime Minister Stephen Harper, national security is a top priority.

Climate change is not.

Yet as a new study suggests, the two are inexorably linked.

More specifically, the study — published Monday in the Proceedings of the National Academy of Sciences — concludes that man-made climate change aggravated the four-year drought that spawned Syria’s civil war.

That’s the civil war, incidentally, that produced the Islamic State, a militant movement that the Conservative government calls a grievous threat to not just Canada but civilization itself.

Certainly, the Harper government is keen on national security.

It is pushing through a bill that, among other things, would give the Canadian Security Intelligence Service extraordinary authority to break the law during its pursuit of perceived villains.

In the name of fighting terror, the government has already passed laws that allow it to limit travel and strip some Canadians of their citizenship.

It has sent Canadian troops and warplanes to battle Islamic State militants in Iraq.

To woo voters for an election set to take place later this year, Harper is putting national security front and centre.

By comparison, climate change is — for this government — a non-issue.

Like the Liberals before them, the Conservatives have done virtually nothing to fight global warming.

In 2008, Harper painted himself as a fan of the so-called cap-and-trade method of limiting greenhouse gas emissions.

Now he derides those who would use cap-and-trade. He calls them wreckers determined to burden the population with job-killing taxes.

He always has an excuse for avoiding climate change.

When oil prices were high, he said that measures to combat global warming would harm consumers.

When oil prices fell, he said such measures were equally impossible: they might harm producers.

Harper routinely lauds Canada’s Arctic while ignoring the fact that its melting ice cap is putting the entire region at risk.

Climate change simply isn’t important to this government. It calculates, perhaps correctly, that the voters don’t care.

But now that climate has been linked to terrorism, this calculus might change.

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As the Star’s Ravenna Aulakh has reported, the authors of Monday’s study are exquisitely cautious in their findings.

They begin from the premise that Syria’s four-year drought, the worst in the country’s recorded history, contributed to the uprising against President Bashar Assad.

That point has been made before. The 2007-10 drought savaged the Syrian countryside, forcing about 1.5 million people into overcrowded towns and cities.

On top of this, Syria was overwhelmed by hundreds of thousands of Iraqi refugees fleeing the chaos sparked by America’s 2003 invasion.

Assad’s encouragement of water-intensive export crops like cotton only aggravated the problem.

But what caused the drought? Here’s where this study breaks new ground. It concludes that human-inspired climate change increased the probability of Syria suffering a cataclysmic drought by a factor of 200 to 300 per cent.

In other words, the country might have experienced a dry spell anyway. But human activity, by warming the Eastern Mediterranean, ensured that any drought which did occur would be significantly worse.

Wisely, the study’s authors don’t conclude that the Islamic State is the inevitable result of global warming. They recognize that while climate change might aggravate political conflict, it is impossible to predict which forces will emerge from the chaos.

Still, for those of us who are interested in figuring out why things happen, the findings are instructive.

We already know that dangerous, armed groups thrive in times of crisis. We know that natural disasters such as droughts can aggravate or cause such crises. And now we have evidence that human-inspired climate change contributes to natural disasters.

If Canada’s politicians really want to make the world more secure, they may want to think about this. They may want to focus not only on anti-terror bills. They may want to look beyond misguided teenagers and malevolent websites.

They may also want to address a far more pernicious enemy, one that can turn countries upside-down. Climate change.

Thomas Walkom's column appears Wednesday, Thursday and Saturday.

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