A tangled knot of overlapping causes led to the bloody chaos that grips Syria today. But some of them have received more attention than others.

The match that set the country aflame—the Syrian government’s brutal suppression of Arab Spring protests in early 2011—has gotten plenty of coverage. But beginning in 2006, years before the first demonstration got underway in Daraa or the first shot was fired in Damascus, there was drought. But it wasn’t a typical drought. It was an extended dry spell that one expert characterized as “the worst long-term drought and most severe set of crop failures since agricultural civilizations began in the Fertile Crescent many millennia ago.”

According to Francesco Femia, director of the Center for Climate and Security, herders in the Northeast of the country saw 85 percent of their livestock get wiped out. In many of the Syrian communities that were most dependent on agriculture, 75 percent of farmers experienced total crop loss.

The drought, which had been aggravated by years of resource mismanagement by the regime of Bashar al-Assad, was a major shock for a society that already had a lot of social friction—ethnic, political and economic tensions that had long been percolating beneath the surface.

Food prices skyrocketed. People went hungry. And roughly two million Syrians who were reliant on agriculture–around 10 percent of the population–saw their livelihoods destroyed, and had to get up and move. Most of them ended up in urban areas like Homs and Damascus, cities with poor infrastructure that was already straining under the pressure of refugees flowing in from Iraq and elsewhere.

Privation and hopelessness brought a huge number of Syrians out into the streets, and ultimately led to the devastating civil war that continues today. That conflict then opened the door to ISIS’s encroachment and rapidly expanded into a regional proxy war.

Femia cautions that it’s hard to say exactly how much Syria’s epic drought contributed to the outbreak of fighting, largely because it’s almost impossible to study the issue while the bloodshed continues. But he points out that before the revolution, Syria “was widely perceived as being stable and not susceptible to the same kind of pressures we saw in Tunisia and Egypt. And one of the reasons [the conflict took people by surprise] is that these environmental stresses were largely ignored by traditional security analysts.”

But we do have an idea of the role human-caused climate change played in Syria’s environmental disaster. A 2011 study by the National Ocean and Atmospheric Administration (NOAA) found that, in large part due to human activity, 10 of the 12 driest winters on record in the Mediterranean region (which gets most of its precipitation during the winter months) occurred in the past 20 years. And earlier this year, UCSB climatologist Colin Kelley and his colleagues found that greenhouse gas emissions had “increased the probability of severe and persistent droughts in this region, and made the occurrence of a 3-year drought as severe as that of 2007−2010 two to three times more likely than [would be predicted] by natural variability alone.”

The really bad news, says Femia, is that “when we look at the future of the region, the models say that we’re going to see yet more precipitation declines and more of these kinds of drought events. The rate of change is much faster than it has been in the past, and that’s something that we just don’t have any experience with, and the people in the region don’t have any experience with it either.”

Even more worrisome is that many defense experts–both here and abroad–see Syria as a sort of case study for the kinds of conflicts that we’re likely to see more frequently as the Earth continues to warm. “The impacts of climate change have increasingly entered the mainstream of defense and security discussions, ” says David Titley, who rose to the rank of Rear Admiral as the head of the US Navy’s Meteorology and Oceanography Command before becoming the director of Penn State’s Center for Solutions to Weather and Climate Risk. “If you raise the question of what we should be doing as the climate changes, people no longer ask, ‘why are you talking about this?’ Policy people are asking what might be the next shoe to drop. They’re wondering what might take us by surprise.”

In 2014, the Defense Department released its “Climate Change Adaptation Roadmap,” describing the issue not as a long-term concern, but something that “poses immediate risks to U.S. national security.” The Defense Department sees the changing environment as a “threat multiplier” which will exacerbate existing security issues. According to the DoD’s roadmap, “Rising global temperatures… will intensify the challenges of global instability, hunger, poverty, and conflict.”

That worries Christine Parthemore, who spent five years at the Pentagon as a senior advisor to the Assistant Secretary of Defense for Nuclear, Chemical, and Biological Defense Programs before founding a consulting firm called CLP Global LLC. “Armed conflict on a large scale has been on a decline for decades and decades,” she says. “We’re not in the world war era anymore, but people are fighting and dying and at war all over the world in ways that we don’t really consider warfare in the same way. I’m really concerned about the effects on food supplies, and how that can lead to social unrest, the movement of people, people rioting and that sort of thing.”

Parthemore also worries about “increasing urbanization–especially in Asia but in parts of coastal Africa as well–colliding with the effects of sea-level rise. That not only threatens billions of dollars of infrastructure, but also leads to people moving or being forcibly relocated. And when things like that happen in countries with existing social cleavages–along ethnic or tribal lines–that’s where social tensions tend to get exacerbated by environmental effects in ways that can lead to armed conflict.”

David Titley notes that those kinds of impacts can sometimes be felt “half a world away.” During the Arab Spring, “we saw wheat prices going up and one of the drivers of that was simultaneous droughts in Russia and Australia, which drove up commodity prices. But we didn’t see the instability manifest itself in Russia or Australia–we saw it in North Africa, where they import huge amounts of wheat and don’t have a lot of disposable income.”

Defense analysts worry that countries like Nigeria and Mali–where terrorism is on the rise and rapid population growth may soon collide with environmental changes–will follow suit. They worry about the potential destabilization of China, which has built its mega-cities in coastal areas that may not be above water in a few decades. And they worry about how countries in the South China sea that are now fighting over various chunks of rock that are barely above sea level will react when those territories disappear.

But for the United States, arguably the most pressing concern is in our backyard–or Sarah Palin’s backyard. The rapidly receding Arctic icepack has unlocked vast reserves of natural resources, and with them have come conflicting territorial claims by the United States, Russia, Canada, Denmark and Sweden.

Russia has moved aggressively to beef up its military capacity in the region. David Slayton, a decorated former Navy Commander who now analyses energy and security policy at The Hoover Institution, explains that Russia’s onshore energy resources have “moved past peak production, so they’re pushing their energy development offshore, and they’re guarding their investments with a greater military presence. They’re repurposing, resupplying and reinvigorating a lot of their former bases, as well as building new infrastructure everywhere from Murmansk all the way over to the East Siberian Sea.” Titley says it’s highly unlikely that this growing friction in the region could lead to a shooting war. “But does the Arctic get sucked into a broader disagreement?” he asks. “If we have tensions in the middle latitudes, does that get reflected in, say, how Russia conducts its arctic policy?”

These are the kinds of questions that occupy the national security establishment. But Christine Parthemore says, “The biggest thing I worry about is the things I don’t know. Projections have gotten a lot better, but the earth is changing a lot faster than our models had indicated by about a decade. So I worry most about those climate change effects that we think we know about either becoming accelerated or driving new problems that we aren’t even watching for.”

Characterizing climate change as a national security threat has met with some resistance on Capitol Hill. Last year, House Republicans amended the National Defense Authorization Act to prevent the military from using tax dollars to study the issue or mitigate its potential impacts. But defense experts interviewed by The Nation say the Pentagon has heard about how environmental changes are impacting its operations from the rank-and-file–from the Unified Combatant Commands that represent the front lines of US military operations. With heavy pushback from the defense establishment, the amendment was killed during reconciliation.

All of the analysts interviewed by The Nation said that while the military is taking the threat of climate change seriously, Congress hasn’t given the Pentagon the funding to match the scope of the threat. It will require significant new investments, which is a tough sell in a budget environment marked by endless partisan showdowns and sequestration.

But, as Parthemore says, “we’re talking about the sort of things that we’re going to have to deal with in the decades to come, regardless of what kind of deal we get [in the upcoming COP21 climate negotiations] in Paris. I tell people that while we haven’t had a vote on it, this is a carbon tax that we’re paying. One way or another, we’re going to have to fund this.”