Toward the end of last week’s Democratic debate, CNN anchor Anderson Cooper tossed the five candidates on stage a relative softball: "What is the greatest national security threat to the United States?" he asked.

The chaos in the Middle East, Governor Lincoln Chafee offered meekly. Nuclear Iran, said former Maryland governor Martin O’Malley. The spread of nuclear weapons and the risk of them falling into the wrong hands was former Secretary of State Hillary Clinton’s answer. And Senator Jim Webb crammed three answers into his response: China, cyber warfare, and the “situations in the Middle East.”

But Vermont Senator Bernie Sanders, never one to let a lack of consensus stand in his way, broke from the pack. His nomination for the biggest national security issue: climate change. That earned Sanders derision from Republican candidates like Mike Huckabee and public praise from supporters like Seth MacFarlane. Still, it was just one answer in a two and a half hour debate, and was quickly overshadowed just minutes later when Sanders told Cooper that America was sick of hearing about Clinton’s “damn emails.”

But while the national security comment may have been fleeting, the fact that climate change was brought up in that context at all signals a much bigger shift in how politicians are framing the issue—a shift that's been years in the making.

Though talk of climate change was notably absent from the 2012 debates—which caused critics to accuse both President Obama and Mitt Romney of "climate silence"—it's been a fairly steady fixture of presidential debates for decades, discussed in nearly every debate cycle since 1988. Candidates have framed it as an economic issue, an environmental issue, and a public health issue. But only recently have politicians like Sanders—and even President Obama himself—elevated climate change to the seriousness of national security.

Just this year, President Obama—who back in 2008 was praising green jobs as a key to the country's economic recovery—told graduates of the United States Coast Guard Academy that “climate change constitutes a serious threat to global security," which will "impact how our military defends our country.”

Both Obama and Sanders have a point, of course. Climate change activists and military minds have been sounding the alarm on this issue since the early 2000s. But if concern over the climate moves from the academic and scientific spheres to the political, that'll have important implications for how the country responds. And old-line environmentalists may not always like it.

From Syria to the Arab Spring

Back in 2003, the Department of Defense issued a report called "An Abrupt Climate Change Scenario and Its Implications for United States National Security." It posited that climate change could lead to food shortages and drought, which can exacerbate instability in vulnerable countries. But according to Francesco Femia, founding director of the Center for Climate and Security, that report was easy for people to ignore; the first of its kind, it positioned climate change as a far-off threat.

Since then, however, defense and intelligence agencies have concluded that climate change—and its ensuant upheaval—could be a more immediate threat. A Council on Foreign Relations paper in 2007 offered specific recommendations on how to mitigate risk. Another report in 2008, commissioned by the CIA, attempted to predict climate change's impact on national security by the year 2030. By 2014, the Department of Defense had adopted the term "threat multiplier" to describe climate change, and put out its so-called Climate Change Adaptation Roadmap, which surveyed the vulnerability of the country's military bases, and included input from its Combatant Commands around the world.

Meanwhile, research began to reveal how climate change contributed to the Arab Spring and the conflict in Syria.

All of this, says Femia, who co-authored a report on the Arab Spring, "raised the bar on the issue" in political circles, particularly among Democratic leaders. "We’ve seen very clear evidence that climate change is already impacting security in a number of places around the globe, including strategically significant places like Syria," he says.

"It's not just a framing. It's not just a message," Femia adds. "It's coming very much from the analysis that our military and intelligence community has been doing over the past decade."

Breaking the Deadlock

Of course, just because this issue is getting legitimate research attention doesn't mean that attention isn't also politically expedient. Over the last decade, climate change has become as partisan an issue as guns and abortion, says Joshua Busby, an associate professor of public affairs at the University of Texas, who authored the Council on Foreign Relations 2007 report. "That’s disastrous for this problem," Busby says.

Framed as an economic issue, Democratic leaders had no choice but to argue that investments in alternative energy would create new jobs, even as Republican leaders warned that retreating from fossil fuels would decimate existing jobs. When evidence of the national security implications of climate change began to surface, Busby says, activists thought, "Maybe Republicans might be more open to thinking of climate change as a real problem if it’s brought to them by people they trust on national security."

The Citizens United decision, which enabled donors to pour unlimited money into campaigns, also amplified the influence that billionaire environmentalists like Tom Steyer and his Super PAC NextGen Climate Action could have on pushing the issue. In the 2014 election cycle, NextGen Climate Action spent nearly $74 million to promote environmental issues. That, Busby says, has made advocating for climate action more "politically advantageous for Democrats," because there's money behind the cause.

Be Careful What You Wish For

Framing climate change as a national security threat has obvious advantages. Not only does it increase the sense of urgency, but it also creates a path for environmental solutions. The military, for instance, could play an important role in building advanced green technology, helping secure the country's grid and giving the US a strategic advantage over other countries in the future. "Once we recognize it as an issue that affects all sectors of society including the security of our political institutions, governments, and communities, then we can tackle it in a much more holistic way," says Femia.

But while the security implications of climate change are real, both Femia and Busby say it's crucial not to raise too many alarms. Femia, for one, takes issue with Sanders' assertion that climate change is the biggest national security risk today. "I think that framing is problematic. It doesn’t compete with other priorities, things like terrorism or the nuclear threat of Iran or North Korea," he says. Ignoring that fact, Femia says, will only make it easier for candidates on the other side of the aisle to write off the issue entirely. "It's going to be really important in the future to talk about climate change as not the biggest security issue, but an issue that will make security harder in the future," he says.

Then there's the fact, says Busby, that framing climate change as a military issue could lead to military solutions, not environmental ones. For instance, sea ice melting in the Arctic has paved the way for new drilling opportunities for countries like Russia. Of course, climate mitigation activists know that more drilling won't fix the problem. But faced with the increased presence of countries like Russia in the region, President Obama recently called for new investment in Arctic icebreakers, which will help the US Coast Guard defend its oil interests in the region against other countries.

In other words, when you frame climate change as a security threat, the military will want to respond. And the way they will respond may have very little to do with stopping the spread of climate change. It will have to do with protecting military interests. "All that comes at a cost," both environmental and monetary, Busby says.

Which is why, he says, politicians should think long and hard before recasting the issue of climate change completely. "People who are proponents of using the security framework to attract attention to this issue might not anticipate that when the military takes something seriously as a security threat, it has certain implications for the military," Busby says. "It reinforces nationalistic responses to solving the problem, as opposed to collective efforts that might be mutually beneficial to the world."