President Donald Trump has made his fixation on Greenland abundantly clear—enough so to unnerve many of the people who live there. “I think Greenland is going to be something that maybe is in our future,” he told reporters this week, once again teasing the notion of annexation. Vice President J. D. Vance is traveling there today, after what he called the “excitement” around his wife’s plan to attend a famous dogsledding race. As part of the trip, National Security Adviser Michael Waltz and Energy Secretary Chris Wright were scheduled to visit a U.S. military base; Greenland’s prime minister, Mute B. Egede, called the visit a “provocation.” Now dogsledding is out, and the entire delegation will together travel to the base.

Their aim, the vice president said in a video on X, is to check up on Greenland’s security, because unnamed other countries could “use its territories and its waterways to threaten the United States.” And these are real concerns for the United States, rooted in climate change: As polar ice melts away, superpowers are vying for newly open shipping routes in the Arctic Ocean and largely unexplored mineral and fossil-fuel reserves. Arctic warming could pose a direct threat to America’s security interests too: Alaska could have new vulnerabilities to both China and Russia; changes in ocean salinity and temperature might interfere with submarine detection systems; the extremes of climate change, including permafrost thaw in Russia, could drive economic instability, social unrest, and territorial claims.

During the Biden administration, the U.S. military and NATO had both started to treat global warming in the Arctic as a matter of real military concern. Whether that will continue under Trump is an open question. Even as the president has tried to erase U.S.-government action on climate change, when he talks about Greenland, he’s tacitly acknowledging that rising temperatures are rapidly changing that part of the world—and U.S. interests there.

“This is a threat environment we haven’t encountered in living history,” Marisol Maddox, a climate-security specialist at Dartmouth’s Institute of Arctic Studies, told me. For decades, the world’s response to climate change has been one of prevention, driven by scientists and diplomats. The Trump administration is openly rejecting that approach. But as the more dramatic impacts of climate change become reality, even a president who wants to ignore its risks may have no choice in the matter.

In recent years, the world’s largest military apparatuses—the U.S. Department of Defense and NATO—have added climate change to their war games. Both DOD and NATO have started regularly assessing how climate risks could affect both military and civilian security, and NATO opened the Climate Change and Security Centre of Excellence in Montreal. In the U.S., national intelligence agencies “are thinking about strategic surprise” from climate change, Julie Pullen, a climate scientist who’s part of a congressionally mandated advisory group of climate-security experts, told me. Just as, for instance, the Defense Intelligence Agency might have to weigh the possibility that Iran might one day have nuclear weapons, intelligence officials should consider the nonzero chance of the Eastern Seaboard going underwater, she said.

A handful of other countries—Germany, Australia, Japan, and several small island states—also have a policy for climate security, and many NATO states refer to such aims in their security agenda. But the U.S. has been leading the world in thinking seriously and systematically about these realities. Although this shift happened during the Biden administration, Sherri Goodman, who served as the deputy undersecretary of defense for environmental security, told me that in the U.S., this push had been a nonpartisan effort and that for the military, “it’s all about risk.” She’s seen four-star generals go from treating climate change with skepticism to facing it like any challenge the military must prepare for.

The second Trump administration doesn’t exactly see it that way. After CNN reported on DOD plans to cut climate programs earlier this month, for instance, Defense Secretary Pete Hegseth affirmed on X, quite bluntly, that the department “does not do climate change crap.” References to climate change have been fast disappearing from major agency websites—including the entire Department of Defense Climate Resilience Portal. In response to a request for comment, a DOD spokesperson told me that the department “is eliminating climate-change programs and initiatives” and that “climate change is not part of the department’s warfighting mission nor the president’s priorities.”

But the logic of climate security still holds. As the region’s ice-covered buffer zone opens up, “we need to be very mindful of the changes that are taking place, and posture to respond,” Iris Ferguson, a former U.S. deputy assistant secretary of defense for Arctic and global resilience, told me. Until now, the world has opted to respond to such changes by trying to reduce emissions through climate diplomacy. But those reductions aren’t happening as climate diplomacy promised. In fact, in October 2024, a United Nations report found that atmospheric carbon dioxide was increasing “faster than any time experienced during human existence.” At some point, the U.S. military might start to consider its own, more direct options for responding.

Assuming that greenhouse-gas emissions keep rising, scientists predict that climate change will have abrupt, irreversible effects on the planet—the only question is when. For instance, they’ve been tracking the potential slowdown of the Atlantic Meridional Overturning Circulation, an ocean-circulation mechanism that regulates global temperatures. If the AMOC eventually collapses, sea levels along parts of the East Coast could rise by up to a meter, and temperatures across Europe could drop dramatically, disrupting the global food supply. (Agriculture in Great Britain, for instance, could be largely wiped out.) Scientists are still debating if and how quickly the AMOC’s collapse might occur, but recently some have begun to warn that it could happen within just a few decades.

If the world is heading that rapidly toward an irreversible tipping point, “that’s where climate interventions start to make a lot of sense” for the U.S. government, Pullen told me. Sandia National Laboratories, the Albuquerque lab dedicated to national security, is investigating technologies that could slow down or reverse the rise of global temperatures. Scientists and engineers from the lab have, for instance, simulated the effects of releasing several million metric tons of sulfur dioxide from planes circling above the Arctic. Those chemicals would reflect sunlight, casting a cooling shade over the planet’s surface and dropping temperatures over several decades. Eventually, some Arctic sea ice might be restored too. (The Department of Energy, which oversees Sandia, did not comment on whether these efforts would continue in the Trump administration.)

To date, the scientific community has largely rejected geoengineering as an overly risky gamble. And injecting chemicals into the stratosphere does present serious ethical and governance challenges. This plan is impossible to test at scale before deploying, rendering most consequences both unknown and possibly irreversible. Any kind of responsible management would require unprecedented international cooperation, potentially including a new multinational body to govern geoengineering. As President Trump casts doubt on NATO, that level of global cooperation seems less likely all the time. And if injections stopped (whether because governance or the technology itself failed), many models suggest that the world could plunge into “termination shock”—rapid global heating with consequences potentially worse than if we’d never used this strategy at all.

Sandia’s simulations are just that: simulations. But Maddox believes that the U.S. government should continue exploring even the most drastic options. Failing to mitigate climate change increases the odds “that we’ll have to rely on a technology that’s pretty extreme,” she said. “When multiple catastrophic events converge at the same time and public outcry reaches a panic level, the government must be ready with options.”

So far this term, Trump has acted as if climate change does not matter: He has withdrawn from the Paris Agreement, announced plans to reopen the Arctic National Wildlife Refuge for oil and gas drilling, and paused new offshore-wind development and Inflation Reduction Act clean-energy funding. But if the president’s bid for Greenland—or the U.S. military’s quiet cooperation with Canada to boost Arctic defenses—is any indication, the U.S. is weighing its options for a warmer future. “We live in the real world,” Evan Bloom, a global fellow at the Wilson Center’s Polar Institute and former State Department official, told me. “The military and other agencies will continue to take climate change into account, because they have to.” When he hears Trump talk about Greenland, he hears the president speaking about the geopolitics of climate change—“whether he’s willing to call it that or not.”