This story is from Floodlight, a non-profit newsroom that investigates the powers stalling climate action.
Retired Marine Corps gunnery sergeant Vida Rivera knows heat can be as dangerous as any enemy.
Early in her military career, she collapsed from heat exhaustion while carrying a 65lb pack on a sweltering hike in Quantico, Virginia. Years later in Afghanistan, Rivera drove a truck in temperatures nearing 120F (49C). But she was ready. She had taken a mechanics course – twice – to make sure she could fix the truck’s air conditioning if it failed.
She knew extreme heat could incapacitate her marines. “They need water and good temps like everybody,” she said.
Across the US military, the climate crisis isn’t a distant threat. It’s a daily challenge. The fallout from a warming planet has hit the military hard, sidelining more than 10,000 troops with heat-related illnesses since 2018, flooding bases and undermining everything from runways to nuclear readiness.
Extreme weather is battering installations from Guam to North Carolina and fueling instability in regions overseas where American forces may be called to intervene.
For decades, the Pentagon viewed the climate crisis as a national security threat – not for environmental reasons, but because it undermined operations and readiness.
Now the Trump administration is dismantling that approach. Pentagon leaders have cut climate research funding and abandoned adaptation plans. Defense secretary Pete Hegseth has dismissed global warming concerns as “climate change crap”.
Critics warn that the military is being forced to fly blind – and that the cost could be strategic vulnerability in a world where climate is increasingly shaping conflict.
“I think it puts our troops at risk,” said Erin Sikorsky, the director of the Center for Climate & Security. “We’re going to be less prepared if our troops are deployed somewhere where it’s incredibly hot and their equipment doesn’t work right, or if they themselves can’t physically operate … That’s malpractice, I think.”
The Defense Department did not respond to Floodlight’s requests for public documents and an interview to discuss changes to its climate policy.
The Pentagon’s 2026 budget request recommends cutting $1.6bn in “wasteful” climate spending. Among the targeted programs: a $6m grant to decarbonize emissions from navy ships. Where most of the remaining cuts would come from is unclear.
That marked a sharp break from the previous administration, when the Department of Defense sought $5bn for climate initiatives in its fiscal 2024 budget – including efforts to harden bases against extreme weather and reduce battlefield fuel dependence.
How warming undermines US military power
In October 2018, Hurricane Michael struck Tyndall Air Force Base in Florida with 160mph (255 km/h) winds, flipping fighter jets and damaging more than 600 buildings. The branch spent nearly $5bn to repair and upgrade the base to become more resilient to future storms.
And in May 2023, Typhoon Mawar slammed Andersen Air Force base in Guam with 140mph winds and 28in of rain, damaging almost 500 buildings and costing nearly $10bn to repair the base and harden it against future extreme weather events.
According to the National Weather Service, unusually warm ocean temperatures supercharged these storms.
Rising seas also are projected to cause chronic flooding at coastal military bases in the coming decades, with half of coastal bases each facing 270 or more flood events every year, according to the Union of Concerned Scientists.
Major storms can hobble nuclear deterrence, too. Hurricanes could damage submarines or delay the transport of nuclear warheads, warned researcher Jamie Kwong, a fellow in the Nuclear Policy Program at the Carnegie Endowment for International Peace. All three nuclear delivery systems – air, land and water – could be hampered by climate change, she said.
Since 2022, the US military has been deployed to more than 230 climate emergencies, according to the non-profit Center for Climate and Security. And heat-related illnesses among troops jumped 52% between 2020 and 2024.
Much of that work has fallen to the national guard. Over the past decade, the national guard put in nearly 4m days of service responding to hurricanes, floods, wildfires and other disasters, the Pentagon said in a recent report to four Democratic US senators who requested the information.
Fort Benning has long had a problem with excessive heat. Stretching across 182,000 hot and muggy acres in west-central Georgia straddling the Alabama state line, it is one of the army’s top training centers – and has recorded more heat-related illnesses than any other US military base. Until about a decade ago, someone there was dying from the heat every three years.
That crisis led to the 2019 creation of the US army’s Heat Center atFort Benning, where military personnel are taught how to prevent and treat heat-related illnesses.
Officers there developed techniques such as arm immersion – lowering soldiers’ arms into cold water during training breaks to reduce body temperature – and ice sheeting, where frozen bed sheets are wrapped around overheated troops to bring down body heat quickly.
To reduce the risk of heat illnesses, the military generally suspends nonessential outdoor activities on extremely hot days. These so-called “black flag” days – generally 90F or above – are becoming more common, according to a 2023 defense department report.
The military may have to suspend summer training at its hottest bases and “spend a heck of a lot of money” to relocate that training, predicts Caroline Baxter, a former deputy assistant secretary of defense for education and training under Joe Biden.
Military planes and ships are affected, too. Hot, humid air means planes struggle to generate the lift they need. A 2019 Center for Climate & Security brief warns rising heat and humidity will force military aircraft to reduce payloads – or abandon missions entirely.
Warm seawater, meanwhile, makes it harder to cool ship engines, while melting glaciers dilute ocean salinity, which can compromise the effectiveness of sonar.
Retired army Lt Gen Russel Honoré, who led the military response to Hurricane Katrina in 2005, noted that drought caused by global warming helped trigger the Syrian civil war and the armed conflict in Sudan. He has since founded the Green Army, an organization that fights pollution in Louisiana.
“You can change your policy to not consider the impact of global warming on your strategic posture,” Honoré said, but “the heat will cause a disruption to global stability as well as security. And it will continue to have a human impact on our day-to-day training and operational readiness.”
Melting Arctic ice also increases the potential for military conflict, experts say, because it’s opening up shipping lanes that were once inaccessible.
“What that really means is there is an accident waiting to happen,” according to Threat Multiplier, a book by Sherri Goodman, who as deputy undersecretary of defense led the military’s environmental efforts during the Clinton administration.
Mission over emissions: why US military once took climate seriously
The Department of Defense developed its first climate change strategy in 1998 and a decade later declared global warming a national security issue. After Biden took office, the military’s focus on climate impacts took on new urgency.
In 2021, then defense secretary Lloyd Austin called climate change an “existential threat to our nation’s security”, adding its damage “cannot be avoided”.
For the Pentagon, the climate crisis wasn’t just about the environment – it was about how and where troops could operate.
“How do I continue to do my job despite the fact that the operational environment is changing?” said John Conger, a former high-ranking defense department official who later ran the Center for Climate & Security. “You’re not thinking about emissions, you’re thinking about missions.”
In 2022, the army began rolling out its first hybrid tactical vehicles. Hybrids are quieter and consume less fuel, which can save lives in combat.
“We were losing marines and soldiers in the constant movement of fuel to the front in Afghanistan and Iraq,” Goodman wrote in her book. “For every 24 fuel convoys in Afghanistan, one soldier was killed.”
New doctrine: climate doesn’t matter anymore
Donald Trump has pushed to rechristen the Department of Defense as the “Department of War.” And Hegseth has made it clear that the Pentagon’s priorities have shifted.
“The @DeptofDefense does not do climate change crap,” he wrote in a March post on X. “We do training and warfighting.”
On 17 March, Hegseth banned Pentagon agencies from spending money on climate planning, ordering leaders to “remove all references to climate change and related subjects from mission statements”. In his 30 September address to hundreds of military leaders at Quantico, Hegseth declared there would be “no more climate change worship” in the military.
The secretary’s March directive does leave room for the continuation of some weather-related work, including risk assessments, environmental reviews and base resilience improvements.
But the Pentagon also announced it is canceling 91 studies focused on climate and social science research. The move will save $30m – a tiny fraction of the department’s $850bn budget – scuttling research on emerging security threats, including climate change, extremism and disinformation.
Climate action plans from the army, navy, air force and coast guard have quietly disappeared from public websites in recent months. The Pentagon also shut down its climate resilience portal.
Conger, the former Center for Climate & Security director, said: “If you do not have complete information because you willfully ignore certain parts of the puzzle, you put yourself at a disadvantage – because the Russians and the Chinese aren’t ignoring it.”
