Secretary of Defense Pete Hegseth says the military will trim eight percent from its budget in each of the next five years.
In a recent news conference, he named an early target.
"Look at a lot of the climate programs that have been pursued at the Defense Department," Hegseth said. "The Defense Department is not in the business of climate change, solving the global thermostat. We're in the business of deterring and winning wars."
Military planners had long incorporated thinking about climate change into their work, but that increased sharply after President Joe Biden signed an order in 2021 underlining climate change as a national security concern. One of President Trump's first actions rescinded Biden's order.
But national security experts say the Pentagon's climate change programs are actually all about warfare.
"There's essentially nothing that the Department of Defense is doing related to climate change that is only a purely environmental purpose," said Tom Ellison of the Center for Climate and Security in Washington, D.C. "It always comes back to accomplishing their mission."
In part, that's because the military has to plan decades ahead for much of what it does, he said. In coming years, sea-level rise is expected to swamp some coastal installations. Rising temperatures will increase the number of days it's too hot to train outside.
Climate change likely will force changes to ships and military equipment, and it's likely to shape the nature of combat and where conflicts occur.
"If you want a capable and healthy U.S. military and fighting force, you need to understand things like: How is extreme heat and pollution affecting the health of your troops?" Ellison said. "When climate change changes the chemistry of the ocean, how is my submarine sonar going to work differently, which it will? How will changes in humidity affect the the lift capacity of my transport aircraft? How will climate change affecting crop yields cause food price spikes and instability?"
Ellison says even things like making military vehicles more fuel efficient are about warfighting.
"That's something that has environmental benefits," he said. "But the driving force behind why the DoD is interested in things like that is to reduce the logistics tail of their operations. When you had troops in Iraq and Afghanistan getting killed delivering fuel supplies to forward operating bases, if you use less fuel and you need less fuel, you have less of a need for that," he said.
Climate change has also prompted the military to build more resilience into its infrastructure planning.
Increasingly common and more powerful storms have severely damaged installations, such as Camp Lejeune, North Carolina, where Hurricane Florence in 2018 damaged more than 300 buildings. The Marine Corps spent $3.6 billion dollars on repairs and new construction.
Key coastal installations in places like Norfolk — home of the world's largest naval base and several other military installations — experience regular flooding. The means things like new barracks and piers have had to be redesigned for higher sea levels.
And experts say some installations – like the Marine Corps' iconic Parris Island, South Carolina – eventually will have to be abandoned and their missions shifted elsewhere, which will take elaborate and lengthy planning.
Ellison also noted that state national guards and active duty units are increasingly called upon to respond to catastrophic damage from the kinds of disasters that climate change is making more frequent. His group just issued a report that tallied 176 military responses across the nation to floods, fires, and hurricanes since 2022.
Because dealing with the effects of climate change is such a practical issue for the military, its efforts generally have received support from both parties in Congress.
"This recognition of climate change as a national security issue has traditionally been kind of a rare right spot, an area of bipartisan treatment of climate change," Ellison said.
It's early in the budget-cutting process, but one sign of what might come is the disappearance of an official website that helped military leaders plan for a changing climate. It was called the Department of Defense Climate Resilience Portal.
The Defense Department didn't respond to questions about why the portal was taken down and what climate-related programs will be eliminated.
Caroline Baxter, now retired from the Defense Department, oversaw the portal's creation in her role as Deputy Assistant Secretary of Defense for Force Education and Training.
"That portal was meant to give people resources and one place to go for those resources," she said, "I'm a logistician. What do I need to know about changing sea level rise? How do I make a decision about that? I'm an installation manager. How is sea level rise going to affect any expansion of the installation that I'm supposed to manage?"
The effects of climate change, she said, have impacts that civilians might not think of, such as whether the cooling systems for aircraft carriers are adequate for seas with rising surface temperatures. Or whether changing salinity from melting polar icecaps reduces the effectiveness of submarine-finding sonar.
The name of the portal, she said, was chosen carefully.
"It wasn't climate change, it was climate resilience," she said. "Our goal was to ensure that Airmen, Marines, Guardians, coast guardsmen, soldiers, all of them, that their mission was the most important thing, and to the extent that anything they did was of benefit to the climate was completely ancillary."
Baxter says military planners can't ignore the information the portal provided without a cost.
"There is a math and physics about climate change, and that has been true for decades," she said, "that has made what they do harder and will continue to make what they do harder."
This story was produced by the American Homefront Project, a public media collaboration that reports on American military life and veterans.
