When it comes to climate change impact, few institutions have cast a longer and heavier shadow than the United States military. Its footprint extends far beyond geopolitical frontiers, reaching into the very atmosphere that sustains us. Now, a new study reveals just how consequential this influence is and how small shifts in policy could have planetary effects.

The study examines nearly five decades of data to uncover a striking asymmetry: reducing U.S. military spending slashes energy consumption and carbon emissions more effectively than increasing it drives them up. The authors say that even modest, sustained cuts could lead to annual energy savings equivalent to the consumption of entire countries.

“We show that sustained cuts to U.S. military expenditures could result in annual energy savings on par with what the nation of Slovenia or the U.S. state of Delaware consumes annually by 2032,” write the authors, led by sociologist Ryan Thombs of Penn State University.

A Global Polluter in Uniform

The U.S. military is the single largest institutional emitter of greenhouse gases in the world. Between 2010 and 2019, it released 636 million metric tons of CO₂, which is more than many countries. If it were a nation, it would rank 47th globally, ahead of Sweden and Portugal.

And these numbers likely undercount the true emissions. They omit indirect, or Scope 3, emissions such as those from the military’s supply chain, travel, and waste. And they also don’t account for the CO₂ released when bombs fall, forests burn, or pipelines explode during conflicts.

“We started this study not entirely sure what we were going to find,” Thombs told Newsweek. “The finding that cutting expenditures had a larger impact than increasing expenditures was a little bit surprising but made sense, and it is also the thing that really stood out in our analyses.”

That asymmetry is key. While more funding means more jets flying, more ships deployed, and more bases maintained, cuts seem to trigger sharper operational constraints. The biggest reductions came from decreased use of jet fuel.

Over the last fifty years, jet fuel has accounted for more than half of all U.S. military energy use. Scaling back the military’s air operations, especially long-distance flights and combat exercises, has outsized effects on energy consumption.

“Aviation is very energy-intensive, and any serious effort to reduce the military’s footprint will require focusing on this category,” Thombs told BBC Science Focus. “Reducing the scale of aviation operations is imperative to reducing emissions.”

A Forecast with Real-World Stakes

To better understand what future military decisions might mean for the planet, the researchers projected energy use under various budget scenarios through 2032.

If military spending were to decrease by 6.6% annually, a rate seen before in U.S. history, by 2032, the Department of Defense (DoD) could be using 272 trillion fewer BTUs (British Thermal Units) of energy annually, roughly equivalent to the energy needs of Slovenia. Even more modest annual cuts of just 2.3% would still save enough energy to match the usage of Vermont or Estonia.

Conversely, large annual increases—like the 13% hike proposed by President Trump’s administration—could add the equivalent of El Salvador’s or Washington, D.C.’s total annual energy use to the military’s footprint.

Yet even the study’s lead authors acknowledge that politics may trump science (no pun intended).

“The most impactful way to reduce the social and environmental costs and harms of the military is to scale it back,” Thombs said. “I believe it could be a winning strategy to frame the cuts in this way, as reinvesting these funds could materially improve people’s lives.”

Some lawmakers agree. In recent years, senators like Edward Markey and Bernie Sanders have proposed slashing the Pentagon’s budget by 10%, redirecting the funds toward jobs, healthcare, and education.

The Carbon Ripple Effect

The implications of these findings stretch far beyond U.S. borders. As military budgets swell globally, spurred by war, insecurity, and political ambition, so do emissions. In 2024, global military spending reached $2.7 trillion, marking the steepest rise since the Cold War.

Military operations have long been exempt from international climate agreements. That carveout dates back to U.S. lobbying during the Kyoto Protocol negotiations in the 1990s. “We took special pains … to fully protect the unique position of the United States as the world’s only superpower,” said then–State Department official Stuart Eizenstat.

But experts now warn that this policy of exceptionalism comes with a cost.

“If Trump follows through with his threats, U.S. military emissions will absolutely rise, and this will cause a ripple effect,” said Neta Crawford, co-founder of the Costs of War project at Brown University, in an interview with The Guardian. “The allies or former allies of the U.S. have increased their military spending, so their emissions will go up. As adversaries … increase their military activity, their emissions will go up. It’s very bad news for the climate.”

Crawford’s research shows that over the last 45 years, the Pentagon has generated nearly 4,000 million metric tons of CO₂, roughly equal to the entire emissions of India in a single year.

And these figures still exclude the emissions from weapons manufacturing, post-conflict reconstruction, and war-related environmental destruction like deforestation, burning oil fields, or disrupted ecosystems.

Can the Military Green Itself?

The Pentagon has, at times, acknowledged the threat climate change poses to national security. As far back as 1991, President George H.W. Bush described global warming as a strategic concern. And in 2022, the U.S. Army pledged net-zero emissions by 2050, promising to electrify its vehicle fleet and transition bases to renewable energy.

Yet in the current political climate, those commitments have stalled or reversed. In March, Defense Secretary Pete Hegseth dismissed climate programs as irrelevant. “The @DeptofDefense does not do climate change crap,” he posted on X. “We do training and warfighting.” Well, that’s encouraging.

Critics say this stance is shortsighted. Hurricanes have already destroyed key bases, and climate-fueled droughts and flooding are destabilizing entire regions, which in turn drive new conflicts—and new deployments.

“If they really believed their own rhetoric,” said Crawford, “they would of course work to reduce their contribution to climate change by reducing emissions. The irony is difficult to stomach.”

A Fork in the Road

The study’s authors are cautious about overpromising. Their work shows strong correlations, not direct causation. They don’t break down spending by specific branch or weapons system, and their findings may not generalize beyond the U.S.

Still, the message is clear: military budgets are not just economic or security decisions. They are also climate decisions.

In a world on edge, it’s tempting to meet every threat with more weapons, more jets, more force. But the new research suggests that might also mean more heat, more floods, and more instability in the long run. In a war with nature, we’ll always be on the losing side.

“We find that reductions in spending are associated with reductions in energy consumption from military facilities, vehicles, equipment, and jet fuel in particular,” Thombs said.

The new findings appeared in PLOS Climate.