A new study has revealed the astronomical scale of the US military’s carbon footprint – and how relatively modest budget cuts could significantly reduce it.
Published in the journal PLOS Climate, the research found that US Department of Defense (DoD) spending is tightly linked to energy consumption and greenhouse gas emissions. Reducing military expenditure, the authors argue, could yield dramatic benefits for the planet.
The US military is the largest emitter of greenhouse gases of any institution on Earth, generating an estimated 636 million metric tons of CO₂ equivalent (a standardised measure of greenhouse gas emissions) between 2010 and 2019.
If it were a country, this would make the US military rank 47th globally in emissions, ahead of nations like Sweden and Portugal.
And that’s just the tip of the iceberg. These figures only include what’s known as Scope 1 and 2 emissions – direct emissions from fuel combustion and purchased electricity. They exclude indirect (Scope 3) emissions from employee travel, waste disposal, and the supply chain, meaning the true footprint is higher.
Using publicly available data from 1975 to 2022, the analysis, led by Prof Ryan Thombs of Penn State University, in the US, sought to identify a link between military spending and energy consumption (and, therefore, greenhouse gas emissions).
Unsurprisingly, increases in spending led to higher energy use, while cuts caused it to fall. However, a puzzling – and promising – asymmetry was found between the two: reductions in spending had a significantly larger impact on energy consumption than increases did.
“We find that reductions in spending are associated with reductions in energy consumption from military facilities, vehicles, equipment, and jet fuel in particular,” Thombs told BBC Science Focus.
“Although future research is needed to investigate the specific mechanisms, these findings suggest that spending cuts may place greater pressure on the military to reduce the scale, distance, and frequency of movement of machinery, goods, and personnel than increases in spending do to increase these activities.”
Another likely reason for this trend, Thombs added, is that budget cuts may disproportionally reduce aviation activity.
Globally, military jets are among the most energy-hungry machines in operation – and in the US military, jet fuel accounts for 55 per cent of total energy use over the past half-century.
“Reducing aviation activities must be a key focus given its share of energy consumption," Thombs said. “Aviation is very energy-intensive, and any serious effort to reduce the military’s footprint will require focusing on this category.”
Curbing emissions from aviation is notoriously difficult. Both military and commercial aviation are considered “hard to abate” sectors, where existing technology cannot yet substitute fossil fuels at the required energy density or scale.
This, Thombs said, “suggests that reducing the scale of aviation operations is imperative to reducing emissions.”
The team also produced forecasts for various future budget scenarios. They found that if military spending were reduced by 6.59 per cent each year from 2023 to 2032 the DoD’s annual energy savings would be equivalent to the total energy use of the entire country of Slovenia, or the US state of Delaware. The military has seen such rates of reduction before over the last five decades, so – though this is at the higher end of typical budget cuts – it is, in theory, possible.
But while the science on this is clear, the politics is anything but. Governments around the globe are spending more and more on defence in a world increasingly rocked by conflict and instability.
On 26 June, President Trump’s administration proposed a $1.01 trillion national defence budget for the next fiscal year – a 13.4 per cent increase on the year prior.
Despite this trend, Thombs is optimistic that, given the correct framing, spending cuts are feasible. He pointed to previous proposals from Senators Edward Markey and Bernie Sanders to slash military spending by 10 per cent, with the money redirected to jobs, healthcare and education.
“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,” Thombs said. “The most impactful way to reduce the social and environmental costs and harms of the military is to scale it back.”
The researchers now plan to investigate why spending cuts appear to yield such outsized savings, and whether the same pattern holds true for other major militaries.
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About our expert
Ryan Thombs is an assistant professor of rural sociology in the Department of Agricultural Economics, Sociology and Education at Penn State University, in the US. His published research appears in leading sociology journals such as the American Sociological Review, Sociological Methodology, the Journal of Health and Social Behavior, and Socius, and various high-impact interdisciplinary journals, including Global Environmental Change, Energy Research & Social Science, Climatic Change, and Environmental Research Letters.