The US military is the single largest institutional consumer of petroleum on Earth, burning through roughly 4 billion gallons of fuel a year, so much that if it were a country it would rank among the world's fifty-odd biggest greenhouse-gas emitters, ahead of entire nations like Portugal and Sweden.

There are roughly 195 sovereign countries on the planet. Each one has an energy budget. If you rank them all by the amount of fossil fuel they consume each year, the results are more or less what you’d expect. The largest economies come out at the top, the smaller ones further down. And roughly two thirds of the way through the ranking, sitting between Peru and Portugal in terms of total liquid fuel purchased annually, is a single institution that isn’t a country at all. It’s the United States Department of Defense.

The scale

According to a November 2019 paper published by Brown University’s Costs of War project, authored by political scientist Neta C. Crawford (now Professor of International Relations at the University of St. Andrews and winner of the 2024 Grawemeyer World Order prize for her subsequent book on the same subject), the US military consumes between 77 and 80 per cent of all fossil fuel energy used by the entire US federal government. In fiscal year 2016 the Pentagon burned through approximately 86 million barrels of liquid fuel, which works out to a little over 3.6 billion gallons. In other years the figure has been closer to four billion. The largest single component is jet fuel, primarily for the roughly 5,000 military aircraft the US operates worldwide.

What that actually looks like in the air

The consumption profile at operational scale is genuinely difficult to grasp intuitively. A KC-135 Stratotanker, the workhorse aerial refuelling aircraft the Air Force has been flying since the 1950s, consumes approximately 4.9 gallons of jet fuel per mile in flight. That’s per mile, not per hour. In January 2017, Crawford’s paper documents, two B-2 stealth bombers plus fifteen aerial refuelling tankers flew a 12,000-mile round trip from Whiteman Air Force Base in Missouri to bomb ISIS positions in Libya. That single mission, not counting the tankers’ own emissions, released about a thousand metric tons of greenhouse gases into the atmosphere. It killed roughly eighty suspected combatants. The carbon cost per targeted individual was, in the strict arithmetic sense, absurd.

Why the numbers stay invisible

Given how striking the figures are, the obvious question is why the Pentagon’s fuel consumption isn’t a routine feature of climate policy debates. The answer, according to CNBC’s June 2019 reporting on the Crawford study, is essentially procedural. The Pentagon hasn’t consistently reported its fuel consumption to Congress in its budget submissions, so researchers have to piece the figures together from Department of Energy data and Defense Logistics Agency purchase records. When the 1997 Kyoto Protocol was negotiated, the United States successfully lobbied for military emissions to be exempted from national reporting requirements. When Kyoto was superseded by the 2015 Paris Agreement, military emissions were made optional to report rather than mandatory, which in practice means most countries don’t.

Where the Pentagon would rank

When Crawford applied standard emissions coefficients to the Pentagon’s actual fuel consumption, the 2017 total came out at approximately 59 million metric tons of carbon dioxide equivalent. That figure, if the Pentagon were counted as its own separate country, would have made it the world’s 55th largest greenhouse-gas emitter that year. Portugal, at roughly 51 million metric tons of national emissions, was ranked 57th on the Global Carbon Atlas. Sweden, at closer to 42 million metric tons, was ranked 65th. A single institution within a single country was generating more annual greenhouse gases than the total national output of several respectably-industrialised European nations. And nobody was including that figure in the calculations of what “the United States” was contributing to the climate crisis, because the international frameworks didn’t require it to be counted.

The war on terror in carbon terms

The picture across the wider historical span is even more striking. Between 2001, when the US invasion of Afghanistan formally began the post-9/11 military engagements, and 2017, the Pentagon emitted 1.2 billion metric tons of greenhouse gases. More than 400 million metric tons of that total was directly attributable to war-related fuel consumption, meaning fuel burned specifically in the course of prosecuting the wars in Iraq and Afghanistan and their various associated campaigns. The environmental cost of the American post-9/11 military engagements, measured purely in atmospheric carbon terms and setting aside every other consequence, was equivalent to running an additional mid-sized industrialised country flat-out for the entire two-decade period, quietly, off-books, uncounted by the international frameworks that treat every other source of emissions as measurable and reportable.