On the ground, “more than 50,000 children have reportedly been killed or injured since October 2023” in Gaza alone, UNICEF lamented last month. In Ukraine, more than 42,000 civilians have been killed or wounded, the UN Human Rights Commission reported. Countless more people are threatened by this week’s air strikes between Israel and Iran, not to mention last month’s hostilities between India and Pakistan.

Brave journalists on the ground risk their lives to tell the outside world what’s happening in these war zones. Less common is to tell the world what modern wars do to the sky—not only the sky over the war zones but the sky all people everywhere share.

Scientific analyses have consistently concluded that military operations in general—transporting troops, testing weapons, maintaining bases (the United States has more than 700 worldwide)—and modern war in particular are the most carbon-intensive activities on Earth. The gargantuan amounts of oil and other fossil fuels used to fly planes, launch missiles, drive tanks, propel ships, and power supply vehicles emit staggering amounts of planet-warming carbon dioxide.

That’s partly because the fuel efficiency of most war equipment is vanishingly small. “We’re talking gallons per mile, not miles per gallon,” Neta C. Crawford, a professor at the University of Oxford and author of The Pentagon, Climate Change, and War, told a Covering Climate Now press briefing last year. Emissions also spike when adversaries attack one another’s fossil-fuel infrastructure, as Israel, Iran, Russia, and Ukraine have reportedly done.

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Routine military operations—separate from war fighting—account for an estimated 5.5 percent of the world’s annual CO₂ emissions. “If the world’s militaries were a country, this figure would represent the fourth largest national carbon footprint in the world—higher than Russia,” Nina Lakhani reported in The Guardian. The 5.5 percent figure is only an estimate, Crawford told Lakhani, because a loophole the United States inserted into the Kyoto Protocol in 1997 exempts all militaries from disclosing their emissions—meaning the world’s total emissions are significantly higher than officially recognized.

A growing body of research by independent scholars is filling in the blanks, enabling journalists to report war’s long-term climate costs as well as its immediate human costs.

“The carbon footprint of the first 15 months of Israel’s war on Gaza will be greater than the annual planet-warming emissions of a hundred individual countries,” Lakhani wrote, summarizing one recent study. A separate study found that the war in Ukraine has a carbon footprint seven times larger—230 million tons of CO₂ equivalent, Manuel Planelles reported in El País, just short of the 270 million tons that all of Spain emitted in 2023.

As casualties continue to mount, journalists unfortunately will have plenty of opportunities to make the climate connection to the wars in Ukraine and the Middle East. Meanwhile, climate-driven weather disasters are growing more frequent and severe around the world even as some governments are boosting military spending. “Emissions go up in step with military spending,” Crawford notes, “and this is exactly the wrong time to be doing this.”