(Bloomberg) -- The U.S. military is belching more global-warming pollutants than some industrialized nations, with about a third of its emissions occurring in major conflict zones such as Afghanistan and Iraq, according to a new study.

American armed forces -- with a globe-spanning array of bases, warships, planes and land vehicles -- are the world’s largest institutional emitter of greenhouse gases, topping countries including Sweden and Denmark, according to the study from Brown University’s Costs of War project. A spokesman for the Pentagon didn’t immediately return a request for comment.

The study estimated the carbon footprint of the many U.S. military operations since the Sept. 11, 2001, terrorist attacks. The results: 766 million metric tons of carbon dioxide equivalent released from 2001 through 2017. That includes 400 million tons emitted in major conflict zones. Add in facilities and other routine factors, and the total carbon footprint over those years rises to 1.2 billion tons.

For comparison, total global greenhouse emissions in 2017 -- including everything from power generation to changes in land use -- were 53.5 billion tons, according to the United Nations Environment Programme.

The U.S. doesn’t put a price on emissions. If it did, however, the Pentagon could face a steep bill. Greenhouse gas emission allowances sold in California’s cap-and-trade system, for example, cost $17.45 a ton. So the price for all of the military’s releases since 2001 through 2017 would come to $21.1 billion.

The latest report’s author -- Neta Crawford, a political science professor at Boston University and co-director of the Costs of War project -- previously gained notice for trying to estimate the price of post-Sept. 11 wars. Her estimate for that was $6 trillion, if Homeland Security and the costs of caring for veterans were included.

She acknowledges the Pentagon’s ongoing efforts to explore alternative energy technologies, from renewable fuels to solar power. But she also argues in her latest report that much more work needs to be done, saying cutting emissions could help stave off the worst effects of global warming and lessen conflicts that Pentagon planners have previously warned that climate change could provoke.

The effort could also have the benefit, she said, of cutting oil use and thereby decreasing the need for American forces in the Middle East, particularly the Persian Gulf. The report was issued one day before two oil tankers in the Gulf suffered damage from explosions, with one possibly struck by a torpedo.

To contact the reporter on this story: David R. Baker in San Francisco at dbaker116@bloomberg.net

To contact the editors responsible for this story: Lynn Doan at ldoan6@bloomberg.net, Pratish Narayanan, Steven Frank

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