If the U.S. military were a nation state, it would be the world's 47th largest emitter of planet-warming greenhouse gases, a 2019 study found.

Though the British universities of Lancaster and Durham took account only of emissions from fuel usage in their study, it pointed to the huge impact that armed forces across the globe are having on the earth's climate.

Facing a battle against global warming, NATO has for the first time made it a central focus of planning and strategy.