As the world's largest oil consumer, the Defense Department is “the single largest producer of greenhouse gases in the world,” according to a 2019 study published by Brown University’s Watson Institute. Brown estimates the U.S. military’s carbon dioxide emissions at 59 million metric tons in 2017, comparable to the entire CO2 emissions of a small European country such as Portugal (59.8 million metric tons) or Austria (64.2 million metric tons).
The military’s emissions equate to just over 1% of overall U.S. carbon emissions, which were calculated at 5,088 million tons in 2017.
The Defense Department “has begun to adapt its plans, operations and installations to deal with climate change,” the Brown study notes, arguing that if it moved faster to reduce its fossil fuel consumption it would reduce the risks of the “dire” climate threats it is most concerned about.