(CBS Local) — The United States military alone produces more planet-warming greenhouse gas emissions than many smaller industrialized countries such as Sweden and Portugal, according to a new study.

The Pentagon, which oversees the U.S. Department of Defense, released 59 million metric tons of carbon dioxide and other greenhouse gases in 2017, according to Brown University’s “Costs of War” project.

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If the Pentagon was a country, its emissions would make it the world’s 55th largest greenhouse gas emitter in the world, ahead of Portugal (which is ranked 57th) and Sweden (ranked 65th), said Neta Crawford, the study’s author and a political scientist at Boston University.

China is the world’s largest emitter of carbon dioxide, the main gas responsible for climate change, followed by the United States.

U.S. Navy variant of the F-35 Joint Strike Fighter conducts a test flight over the Chesapeake Bay. (Lockheed Martin via Getty Images)

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“Although the Pentagon has, in recent years, increasingly emphasized what it calls energy security — energy resilience and conservation — it is still a significant consumer of fossil fuel energy,” Crawford said.

The U.S. Department of Defense is the largest institutional consumer of fossil fuels in the world, the study said. Using and moving troops and weapons accounted for approximately 70% of its energy consumption, mostly due to the burning of jet and diesel fuel.

The report warned of serious consequences if the Pentagon does nothing to curb its use of fossil fuels.

“Absent any change in US military fuel use policy, the fuel consumption of the US military will necessarily continue to generate high levels of greenhouse gases,” the study said. “These greenhouse gases, combined with other U.S. emissions, will help guarantee the nightmare scenarios that the military predicts and that many climate scientists say are possible.”

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There has been no comment yet from the Pentagon.