The U.S. oil and gas industry emits 13 million metric tons of methane from its operations each year – nearly 60 percent more than current estimates and enough to offset much of the climate benefits of burning natural gas instead of coal, according to a study published Thursday in the journal Science.

The higher volumes of natural gas leaking from across the industry’s supply chain would be enough to fuel 10 million homes and would be worth an estimated $2 billion, the researchers said.

The study, led by Environmental Defense Fund researchers and including 19 co-authors from 15 institutions, estimated that the current leak rate from U.S. oil and gas operations is 2.3 percent, significantly higher than the Environmental Protection Agency’s current estimate of 1.4 percent.

While the percentages seem small, methane is a potent greenhouse gas and the additional emissions would erase the climate advantages of burning natural gas instead of coal during the period when methane’s effects on the climate are most pronounced.

Though half of methane vanishes in 8.3 years, the EDF says it is still 84 times as powerful as carbon dioxide over 20 years. The EPA uses a broader time frame and says methane’s global warming effect is 28 to 36 times that of carbon dioxide over the course of a century.

“Natural gas losses are a waste of a limited natural resource, increase global levels of surface ozone pollution, and significantly erode the potential climate benefits of natural gas use,” the study’s authors wrote.

They added that the climate effects of emitting 13 million metric tons of methane over 20 years “roughly equals” the carbon dioxide emissions from all U.S. coal-fired power plants operating in 2015. It would equal about 31 percent of the carbon dioxide emissions from U.S. coal plants over a 100-year time horizon.

“In the short term, the climate impacts of burning coal in a modern plant vs. natural gas in a modern plant are similar as a result of the supply chain methane emissions,” Fred Krupp, president of the Environmental Defense Fund, said in an email. But, he added, “over the long term the climate impacts of using gas to generate electricity will be significantly less than those of using coal even with high methane emissions.”

Moreover, he added, “if methane emissions were reduced, which they can be easily, it could deliver significant short-term climate benefits as well.”

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