The U.S. oil and gas industry emits 13 million metric tons of the potent greenhouse gas methane from its operations each year, 60 percent more than estimated by the U.S. Environmental Protection Agency, according to a new study published in the journal Science.

Significantly, researchers found most of the emissions came from leaks, equipment malfunctions and other "abnormal" operating conditions. The climate impact of these leaks in 2015 was roughly the same as the climate impact of carbon dioxide emissions from all all U.S. coal-fired power plants operating in 2015, they found.

The new paper assessed measurements made at more than 400 well pads in six oil and gas production basins and scores of midstream facilities; measurements from valves, tanks and other equipment; and aerial surveys covering large swaths of the U.S. oil and gas infrastructure. The research was organized by the Environmental Defense Fund and drew on science experts from 16 research institutions including the University of Colorado Boulder and the University of Texas Austin.

Methane, the main ingredient of natural gas, is a potent greenhouse gas that has more than 80 times the warming impact of carbon dioxide over the first 20 years after its release. The new study estimates total US emissions at 2.3 percent of production, enough to erode the potential climate benefit of switching from coal to natural gas over the past 20 years. The methane lost to leakage is worth an estimated $2 billion, according to the Environmental Defense Fund, enough to heat 10 million homes in the U.S.