A study published Friday in the journal Science says the Environmental Protection Agency and other organizations have underestimated natural gas emissions in the country.
“Atmospheric tests covering the entire country indicate emissions around 50 percent more than the EPA estimates. And that’s a moderate estimate,” lead author and Stanford University professor Adam Brandt said in a news release from the researchers.
The study was written by researchers at several U.S. universities and the Energy Department’s National Renewable Energy Laboratory. Emissions of methane, the principal component of natural gas, are important because the gas has a powerful greenhouse effect — about 30 times more than the same amount of carbon dioxide, the study said.
The EPA has estimated that about 1.5 percent of the nation’s gross production of methane leaks into the atmosphere.
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Among the study’s sometimes surprising findings:
• Generating electricity by burning gas rather than coal reduces the total greenhouse effect over 100 years. Some researchers have long contested that gain, but the study said the natural gas system would have to leak 7.4 percent of total production, which it called unlikely, to match coal’s climate impact.
• Replacing big diesel engines on over-the-road truck and bus fleets “probably makes the globe warmer, because diesel engines are relatively clean” and it’s “improbable” that the entire natural gas system could reduce leakage below the 1.7 percent needed to beat diesel. “Fueling trucks and buses with natural gas may help local air quality and reduce oil imports, but it is not likely to reduce greenhouse gas emissions,” Brandt said.
• Replacing gasoline in passenger cars with natural gas “is probably borderline in terms of climate,” Brandt said. That “switching point” would be at a leakage rate of 3.8 percent, the study said.
Unlike previous studies that have tried to measure or estimate emissions from specific activities, this study “does not try to attribute percentages of the excess emissions to natural gas, oil, coal, agriculture, landfills, etc., because emissions rates for most sources are so uncertain.” Researchers instead measured methane concentrations in the atmosphere around the nation and compared them with expected results based on about 200 previous studies.
Addressing “some recent studies showing very high methane emissions in regions with considerable natural gas infrastructure,” the authors concluded that those results “are not representative of the entire gas system.”
The news release didn’t say which studies the group was referring to. But in 2012, researchers in Colorado estimated that producers in the Denver-Julesburg Basin were losing 4 percent of their gas. Another 2013 study based on a one-day flight over Utah’s Uintah Basin estimated leakage at 6 to 12 percent of total production.
The study was funded by a grant from the Cynthia and George Mitchell Foundation through a grant to Novim, a not-for-profit formed in 2007 by scientists and engineers at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara.