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Wednesday, November 27, 2013

U.S. methane emissions may be 50% more than EPA measure

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U.S. emissions of methane, a potent heat-trapping greenhouse gas, may be 50% higher than federal estimates, reports a team of Harvard and other researchers today.

Nationwide, emissions from cows and livestock operations may be twice as high as previously thought, and in the south-central region, those from fossil fuel extraction and refining may be almost five times higher than calculated by the U.S. Environmental Protection Agency, according to a study in the Proceedings of the National Academy of Sciences.

"It's really a very clear signal" of how much methane U.S. industry and other sources emit, says co-author Anna Michalak of the Carnegie Institution of Science's Department of Global Ecology. She says the study of the continental USA combines an unprecedented amount of data, taken by federal agencies from the tops of telecommunication towers, with newer statistical tools and meteorological models to calculate how much methane is actually in the atmosphere and where it probably came from.

This top-down approach is notably different from the EPA's bottom-up estimates, which calculate emissions based on the amount of methane typically released per cow or per unit of coal or natural gas sold.

"The main result is significant," says co-author Colm Sweeney of the University of Colorado-Boulder, who leads the aircraft group that does flyovers to measure methane for NOAA's Earth System Research Laboratory Global Monitoring System. Sweeney says it provides an overall...

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