Study Finds U.S. Methane Emissions Are Much Higher Than EPA Measure

December 27, 2013A new study shows that U.S. emissions of methane, a potent heat-trapping greenhouse gas, may be 50 percent higher than federal estimates, a team of Harvard and other researchers reported recently. The reason has a lot to do with methodology, as the study suggests that the EPA may not be including all methane sources. 

Nationwide, emissions from cows and livestock operations may be twice as high as previously thought. In the south-central region, those from fossil-fuel extraction and refining may be almost five times higher than calculated by the EPA, according to a study in the Proceedings of the National Academy of Sciences.
 
Co-author Anna Michalak, of the Carnegie Institution of Science's Department of Global Ecology, says the study of the continental U.S. 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 picture, quantifies the discrepancy between the two approaches and shows the need for more observation stations.
The discrepancy may be because the EPA is not measuring every possible source, such as broken natural gas pipes that are leaking methane, says co-author Steven Wofsy, an atmospheric and environmental professor at Harvard University's School of Engineering and Applied Science.
 
This top-down analysis echoes the overall findings of a study Wofsy did in 2006 but offers much finer detail that will be used to create a national methane database. Yet he says while it may indicate what role the natural gas industry plays, it can't distinguish whether emissions come from drilling, processing or refining.
 

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