U.S. Methane Emissions Higher Than Estimated

Estimates of how much methane is emitted to the atmosphere from the U.S. are too low, according to a new analysis of what’s actually in the air (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1314392110). Emissions inventories by agencies such as EPA are done with a “bottom up” approach that calculates emissions based on estimates of the amount of methane typically released from sources such as livestock and natural gas extraction. In the new work, a team led by Scot M. Miller and Steven C. Wofsy of Harvard University analyzed methane measurements made at ground level, on towers, and from aircraft in various locations across the U.S. in 2007 and 2008. They then used air transport models to track back from the measurement location to emission points. They found that methane emissions are generally 50% higher than EPA estimates, with livestock across the entire U.S. and fossil-fuel extraction in the South Central region as primary targets of underestimation.