The paper, "Anthropogenic emissions of methane in the United States", written by 15 climate scientists was published Nov. 25 in the Proceedings of the National Academy of Sciences (PNAS). "Its conclusions are sharply at odds with the two most comprehensive estimates of methane emissions, by the Environmental Protection Agency (EPA) and an alliance of the Netherlands and the European Commission," writes Michael Wines.
According to the EPA's "Overview of Greenhouse Gases" webpage on methane emissions:
Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities [after carbon dioxide which accounts for 84%]. In 2011, CH4 accounted for about 9% of all U.S. greenhouse gas emissions from human activities... Pound for pound, the comparative impact of CH4 on climate change is over 20 times greater than CO2 over a 100-year period. [See 'overview' for the other three gases]
The most serious differences occurred where oil and gas drilling was concentrated. "Methane discharges in Texas and Oklahoma were 2.7 times greater than conventional estimates. Emissions from oil and gas activity alone could be five times greater than the prevailing estimate, the report said."
The E.P.A. has stated that all emissions of methane, from both man-made and natural sources, have been slowly but steadily declining since the mid-1990s. In April, the agency reduced its estimate of methane discharges from 1990 through 2010 by 8 to 12 percent, largely citing sharp decreases in discharges from gas production and transmission, landfills and coal mines.
The new analysis calls that reduction into question, saying that two sources of methane emissions in particular — from oil and gas production and from cattle and other livestock — appear to have been markedly larger than the E.P.A. estimated during 2007 and 2008.
In September, Michael Wine had written about a University of Texas-Austin study, also published in PNAS, but unlike this recent study, it was not based on estimates but actual methane released from fracking operations. It concluded that "it was probably less than the Environmental Protection Agency estimated in 2011."
"This new work clearly points to the importance of the E.P.A. updating how it tracks this important emission, and also bolsters arguments for the Obama administration to move forward faster with its proposed standard [PDF] for cutting leaks and emissions from oil and gas operations," writes Andrew Revkin in The New York Times DoT Earth blog.
