A team of scientists claim that both the U.S. EPA and the Europe-based Emission Database for Global Atmospheric Research (EDGAR) have vastly underestimated the amount of methane released to the atmosphere annually in the U.S.  Combining what they describe as “comprehensive atmospheric methane observations, extensive spatial datasets, and a high-resolution atmospheric transport model,” the researchers assessed methane emissions “across North America” in 2007 and 2008.

An article on the work was published in the November 26, 2013, Proceedings of the National Academy of Sciences of the United States of America.  The 15 individuals credited with authorship are affiliated with Harvard University, Carnegie Institution for Science, the University of Michigan, the National Oceanic and Atmospheric Administration, the University of Colorado, and the European Commission Joint Research Centre, among other institutions.

20 times stronger than CO2

In the U.S, methane is the second most prevalent GHG emitted from human activities.  Methane's lifetime in the atmosphere is much shorter than CO2, but methane is more efficient at trapping radiation than CO2.  Pound for pound, the comparative impact of methane on climate change is over 20 times greater than CO2 over a 100-year period.  According to the EPA, in 2011, methane accounted for about 9 percent of all U.S. GHG from human activities, primarily agriculture and natural gas and petroleum development.  The paper indicates that this percentage is nowhere near where it should be.

South-Central U.S.

Standing out among the results reported in the Proceedings were methane emissions in the South-Central U.S., which, the researchers say, were 2.7 times greater than those reported in most inventories.  For this region, the team found that much of the discrepancy was based in government underestimates of methane emissions from oil and gas drilling and processing.  The South-Central region includes states such as Texas, Oklahoma, Colorado, and Louisiana, where oil and gas activities are prominent.

Fossil fuel extraction and refining generate about 45 percent of methane emissions in that region, the scientists report, almost five times more than that the EDGAR estimate and about 24 percent of national methane emissions.  
Results indicate that emissions due to ruminants and manure are up to twice the magnitude of existing inventories, the researchers add. 

 “Successful regulation of greenhouse gas emissions requires knowledge of current methane emissions sources,” say the researchers.  “These results cast doubt on the U.S. EPA’s recent decision to downscale its estimate of national natural gas emissions by 25-30 percent.”