New Study Indicates U.S. Methane Emissions Overestimated

A recent research study has shown methane emissions are up to 10 times lower than past studies had shown.  The report, sponsored by the National Oceanic and Atmospheric Administration (NOAA), involved researchers with the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder, NOAA Earth System Research Laboratory, and the Lawrence Berkeley National Laboratory.  

The past research used ethane as a tracer for oil and gas activity, with the assumption that the ratio of ethane to methane in natural gas production regions is constant.  Analysis in the current report shows that ethane-to-methane ratios are increasing, which means there have been major overestimations of oil and gas emission trends.  "What this means is if you want to track methane, you have to measure methane," said Xin Lan, lead author of the study, 'Long-term measurements show little evidence for large increases in total US methane emissions over the past decade'.

Atmospheric methane air samples collected from 20 sites, a part of NOAA's Global Greenhouse Gas Reference Network, were studied to analyze the various gas concentrations close to the ground, where emissions occur, and in the atmosphere where the influence of recent surface emissions are minimal.  "While we analyzed a decade's worth of data and while we do find some increase in methane downwind of oil and gas activity, we do not find a statistically significant trend in the US for the total methane emissions," explained Lan.

The study is one of the first to explore trends in methane data from sites established by the 2004 North American Carbon Program (NACP), a multi-agency, multidisciplinary scientific research program focused on carbon sources and sinks in North American and its adjacent oceans.   Arlyn Andrews, chief of the NOOA Global Monitoring Division Cycle Group, indicated the 20 sites across the country provide enough measurements to evaluate aggregate emissions at large regional scales.  "If we had more sampling sites, we would be able to provide more specificity about methane sources in regions dominated by agriculture and oil and gas," Andrews stated. 

The paper can be found in AGU publication, Geophysical Research Letters.