NOAA study finds little evidence for large increases in total US methane emissions over the past decade
A study by a team of researchers from the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory has found that methane emissions from oil and natural gas production in the United States may not be rising as quickly as had been feared.
Methane is a potent greenhouse gas emitted during the natural gas production cycle; the nearly 50% increase in natural gas production from 2006 to 2015 has led to concerns that emissions have risen pari passu. The NOAA team found that this is not the case and that, in fact, total methane emissions have remained essentially constant over that period.
They suggest that the overestimates of some recent studies are a function of a decreasing ratio of methane to ethane emissions. Their paper is published in the journal Geophysical Research Letters.
Trends in CH4, C3H8 and C2H6 enhancements (‘Δ’) over North America in recent years (2006-2015 for CH4, and 2008-2015 for C2H6 and C3H8 for most sites. Green squares and black dots show ONG and non-ONG sites, respectively. ‘-s’ following a site code indicates surface site. For all bar charts each tick increment is 2% yr-1 and the horizontal axis crosses at 0% yr-1 (e.g. ETL and DND); ‘% yr-1’ means increase of Δ relative to previous year. Error bars show 1σ uncertainty. For CH4 and C3H8, enhancements are relative to mid-troposphere measurements. Lan et al.
Recent studies show conflicting estimates of trends in methane (CH4) emissions from oil and natural gas (ONG) operations in the US. We analyze atmospheric CH4 measurements from 20 North American sites in the NOAA Global Greenhouse Gas Reference Network and determined trends for 2006‐2015.
Using CH4 vertical gradients as an indicator of regional surface emissions, we find no significant increase in emissions at most sites and modest increases at three sites heavily influenced by ONG activities.
Our estimated increases in North American ONG CH4 emissions (on average ~ 3.4 ± 1.4 % yr‐1 for 2006‐2015, ±σ) are much smaller than estimates from some previous studies and below our detection threshold for total emissions increases at the east coast sites that are sensitive to US outflows. We also find an increasing trend in ethane/methane emission ratios which has resulted in major overestimation of oil and gas emissions trends in some previous studies.—Lan et al.
Lan, X., Tans, P., Sweeney, C., Andrews, A., Dlugokencky, E., Schwietzke, S., et al ( 2019). “Long‐Term Measurements Show Little Evidence for Large Increases in Total U.S. Methane Emissions over the Past Decade.” Geophysical Research Letters, 46 doi: 10.1029/2018GL081731