Long‐Term Measurements Show Little Evidence for Large Increases in Total U.S. Methane Emissions over the Past Decade

Author(s): Lan, Xin; Tans, Pieter; Sweeney, Colm; Andrews, Arlyn; Dlugokencky, Edward; Schwietzke, Stefan; Kofler, Jonathan; McKain, Kathryn; Thoning, Kirk; Crotwell, Molly; Montzka, Stephen; Miller, Benjamin R; Biraud, Sebastien C | Abstract: ©2019. The Authors. Recent studies show conflicting estimates of trends in methane (CH4) emissions from oil and natural gas (ONG) operations in the United States. We analyze atmospheric CH4 measurements from 20 North American sites in the National Oceanic and Atmospheric Administration 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 approximately 3.4 ± 1.4 %/year 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 U.S. 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.