U.S. CH4 emissions from oil and gas production: Have recent large increases been detected?

Recent studies have proposed significant increases in CH₄ emissions possibly from oil and gas (O&G) production, especially for the U.S. where O&G production has reached historically high levels over the past decade. In this study, we show that an ensemble of time‐dependent atmospheric inversions constrained by calibrated atmospheric observations of surface CH₄ mole fraction, with some including space‐based retrievals of column average CH₄ mole fractions, suggests that North American CH₄ emissions have been flat over years spanning 2000 through 2012. Estimates of emission trends using zonal gradients of column average CH₄ calculated relative to an upstream background are not easy to make due to atmospheric variability, relative insensitivity of column average CH₄ to surface emissions at regional scales, and fast zonal synoptic transport. In addition, any trends in continental enhancements of column average CH₄ are sensitive to how the upstream background is chosen, and model simulations imply that short‐term (4 years or less) trends in column average CH₄ horizontal gradients of up to 1.5 ppb/yr can occur just from interannual transport variability acting on a strong latitudinal CH₄ gradient. Finally, trends in spatial gradients calculated from space‐based column average CH₄ can be significantly biased (>2–3 ppb/yr) due to the nonuniform and seasonally varying temporal coverage of satellite retrievals.