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

Abstract

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.

MERLIN: A French-German Space Lidar Mission Dedicated to Atmospheric Methane

“…This is especially true for changes (inter-annual variations, trends, etc.) in regional to global emissions, which can generally be more safely inferred than total annual emissions because (at least) some systematic errors vanish when looking at the difference between two time periods (e.g., [16,83]). The success of MERLIN would open the possibility to develop, jointly with surface observations and passive missions providing CH4 imagery, inversion It makes use of the small fraction of emitted laser radiation which is reflected by a "hard" target (i.e., the Earth's surface or a cloud top) towards the instrument's receiver, and subsequently converted into electrical signals by a photodetector.…”

“…in regional to global emissions, which can generally be more safely inferred than total annual emissions because (at least) some systematic errors vanish when Remote Sens. 2017, 9, 1052 9 of 29 looking at the difference between two time periods (e.g., [16,83]). The success of MERLIN would open the possibility to develop, jointly with surface observations and passive missions providing CH 4 imagery, inversion frameworks for the monitoring of regional CH 4 emission changes with time.…”

2010–2015 methane trends over Canada, the United States, and Mexico observed by the GOSAT satellite: contributions from different source sectors

“…The US livestock emissions show a 3.6 ± 2.3% a Inverse analyses of methane concentrations in surface air measured as part of the North American Carbon Program (NACP; Wofsy and Harris, 2002) for 2010-2014 reveal no significant trends in US emissions over that period (Benmergui et al, 2015;Bruhwiler et al, 2017). We examined whether the trends inferred from this work are consistent with the information provided by NACP surface data.…”

“…Bruhwiler et al (2017) pointed out that large-scale meridional transport could alias trends in this background estimate onto trends in the emissions.…”

Designing the Climate Observing System of the Future

“…Understanding carbon fluxes on a continental scale is currently challenged by a lack of high-quality, detailed observations. Such an understanding could help identify regions of carbon uptake and regions where energy choices are having a positive impact (Bruhwiler et al, 2017). 7.…”