Publication Date:
2017-03-09
Description:
Recent studies have proposed significant increases in CH 4 emissions possibly from oil and gas (O&G) production, especially for the US where O&G production has reached historically high levels over the past decade [ US EIA , 2016; Turner et al. , 2016; Hausmann et al. , 2015; Franco et al. , 2016]. In this study, we show that an ensemble of time-dependent atmospheric inversions constrained by calibrated atmospheric observations of surface CH 4 mole fraction, with some including space-based retrievals of column average CH 4 mole fractions, suggests that North American CH 4 emissions have been flat over years spanning 2000 through 2012. Estimates of emission trends using zonal gradients of column average CH 4 calculated relative to an upstream background are not easy to make due to atmospheric variability, relative insensitivity of column average CH 4 to surface emissions at regional scales, and fast zonal synoptic transport. In addition, any trends in continental enhancements of column average CH 4 are sensitive to how the upstream background is chosen, and model simulations imply that short-term (4 years or less) trends in column average CH 4 horizontal gradients of up to 1.5 ppb/yr can occur just from inter-annual transport variability acting on a strong latitudinal CH 4 gradient. Finally, trends in spatial gradients calculated from space-based column average CH 4 can be significantly biased (〉2-3 ppb/yr) due to the non-uniform and seasonally varying temporal coverage of satellite retrievals.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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