Ambiguity in Recent Changes to US Methane Emissions

US natural gas production has increased by ~46% from 18 to 26.6 trillion cubic feet per year between 2006 and 2016 with the technological breakthrough of combining horizontal drilling and hydraulic fracturing. Methane emissions from the oil and natural gas (O&G) industry are emitted into the atmosphere by leaks that occur during exploration, production, transmission, and distribution. With this recent gas production boom, however, estimates of trends in US atmospheric methane have been ambiguous and controversial. Two studies examined GOSAT observations and argue there has been a large increase (~30%) in US methane emissions (Turner et al. 2016, Sheng et al. 2018). Conversely, Lan et al. (2018) argued that many NOAA observation sites show no evidence for increasing US methane emissions and Maasakkers et al. (2020) estimated a similar 0.4% a-1 increasing trend in US emissions using GOSAT observations. In this study, we employ a combination of emissions modeling, atmospheric transport modeling, and atmospheric methane observations from in-situ and satellite platforms to evaluate the drivers of recent upward trends in atmospheric methane observations within the US. We design a controlled experiment with four modeling scenarios to examine the impact of (1) plausible trends in surface emissions and (2) inter-annual variability (IAV) in meteorology to methane trends in atmospheric observations. We find that IAV in meteorology yields an apparent upward trend in atmospheric methane across much of the United States and can explain recent trends in atmospheric observations. We also find that this meteorology-driven trend overshadows the atmospheric imprint of any plausible trends in surface emissions. Furthermore, we evaluate the relationship between methane enhancements and several meteorological factors at modeling locations to identify the possible meteorological cause of IAV. The results suggest IAV in local wind speed can explain IAV in atmospheric methane at many atmospheric observation sites.