We present a new data set of annual historical (1750 -2014) anthropogenic chemically reactive gases (CO, CH 4 , NH 3 , NO X , SO 2 , NMVOC), carbonaceous aerosols (BC and OC), and CO 2 developed with the 25Community Emissions Database System (CEDS). We improve upon existing inventories with a more consistent and reproducible methodology applied to all emissions species, updated emission factors, and recent estimates through 2014. The data system relies on existing energy consumption data sets and regional and country-specific inventories to produce trends over recent decades. All emissions species are consistently estimated using the same activity data over all time periods. Emissions are provided on an annual basis at the level of country and sector and gridded with 30 monthly seasonality. These estimates are comparable to, but generally slightly higher than, existing global inventories. Emissions over the most recent years are more uncertain, particularly in low-and middle-income regions where country-specific emission inventories are less available. Future work will involve refining and updating these emission estimates, estimating emissions uncertainty, and publication of the system as open source software. 35Geosci. Model Dev. Discuss.,

US natural gas production increased by ˜43% between 2005 and 2015, but there is disagreement in the scientific literature on whether this growth led to increased methane emissions. In this study, we evaluate the possible contributions of emissions versus meteorology to an upward trend in US atmospheric methane observations during 2007-2015. We find that interannual variability (IAV) in meteorology yields an apparent upward trend in atmospheric methane across much of the US. We further find that IAV in atmospheric methane at several observation sites is correlated with IAV in local wind speed. Overall, our results show that US trends in atmospheric methane largely reflect variability in meteorology, and are unlikely to be a direct reflection of trends in emissions. The results of this study therefore lend support for the conclusion that there was little upward trend in US methane emissions during this time.

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The US is one of the largest anthropogenic emitters of methane, behind only China and India (Saunois et al., 2020). Numerous recent studies indicate that US methane emissions are 48%-76% higher than estimated by the EPA Inventory of US Greenhouse Gas Emissions and Sinks (GHGI) (