Abstract
Abstract. We use 2010–2015 Greenhouse Gases Observing Satellite (GOSAT) observations of atmospheric methane columns over North America in a high-resolution inversion of methane emissions, including contributions from different sectors and their trends over the period. The inversion involves an analytical solution to the Bayesian optimization problem for a Gaussian mixture model (GMM) of the emission field with up to 0.5∘×0.625∘ resolution in concentrated source regions. The analytical solution provides a closed-form characterization of the information content from the inversion and facilitates the construction of a large ensemble of solutions exploring the effect of different uncertainties and assumptions in the inverse analysis. Prior estimates for the inversion include a gridded version of the Environmental Protection Agency (EPA) Inventory of US Greenhouse Gas Emissions and Sinks (GHGI) and the WetCHARTs model ensemble for wetlands. Our best estimate for mean 2010–2015 US anthropogenic emissions is 30.6 (range: 29.4–31.3) Tg a−1, slightly higher than the gridded EPA inventory (28.7 (26.4–36.2) Tg a−1). The main discrepancy is for the oil and gas production sectors, where we find higher emissions than the GHGI by 35 % and 22 %, respectively. The most recent version of the EPA GHGI revises downward its estimate of emissions from oil production, and we find that these are lower than our estimate by a factor of 2. Our best estimate of US wetland emissions is 10.2 (5.6–11.1) Tg a−1, on the low end of the prior WetCHARTs inventory uncertainty range (14.2 (3.3–32.4) Tg a−1), which calls for better understanding of these emissions. We find an increasing trend in US anthropogenic emissions over 2010–2015 of 0.4 % a−1, lower than previous GOSAT-based estimates but opposite to the decrease reported by the EPA GHGI. Most of this increase appears driven by unconventional oil and gas production in the eastern US. We also find that oil and gas production emissions in Mexico are higher than in the nationally reported inventory, though there is evidence for a 2010–2015 decrease in emissions from offshore oil production.
Highlights
Methane is the second-most important greenhouse gas in terms of radiative forcing (Stocker et al, 2013)
We find an increasing trend in US anthropogenic emissions over 2010–2015 of 0.4 % a−1, lower than previous Gases Observing Satellite (GOSAT)-based estimates but opposite to the decrease reported by the Environmental Protection Agency (EPA) Greenhouse Gas Emissions and Sinks (GHGI)
Major emission source sectors include wetlands, livestock, the fossil fuel industry, and waste management (Kirschke et al, 2013; Saunois et al, 2020). Individual countries report their anthropogenic emissions to the United Nations Framework Convention on Climate Change (UNFCCC) using methods prescribed by the Intergovernmental Panel on Climate Change (IPCC) (United Nations, 1992; IPCC, 2006)
Summary
Methane is the second-most important greenhouse gas in terms of radiative forcing (Stocker et al, 2013). Major emission source sectors include wetlands (the main natural source), livestock, the fossil fuel industry, and waste management (Kirschke et al, 2013; Saunois et al, 2020). Individual countries report their anthropogenic emissions to the United Nations Framework Convention on Climate Change (UNFCCC) using methods prescribed by the Intergovernmental Panel on Climate Change (IPCC) (United Nations, 1992; IPCC, 2006). We evaluate 2010–2015 North American emissions by inversion of data from the Greenhouse Gases Observing Satellite (GOSAT), which measures methane concentrations at high precision by solar backscatter in the shortwave infrared (SWIR) (Butz et al, 2011; Buchwitz et al, 2015; Kuze et al, 2016). We take the gridded version of the EPA GHGI (Maasakkers et al, 2016) as a prior estimate for the inversion, enabling us to use the inversion results to evaluate the GHGI and guide improvements in its representation of emission processes
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