Comment on acp-2021-671
Abstract
Abstract. We quantify methane emissions and their 2010–2017 trends by sector in the contiguous United States (CONUS), Canada, and Mexico by inverse analysis of in situ (GLOBALVIEWplus CH4 ObsPack) and satellite (GOSAT) atmospheric methane observations. The inversion uses as a prior estimate the national anthropogenic emission inventories for the three countries reported by the US Environmental Protection Agency (EPA), Environment and Climate Change Canada (ECCC), and the Instituto Nacional de Ecología y Cambio Climático (INECC) in Mexico to the United Nations Framework Convention on Climate Change (UNFCCC) and thus serves as an evaluation of these inventories in terms of their magnitudes and trends. Emissions are optimized with a Gaussian mixture model (GMM) at 0.5∘×0.625∘ resolution and for individual years. Optimization is done analytically using lognormal error forms. This yields closed-form statistics of error covariances and information content on the posterior (optimized) estimates, allows better representation of the high tail of the emission distribution, and enables construction of a large ensemble of inverse solutions using different observations and assumptions. We find that GOSAT and in situ observations are largely consistent and complementary in the optimization of methane emissions for North America. Mean 2010–2017 anthropogenic emissions from our base GOSAT + in situ inversion, with ranges from the inversion ensemble, are 36.9 (32.5–37.8) Tg a−1 for CONUS, 5.3 (3.6–5.7) Tg a−1 for Canada, and 6.0 (4.7–6.1) Tg a−1 for Mexico. These are higher than the most recent reported national inventories of 26.0 Tg a−1 for the US (EPA), 4.0 Tg a−1 for Canada (ECCC), and 5.0 Tg a−1 for Mexico (INECC). The correction in all three countries is largely driven by a factor of 2 underestimate in emissions from the oil sector with major contributions from the south-central US, western Canada, and southeastern Mexico. Total CONUS anthropogenic emissions in our inversion peak in 2014, in contrast to the EPA report of a steady decreasing trend over 2010–2017. This reflects offsetting effects of increasing emissions from the oil and landfill sectors, decreasing emissions from the gas sector, and flat emissions from the livestock and coal sectors. We find decreasing trends in Canadian and Mexican anthropogenic methane emissions over the 2010–2017 period, mainly driven by oil and gas emissions. Our best estimates of mean 2010–2017 wetland emissions are 8.4 (6.4–10.6) Tg a−1 for CONUS, 9.9 (7.8–12.0) Tg a−1 for Canada, and 0.6 (0.4–0.6) Tg a−1 for Mexico. Wetland emissions in CONUS show an increasing trend of +2.6 (+1.7 to +3.8)% a−1 over 2010–2017 correlated with precipitation.
Authors 22
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Harvard University · Sun Yat-sen University
Affiliation as printed
Guangdong Provincial Observation and Research Station for Climate Environment and Air Quality Change in the Pearl River Estuary, Zhuhai, Guangdong Province, China
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong Province, China
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Affiliation as printed
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
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Affiliation as printed
School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong Province, China
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Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research, Utrecht, the Netherlands
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Harvard University · Westlake University
Affiliation as printed
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
Institute of Advanced Technology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang Province, China
School of Engineering, Westlake University, Hangzhou, Zhejiang Province, China
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Affiliation as printed
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
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Affiliation as printed
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
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Affiliation as printed
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
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Affiliation as printed
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
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Affiliation as printed
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
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California Institute of Technology · Jet Propulsion Laboratory
Affiliation as printed
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
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California Institute of Technology · Jet Propulsion Laboratory
Affiliation as printed
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
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California Institute of Technology · Jet Propulsion Laboratory
Affiliation as printed
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
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Affiliation as printed
School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong Province, China
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University of Leicester · National Centre for Earth Observation
Affiliation as printed
Earth Observation Science, Department of Physics and Astronomy, University of Leicester, Leicester, UK
National Centre for Earth Observation, University of Leicester, Leicester, UK
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University of Leicester · National Centre for Earth Observation
Affiliation as printed
Earth Observation Science, Department of Physics and Astronomy, University of Leicester, Leicester, UK
National Centre for Earth Observation, University of Leicester, Leicester, UK
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Affiliation as printed
Environmental Defense Fund, Washington, DC, USA
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Affiliation as printed
RMI, New York, NY, USA
Watson Institute for International and Public Affairs, Brown University, Providence, RI, USA
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Environment and Climate Change Canada
Affiliation as printed
Environment and Climate Change Canada, Toronto, ON, Canada
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Affiliation as printed
RMI, Boulder, CO, USA
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Instituto Nacional de Ecología y Cambio Climático
Affiliation as printed
Instituto Nacional de Ecología y Cambio Climático (INECC), Mexico City, Mexico
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National Oceanic and Atmospheric Administration · NOAA Earth System Research Laboratory
Affiliation as printed
National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Boulder, CO, USA
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