Anthropogenic emissions of methane in the United States - PubMed (original) (raw)

. 2013 Dec 10;110(50):20018-22.

doi: 10.1073/pnas.1314392110. Epub 2013 Nov 25.

Steven C Wofsy, Anna M Michalak, Eric A Kort, Arlyn E Andrews, Sebastien C Biraud, Edward J Dlugokencky, Janusz Eluszkiewicz, Marc L Fischer, Greet Janssens-Maenhout, Ben R Miller, John B Miller, Stephen A Montzka, Thomas Nehrkorn, Colm Sweeney

Affiliations

Anthropogenic emissions of methane in the United States

Scot M Miller et al. Proc Natl Acad Sci U S A. 2013.

Abstract

This study quantitatively estimates the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial datasets, and a high-resolution atmospheric transport model. Results show that current inventories from the US Environmental Protection Agency (EPA) and the Emissions Database for Global Atmospheric Research underestimate methane emissions nationally by a factor of ∼1.5 and ∼1.7, respectively. Our study indicates that emissions due to ruminants and manure are up to twice the magnitude of existing inventories. In addition, the discrepancy in methane source estimates is particularly pronounced in the south-central United States, where we find total emissions are ∼2.7 times greater than in most inventories and account for 24 ± 3% of national emissions. The spatial patterns of our emission fluxes and observed methane-propane correlations indicate that fossil fuel extraction and refining are major contributors (45 ± 13%) in the south-central United States. This result suggests that regional methane emissions due to fossil fuel extraction and processing could be 4.9 ± 2.6 times larger than in EDGAR, the most comprehensive global methane inventory. These results cast doubt on the US EPA's recent decision to downscale its estimate of national natural gas emissions by 25-30%. Overall, we conclude that methane emissions associated with both the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories.

Keywords: climate change policy; geostatistical inverse modeling.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

US anthropogenic methane budgets from this study, from previous top-down estimates, and from existing emissions inventories. The south-central United States includes Texas, Oklahoma, and Kansas. US EPA estimates only national, not regional, emissions budgets. Furthermore, national budget estimates from EDGAR, EPA, and Kort et al. (13) include Alaska and Hawaii whereas this study does not.

Fig. 2.

Fig. 2.

CH4 concentration measurements from 2007 and 2008 and the number of observations associated with each measurement type. Blue text lists the number of observations associated with each stationary tower measurement site.

Fig. 3.

Fig. 3.

The 2-y averaged CH4 emissions estimated in this study (A) compared against the commonly used EDGAR 4.2 inventory (B and C). Emissions estimated in this study are greater than in EDGAR 4.2, especially near Texas and California.

Fig. 4.

Fig. 4.

A model–measurement comparison at several regular NOAA/DOE aircraft monitoring sites (averaged over 2007–2008). Plots include the measurements; the modeled boundary condition; the summed boundary condition and wetland contribution (from the Kaplan model); and the summed boundary, wetland, and anthropogenic contributions (from EDGAR v4.2 and the posterior emissions estimate).

Fig. 5.

Fig. 5.

Correlations between propane and CH4 at NOAA/DOE aircraft observation sites in Oklahoma (A) and Texas (B) over 2007–2012. Correlations are higher in these locations than at any other North American sites, indicating large contributions of fossil fuel extraction and processing to CH4 emitted in this region.

Comment in

References

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