11/25/2013
Spatial Distribution of U.S. Anthropogenic Methane Sources
Summary
This study, jointly funded by the Department of Energy’s Atmospheric Radiation Measurement (ARM) and Terrestrial Ecosystem Science (TES) programs along with support from the National Science Foundation and National Aeronautics and Space Administration, sought to quantitatively estimate 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. Using eddy covariance tower and aircraft-based atmospheric observations of methane, along with a high-resolution atmospheric transport model (STILT), results were compared to inventories from the U.S. Environmental Protection Agency and Emissions Database for Global Atmospheric Research (EDGAR) database. Current inventories from the database underestimate methane emissions nationally by a factor of ~1.5 to ~1.7. This study indicates that emissions due to ruminant animals (livestock) and manure are up to twice the magnitude of existing inventories. The discrepancy in methane source estimates is particularly pronounced in the south-central United States, where total emissions are ~2.7 times greater than in most inventories and account for ~24% of national emissions. The spatial patterns of emission fluxes and observed methane-propane correlations indicate that fossil fuel extraction and refining are major contributors (~45%) in the south-central United States. This result suggests that regional methane emissions due to fossil fuel extraction and processing could be nearly five times larger than in EDGAR, the most comprehensive global methane inventory. These results cast doubt on a recent decision to downscale estimates of national natural gas emissions by 25-30%. Overall, the investigators conclude that methane emissions associated with both the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories.
References
Miller, S. M., S. C. Wofsy, A. M. Michalak, E. A. Kort, A. E. Andrews, S. C. Biraud, E. J. Dlugokencky, J. Eluszkiewiczf, M. L. Fischer, G. Janssens-Maenhout, B. R. Miller, J. B. Miller, S. A. Montzkad, T. Nehrkornf, and C. Sweeney. 2013. “Anthropogenic Emissions of Methane in the United States,” Proceedings of the National Academy of Sciences (USA) 110(50), 20018-22. DOI:10.1073/pnas.1314392110.