Methane emissions vastly surpass previous estimates

November 25, 2013

Washington, D.C.-- Government calculations of total U.S. methane emissions may underestimate the true values by 50 percent, a new study finds. The results are published the week of November 25 in the early online edition of the Proceedings of the National Academy of Sciences, and cast doubt on a recent Environmental Protection Agency decision to downscale its emissions estimate.

Carnegie's Anna Michalak, Harvard's Scot Miller and Steven Wofsy, and colleagues used atmospheric methane observations from across North America in 2007 and 2008 to improve estimates of methane gas emissions from a variety of human sources, including agriculture and fossil fuel drilling and refining.

The study found large discrepancies with government estimates in some regions of the United States, particularly the south-central US, where total methane emissions were 2.7 times greater than those reported in most inventories. Emissions from oil and gas drilling and processing in this region could account for 50% of that total, representing a source of methane almost five times higher than in the most commonly used global emissions database.

Methane is the second-most important greenhouse gas after carbon dioxide, and the study findings may help inform national and state greenhouse gas reduction strategies, according to the authors.

The team used modeling tools developed by Michalak's lab that make it possible to trace variations in atmospheric methane measurements back to emissions throughout the U.S., and to relate the emissions to known economic sectors. The methods thereby provide a direct constraint on total emissions, as well as provide insight into what is behind them.
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This work was supported by the American Meteorological Society Graduate Student Fellowship/Department of Energy (DOE) Atmospheric Radiation Measurement Program, a DOE Computational Science Graduate Fellowship, and the National Science Foundation Graduate Research Fellowship Program. NOAA measurements were funded in part by the Atmospheric Composition and Climate Program and the Carbon Cycle Program of NOAA's Climate Program Office. Support for this research was provided by NASA Grants NNX08AR47G and NNX11AG47G, NOAA Grants NA09OAR4310122 and NA11OAR4310158, National Science Foundaton (NSF) Grant ATM- 0628575, and Environmental Defense Fund Grant 0146-10100 (to Harvard University). Measurements at Walnut Grove were supported in part by a California Energy Commission Public Interest Environmental Research Program grant to Lawrence Berkeley National Laboratory through the US Department of Energy under Contract DE-AC02-05CH11231. DOE flights were supported by the Office of Biological and Environmental Research of the US Department of Energy under Contract DE-AC02-05CH11231 as part of the Atmospheric Radiation Measurement Program (ARM), ARM Aerial Facility, and Terrestrial Ecosystem Science Program. Weather Research and Forecasting-Stochastic Time-Inverted Lagrangian Transport model development at Atmospheric and Environmental Research has been funded by NSF Grant ATM-0836153, NASA, NOAA, and the US intelligence community.

The Department of Global Ecology was established in 2002 to help build the scientific foundations for a sustainable future. The department is located on the campus of Stanford University, but is an independent research organization funded by the Carnegie Institution. Its scientists conduct basic research on a wide range of large-scale environmental issues, including climate change, ocean acidification, biological invasions, and changes in biodiversity.

The Carnegie Institution for Science is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Carnegie Institution for Science

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