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Physicians Scientists & Engineers for Healthy Energy
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Methane and the Greenhouse-Gas Footprint of Natural Gas from Shale Formations

Climatic Change Letters
14 Apr 2011 (04/14/2011)
Howarth RW, Santoro R, Ingraffea A.
Acknowledgments:
Preparation of this paper was supported by a grant from the Park Foundation and by an endowment fund of the David R. Atkinson Professorship in Ecology & Environmental Biology at Cornell University. We thank R. Alvarez, C. Arnold, P. Artaxo, A. Chambers, D. Farnham, P. Jamarillo, N. Mahowald, R. Marino, R. McCoy, J. Northrup, S. Porder, M. Robertson, B. Sell, D. Shrag, L. Spaeth, and D. Strahan for information, encouragement, advice, and feedback on our analysis and manuscript. We thank M. Hayn for assistance with the figures. Two anonymous reviewers and Michael Oppenheimer provided very useful comments on an earlier version of this paper.

Abstract

We evaluate the greenhouse gas footprint of natural gas obtained by highvolume hydraulic fracturing from shale formations, focusing on methane emissions. Natural gas is composed largely of methane, and 3.6% to 7.9% of the methane from shale-gas production escapes to the atmosphere in venting and leaks over the lifetime of a well. These methane emissions are at least 30% more than and perhaps more than twice as great as those from conventional gas. The higher emissions from shale gas occur at the time wells are hydraulically fractured - as methane escapes from flow-back return fluids - and during drill out following the fracturing. Methane is a powerful greenhouse gas, with a global warming potential that is far greater than that of carbon dioxide, particularly over the time horizon of the first few decades following emission.  Methane contributes substantially to the greenhouse gas footprint of shale gas on shorter time scales, dominating it on a 20-year time horizon. The footprint for shale gas is greater than that for conventional gas or oil when viewed on any time horizon, but particularly so over 20 years. Compared to coal, the footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years.


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Howarth R, Shindell D, Santoro R, Ingraffea A, Phillips N, Townsend-Small A (2012). Methane Emissions from Natural Gas Systems. Background Paper Prepared for the National Climate Assessment Reference number 2011-0003.


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