Robert W. Howarth, Renee Santoro, and Anthony Ingraffea (forthcoming in Climatic Change)
Cornell University researchers say that natural gas pried from shale formations is dirtier than coal in the short term, rather than cleaner, and “comparable” in the long term…states a pre-publication copy of the study, which is slated to be published in the journal Climatic Science and originally obtained by The Hill newspaper.
That finding — fiercely disputed by the gas industry — undermines the widely stated belief that gas is twice as “clean” as coal in terms of greenhouse gas emissions. [From Greenwire article by Mike Soraghan, sub. req'd]
[Abstract] We evaluate the greenhouse gas footprint of natural gas obtained by high-volume 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 life-time 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.
Michael Levi’s take: http://blogs.cfr.org/levi/2011/04/15/some-thoughts-on-the-howarth-shale-gas-paper/
RealClimate post on this paper: http://www.realclimate.org/index.php/archives/2011/04/fracking-methane/