Natural Gas from Shale Contributes to Global Warming

http://www.sciencedaily.com/releases/2011/04/110412065948.htm

ScienceDaily (Apr. 13, 2011) — Natural gas extracted from shale formations has a greater greenhouse gas footprint -- in the form of methane emissions -- than conventional gas, oil and coal over a 20 year period. This calls into question the logic of its use as a climate-friendly alternative to fossil fuels, according to Robert Howarth and colleagues, from Cornell University in New York.

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They calculated that, overall, during the life cycle of an average shale-gas well, between four to eight percent of the total production of the well is emitted to the atmosphere as methane, via routine venting and equipment leaks, as well as with flow-back return fluids during drill out following the fracturing of the shale formations. Routine production and downstream methane emissions are also large, but comparable to those of conventional gas.

Methane is a far more potent greenhouse gas than carbon dioxide, but methane also has a 10-fold shorter residence time in the atmosphere. As a result, its effect on global warming falls more rapidly. Methane dominates the greenhouse gas footprint for shale gas on a 20 year horizon, contributing up to three times more than does direct carbon dioxide emission. At this time scale, the footprint for shale gas is at least 20 percent greater than that for coal, and perhaps twice as great.

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