Sunday, October 23, 2011

Greenhouse Gas Emissions from Shale Gas

"Unconventional" shale gas obtained through hydraulic fracturing or fracking has been very controversial recently. Local residents have claimed that their water has been contaminated in areas of Pennsylvania by the activities of the gas companies. There has also been concern about earthquakes triggered by the process. It turns out according to Robert Howarth (brother of Rich Howarth, editor of Ecological Economics) et al. that due to heightened methane emissions, gas obtained in this way has a higher total warming potential in the short run (of several decades) than does using coal. This is despite the fact that when burnt gas emits around half the CO2 for each joule than does coal and gas combustion is on average more efficient in producing electricity - it is a higher quality fuel. I've long wondered about whether leakage of methane gas negated the benefit of reduced carbon dioxide from natural gas, which is one reason I researched the literature on global emissions of methane. It turns out that emissions from conventional gas production and distribution systems do not negate the greenhouse benefits of gas.* But emissions from fracking might.

* Wigley (2011) argues that in the short-run switching to conventional natural gas from coal increases global warming even without any methane leakage. This depends on the reduction in sulfate aerosols produced by burning coal, which cool the climate. But sulfate aerosols are being reduced anyway even if we stick with coal use. This is taken into account in Wigley's analysis - switching to gas though still results in a faster than BAU reduction in aerosols. OTOH even under a 10% leakage rate switching to gas reduces climate change relative to BAU after 2140.

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