CORNELL (US) — Methane-rich natural gas extracted from Marcellus shale has 105 times more global warming impact, pound for pound, than carbon dioxide.
While natural gas has been touted as a clean-burning fuel that produces less carbon dioxide than coal, there is concern about the methane leaking into the atmosphere during hydraulic fracturing.
Even small leaks make a big difference—as much as 8 percent of the methane in shale gas leaks into the air during the lifetime of a hydraulic shale gas well—up to twice what escapes from conventional gas production.
“The take-home message is that if you do an integration of 20 years following the development of the gas, shale gas is worse than conventional gas and is, in fact, worse than coal and worse than oil,” says Robert Howarth, professor of ecology and environmental biology at Cornell University.
“We are not advocating for more coal or oil, but rather to move to a truly green, renewable future as quickly as possible. We need to look at the true environmental consequences of shale gas.”
Howarth and colleagues analyzed data from published sources, industry reports, and Powerpoint presentations from the Environmental Protection Agency.
The researchers compared estimated emissions for shale gas, conventional gas, coal (surface-mined and deep-mined), and diesel oil, taking into account direct emissions of CO2 during combustion, indirect emissions of CO2 necessary to develop and use the energy source and methane emissions, which were converted to equivalent value of CO2 for global warming potential.
The study, published in the journal Climatic Change Letters, is the first peer-reviewed paper on methane emissions from shale gas, and one of the few exploring the greenhouse gas footprints of conventional gas drilling.
Most studies have used EPA emission estimates from 1996, which were updated in November 2010 when it was determined that greenhouse gas emissions of various fuels are higher than previously believed.
“We are highlighting unconventional gas because it is a contemporary problem for us in upstate New York, and because there is a big difference between developing gas from an unconventional well and a conventional well, for the mere reason that unconventional wells are bigger,” says Tony Ingraffea, professor of engineering.
The hydraulic fracturing process lends itself to more leakage because it takes more time to drill the well, requires more venting, and produces more flowback waste.
“A lot of the data we used are really low quality, but I’m confident they are the best available,” Howarth says. “We want to go out into the Marcellus shale and do micrometeorological fluxes of methane at the time of venting and get a real number on this, which has never been done. We’re optimistic we can get funding and do that over the next year.”
The researchers say they have attempted to be conservative in their analysis and have tried to not exaggerate the findings.
“We do not intend for you to accept what we’ve reported as the definitive scientific study in regards to this question,” says Ingraffea. “It’s clearly not. “What we’re hoping to do with this study is to stimulate the science that should have been done before. In my opinion, corporate business plans superseded national energy strategy.”
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