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Not surprisingly, their conclusion has drawn fire from the oil and gas industry. Less predictably, another set of researchers from the same university also questions the finding.
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The first group of researchers said their work found that greenhouse gases produced by the U.S. natural-gas industry will grow from 17 to 23 percent during the next 20 years as shale gas continues to replace conventional natural gas.
Responding to their critics, they recently defended and reiterated their findings using fresh data from the federal Environmental Protection Agency.
Based on its large contribution of methane, shale gas development results in greater greenhouse gas emissions than either oil or coal, according to the researchers. They believe that shale gas is not suitable as a “bridge fuel” from fossil fuels to renewable energy, an assertion held by advocates of shale gas exploration.
Most dramatically, their study posits that the Earth’s temperature will increase by 1.5 degrees Celsius over the next 18 years or less if methane emissions are not better controlled.
“Society needs to urgently address global warming,” Robert Howarth, a professor in Cornell’s Department of Ecology and Evolutionary Biology, said this year. “To do so will require other technologies, truly green energy technologies, and not relying on shale gas.”
The study comes amid recent air quality studies conducted in Colorado that have shown the presence of pollutants associated with oil and gas development. One study showed that Erie contained higher levels of pollution, including methane, propane and butane, than two much larger metropolitan areas – Houston and Pasadena, Calif.
Hydraulic fracturing, also known as fracking, involves pumping a mixture of water, chemicals and sand deep below ground to release gas in shale. Following hydraulic fracturing, some methane flows to the surface and escapes into the atmosphere, the study says.
“Natural gas, including shale gas, is mostly methane, so even small levels of gas venting and leakage contribute very heavily to the greenhouse gas footprint,” Howarth said.
He estimated that 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.
Hydraulic fracturing is more prone to leakage, Howarth said, because it takes more time to drill the well, requires more venting and produces more flowback waste.
The natural-gas industry already leads in methane pollution by contributing 39 percent of the total amount of emissions, according to the study. A key greenhouse gas that contributes to climate change, methane traps heat more efficiently than carbon dioxide, according to the EPA.
Researchers found that methane from all sources will make up 44 percent of all so-called greenhouse gas emissions in the next two decades.
Doug Flanders, director of policy and external affairs for the Colorado Oil and Gas Association, said a number of studies have refuted the researchers’ conclusions.
“All showed many of the problems with this study,” Flanders said.
Researchers at Energy In Depth, an educational outreach campaign by the Independent Petroleum Association of America, have written multiple blog posts castigating the study. Their website notes that another study from Cornell University in Climatic Change also has challenged the original study.
“The real question is, with all of the evidence clearly contradicting Howarth’s thesis, how does anyone still consider it credible?” Simon Lomax, research director for Energy In Depth, wrote in an email.
The opposing report, conducted by three other Cornell University researchers, calls the original study “seriously flawed.”
“The assumptions used by Howarth et al. are inappropriate and … their data, which the authors themselves characterize as ‘limited,’ do not support their conclusions,” the study states.
Responding to their Cornell colleagues, the researchers led by Howarth said in their most recent study that the criticisms had “little merit” and that “we stand by the analysis and conclusions we published.”
Tony Ingraffea, another of the researchers on Howarth’s team, said the researchers were especially careful in drawing their conclusions.
“We’ve tried to be conservative all along; we’re not trying to be hyperbolic in our statements,” he said in an article published by Cornell.