CHARLESTON, W.Va. -- When companies use hydraulic fracturing to drill for natural gas, the resulting energy production contributes as much -- and maybe more -- to global warming as coal-fired electricity, according to a scientific paper due out this week.
Researchers at Cornell University warn that their findings contradict the conventional wisdom that natural gas could become a "bridge fuel" to help the nation transition from coal to wider use of alternative and renewable sources.
"We need to look at the true environmental consequences of shale gas," said Robert Howarth, a Cornell ecology professor and lead author of the study.
Howarth and two colleagues calculated estimates of the greenhouse-gas footprint of natural gas produced using advanced techniques to release gas reserves from shale formations deep underground. Then they compared those estimates to greenhouse impacts from coal and oil, based on energy content of the fuels.
"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," the study said. "Compared to coal, the footprint of shale gas is at least 20 percent greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years."
The study is due to be published later this week in the peer-reviewed journal Climate Change Letters. But copies were provided to the media without any embargo after The Hill's website published a report on the study Sunday. ProPublica, a nonprofit journalism group, had previously detailed some findings of the research.
Howarth and his colleagues focused on drilling's emissions of methane, which is a more potent but less long-standing greenhouse gas than carbon dioxide. Natural gas is composed largely of methane, but the gas is also released during the drilling of wells, by routine venting and equipment leaks, and during gas processing and transportation, the study explains.
"The large [greenhouse gas] footprint of shale gas undercuts the logic of its use as a bridging fuel over coming decades, if the goal is to reduce global warming," the study said. "We do not intend that our study be used to justify the continued use of either oil or coal, but rather to demonstrate that substituting shale gas for these other fossil fuels may not have the desired effect of mitigating climate warming."