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."

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."

In their push for more natural gas, drilling operators are increasingly using a process called hydraulic fracturing ("fracking"), which shoots vast amounts of water, sand and chemicals deep underground to break apart rock and release the gas. More frequently, this process also involves drilling down and then turning horizontally.

West Virginia leaders are hoping this practice expands as gas companies seek to tap into vast reserves contained in the Marcellus Shale, a formation that stretches across 95,000 square miles from southern New York and into eastern Ohio.

Last month, lawmakers approved new tax credits to try to encourage oil and gas industry growth, but declined an outcry from citizens -- and the recommendations from the state Department of Environmental Protection -- for new regulations on drilling. As advocates of those regulations have pushed for a special session on the issue, industry groups have launched a new public relations campaign promoting their economic contributions to the state.

On Monday, the gas industry-sponsored blog "Energy In Depth" attacked the new paper and questioned some of the methods used by the researchers. The group also criticized Howarth because he has talked about his scientific research at public meetings and government comment periods in New York, where Marcellus Shale drilling is a heated issue.

Separately, Christopher Van Atten, an industry consultant with the firm M.J. Bradley & Associates, questioned some of the assumptions used in Howarth's study and said that even the authors noted there was great uncertainty about some of the data used.

In a news release, Howarth said the new study is not intended as "the definitive scientific study in regards to this question."

"It's clearly not," Howarth said. "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."

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.