ALBANY -- As New York officials consider opening the state to the natural-gas drilling technique known as hydrofracking, a study from Cornell University warns that it drives global warming as much as emissions from coal -- or even more.

The peer-reviewed study, published this month in the journal Climatic Change, found that hydrofracking, which relies on a high-pressure mix of chemicals, water and sand to free gas trapped in deep rock formations, also releases into the atmosphere large quantities of methane, a potent greenhouse gas.

The study comes as national energy policy looks to natural gas as a greener alternative until renewable energy can be expanded. When burned, natural gas produces less carbon dioxide -- a greenhouse gas that an international scientific consensus identifies as the main cause of man-made climate change -- than other fuel sources.

The State Department of Environmental Conservation is expected to offer proposed rules for hydrofracking sometime this summer.

"The take-home message of our study is that for 20 years following development, shale gas is worse than conventional gas and is, in fact, worse than coal and worse than oil," said study author Robert Howarth, a biogeochemist at Cornell. "We need to look at the true environmental consequences of shale gas."

The gas industry, which already uses hydrofracking in Pennsylvania, Texas and West Virginia, immediately attacked the report. "This study lacks credibility and is full of contradictions," said Russell Jones, senior economic adviser at the American Petroleum Institute.

"The main author is an evolutionary biologist and an anti-natural gas activist who is not credentialed to do this kind of chemical analysis. The authors admit that the data used was of very low quality," said Jones.

Howarth said some data came from the American Petroleum Institute. "To set the record straight, I am not an evolutionary biologist. I am disappointed that the API has decided to attack me personally, but they are having difficulty in attacking the science, and so fall back on this instead," he said.

Problems with incomplete data stem from the industry's unwillingness to report methane emissions, said Howarth. After the U.S. Environmental Protection Agency proposed better reporting of methane leakage from gas wells, the industry sued to block the regulations, he added.

The study estimated as much as 8 percent of the methane in shale gas leaks during the life of a hydraulic shale gas well -- up to twice what escapes from conventional gas production.

Howarth, along with co-authors Anthony Ingraffea, a professor of civil and environmental engineering, and Renee Santoro, a research technician in ecology, analyzed data from industry reports, other published sources and the EPA.

"We do not intend for you to accept what we've reported on today as the definitive scientific study in regards to this question. It's clearly not," said Ingraffea. "What we're hoping to do is to stimulate the science that should have been done before."

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