WASHINGTON—Extracting natural gas from shale formations using hydraulic fracturing generates more greenhouse-gas emissions than burning coal, according to a new study that drew immediate attacks from oil and gas interests already facing pressure from lawmakers and regulators worried about the environmental effects of shale-gas development.
The study, conducted by professors at Cornell University, found that natural gas obtained from shale formations using a process known as "hydraulic fracturing" releases large amounts of methane. When methane emissions are taken into account, natural gas from these shale formations produces more greenhouse gases than coal and coal-fired electricity generation over a 20-year time horizon, the study said.
Until now, Democrats on Capitol Hill and some environmental groups have looked to natural gas as a "bridge fuel" that could help the country make the transition from carbon-heavy fossil fuels such as coal to cleaner sources of energy.
"That is what people have tended to focus on in the past," said Robert Howarth, one of the authors of the report and a professor of ecology and environmental biology at Cornell. "I did not expect the methane number to be as big as it is."
The American Petroleum Institute, a trade group representing the oil and gas industry, said the study relied on "weak" data regarding methane leaks and didn't take into account the efficiency of natural gas when used for power generation.
"The data is pretty weak for the shale gas emissions," said Russell Jones, senior economic adviser at the American Petroleum Institute. "The basis for those precise numbers is not very precise."
The study complicates the politics of natural gas at a time when the Obama administration and members of Congress say they want to encourage natural gas production as a way to replace coal and oil in electricity generation and transportation.
Last month, President Barack Obama directed Energy Secretary Steven Chu to find ways to improve the safety of natural-gas production, and praised natural gas as a domestically produced fuel source that could reduce the country's dependence on foreign oil and reduce carbon pollution.
U.S. Senate lawmakers, meanwhile, are in the process of developing a nationwide clean-energy standard after Mr. Obama said he wanted the country to generate 80% of electricity from clean-energy sources by 2035.
The Cornell study "certainly suggests that, if you're going to include natural gas in such a system, you have to get better data and account for these emissions," said Dan Lashof, director of the Natural Resources Defense Council's climate center.
The new study attempts to measure the amount of greenhouse-gas emissions released during the production and use of the fuels. It found that, when natural gas is being produced, up to 8% of the methane in it escapes into the atmosphere over the lifetime of a well. Much of the methane leaks during the fracturing process, when companies fracture open the rock formations to increase the flow of natural gas.
The study also raised additional questions about the process of hydraulic fracturing, which has been criticized for its potential effects on drinking water. The Environmental Protection Agency is currently conducting a study to determine whether the process contaminates water supplies.
The Cornell study is expected to be published this week. Dow Jones Newswires obtained an advanced copy. The report's contents were first reported by The Hill.