Drilling and fracking can release methane, a potent greenhouse gas, but how much is unclear

Natural gas is billed as a cleaner energy source because it emits about half the carbon dioxide as coal does when burned. However, sloppy drilling can release methane, the primary component of gas, into the atmosphere. It's 25 times more potent as a greenhouse gas than carbon dioxide, and mostly escapes during flowback, "when fracking fluids, water and gas flow out of a well after drilling but before the gas is put into pipelines," reports Renee Schoof of McClatchy Newspapers. (McClatchy photo: Gas drilling rig)

The Environmental Protection Agency found that the oil and gas industries emit 40 percent of all methane coming from the U.S. The industries say that number is overblown because they burn or capture escaped methane before it enters the air, but a Cornell University study released last April concluded that the EPA estimate was too low.

Schoof reports there's not enough data about exactly how much methane is released. "Even small leaks can wind up undoing most of the global warming benefit we think we're getting when we substitute natural gas for coal," said Mark Brownstein, Environmental Defense Fund natural gas and oil team director. EDF isn't opposed to fracking, but it does want to work with energy companies to reduce methane emissions. (Read more)