Ars does a nice job diving into the question of Methane burned vs. methane leaked: Fracking’s impact on climate change. "So what’s the bottom line? Is America’s shale gas revolution helping or harming efforts to reduce climate-changing greenhouse gas emissions? Most estimates put the amount of methane currently leaking into the atmosphere from shale gas in the neighborhood of two percent. Insofar as natural gas is displacing coal-burning power plants, it takes at least four percent leakage—up to nearly eight percent if the oldest, least-efficient coal plants are the ones displaced—for natural gas to fail to yield greenhouse savings over the short-term, 20-year timeframe."