The Cornell researchers acknowledge that the available data is incomplete, and industry groups were quick to counter their conclusions. Energy in Depth, a group representing independent U.S. petroleum producers, accused Howarth of using low-quality data to "jack up" the global-warming potential of methane. It also took issue with his decision to focus on the impacts over 20 years. Howarth, however, says that critical events in climate change are likely to happen in the next two decades, meaning that the short-term impact of methane is an important factor in measuring long-term climate consequences.

On the issue of data quality, Howarth concedes that he didn't have the best information to work with. "The reason is that all of the data come from industry sources ... and industry has not been very forthcoming," he says, adding that the EPA has proposed regulations that require better reporting on methane leakage. "Were the industry to comply, then more and better documented data could become available, and one could improve on our study."

Mark Jaccard, a professor of energy and materials research at Simon Fraser University, says he's not surprised by the findings of the Cornell study. But he suggests that the results are not an argument against shale gas. Instead, the study should be a timely call for stricter regulations. "Shale gas could be produced in a way that had very little emissions," he says.

Indeed, the Cornell study points to various ways that drillers and pipeline operations could reduce methane emissions by up to 90 percent. But, the study adds, "these technologies are currently not in wide use."