Shale gas, a promising clean energy solution, faces a major challenge from a new study that concludes it may have a heavier greenhouse gas footprint than coal.

A Washington consensus formed over the past couple years about what the immediate energy future for the country might look. Recent discoveries and technical advances in extracting gas from shale rock formations had analysts and politicians thinking that they could simply frack their way out of our nation's energy problems. After all, natural gas plants are fairly inexpensive to build, the resources were domestic, and burning gas has about half the carbon footprint of coal, so why not bet the near future of our nation's electric grid, gas proponents said.

But fracking, the nickname for hydraulic fracturing, the process by which inaccessible gas is made available, has always been a questionable environmental practice. Locals in areas where this particular type of resource extraction is occurring have sometimes called its "clean energy" status into question.

Now, The Hill reports that Bob Howarth, a Cornell ecologist and biogeochemist, will release a study declaring that the lifecycle emissions from shale gas development and combustion are worse than coal's. If verified by other scientific studies, the finding could force a major rethink of the use of shale gas as a tool in our kit to combat climate change.

As of yet, we're not sure exactly what the methodology of the study might be, but we do know that Howart claims that the methane emissions caused by shale gas development offset the gas' carbon advantage over coal. The slide above is drawn from a talk that his team delivered at Cornell on March 30 of this year. It shows that, according to their calculations, shale gas is substantially greenhouse gas-heavier than coal. This estimate takes a 20-year time horizon into account because methane is a more potent greenhouse gas on shorter time-scales, but even at the 100-year level, Howart's team found shale gas to be comparable to coal in total greenhouse gas impact.

UPDATE: While the Howart paper appears to be working its way through the peer review process, a preliminary set of conclusions has been available. It's also worth noting that these types of estimates are generally the subject of contentious debates between various interest groups.

So far, fossil fuel developers and environmentalists have found some common ground in natural gas. It's not emission free, but it's not coal either. And in the name of battling climate change, many greens have been able to justify support for shale gas under the "anything but coal" banner. Now, just the appearance of the the study may cause the unlikely bedfellows who've been supporting shale to wake up and realize with surprise that they've been consorting with the enemy.