Is shale gas good for us or not? Most of that argument has been over the potential risks that hydrofracking for shale gas might pose to water supplies—risks that were highlighted again this week when the Environmental Protection Agency (EPA) came to Dimock, PA, to test groundwater in the area. You might know Dimock from the anti-fracking film Gasland—a group of residents have claimed for years that fracking poisoned their water supply, and federal involvement indicates there may be more at stake.
But while water has been the focus of the fracking wars, there’s another debate going on over a hidden aspect of shale gas: its contribution to global warming. Conventional natural gas is by far the cleanest of the fossil fuels—not just in terms of toxic pollutants like ash or sulfur dioxide, but in terms of carbon as well, with a greenhouse gas footprint perhaps half that of coal. But a group of scientists at Cornell University, led by the ecologist Robert Howarth, challenged that consensus in a paper published last year claiming that shale gas might actually be worse for the climate than coal. Their conclusions were heavily criticized by the gas industry as well as some independent experts, and earlier this month another set of Cornell scientists—led by the geologist Lawrence Cathles—published a paper arguing that Howarth’s numbers were wrong, and that shale gas was indeed much less carbon-intensive than coal. And that paper in turn prompted another article by Howarth and his colleagues yesterday make the case that, no, they were right all along.
So what does this all mean—other than the fact that the Cornell faculty club may be getting a little testy these days? Is shale gas good for the climate or bad?
The truth is we can’t be entirely sure. That’s because the one fact that’s most important to nailing down the full greenhouse gas footprint of shale gas—the amount of methane that is spilled into the air accidentally during the production and transportation of gas—isn’t well known. And it isn’t well known in part because the oil and gas industry is famously tight with its data—there have been similar problems trying to find out the ingredients in fracking fluid—which leaves researchers to create models out of bad data. And that leaves a lot of room for interpretation.
In Howarth’s study—and in the follow-up released yesterday—he estimated that as much as 8% of methane from shale-gas production escapes into the atmosphere, where it’s a far more powerful greenhouse gas than carbon. Technically, methane—which is really just another word for natural gas—has about 23 times the global warming potential of carbon dioxide, though it doesn’t stay in the atmosphere as long. As a result, he concluded that gas from fracking could have a greenhouse gas footprint twice as great as coal over a 20-year time frame, and perhaps equal to coal over a century-long frame.
Cathles’s paper earlier this month, though, made the case that Howarth had overestimated the methane leaks from shale gas wells by as much as tenfold, and concluded that natural gas—from fracking or not—remained a bridge to a cleaner future:
In the short term, our energy needs should be satisfied mainly by those fuels having the fewest inherent environmental disadvantages,” Cathles and his co-authors concluded. “Those preferred fuels include natural gas.
Howarth, for his part, obviously disagrees:
We believe the preponderance of evidence indicates shale gas has a larger greenhouse gas footprint than conventional gas, considered over any time scale. The greenhouse gas footprint of shale gas also exceeds that of oil or coal when considered at decadal time scales, no matter how the gas is used. We stand by the conclusion of our 2011 research: ‘The large [greenhouse gas] footprint of shale gas undercuts the logic of its use as a bridging fuel over coming decades, if the goal is to reduce global warming.
Who’s right? Critics I respect, like Michael Levi of the Council on Foreign Relations, have cast a lot of doubt on Howarth’s original conclusions. And even if the climate benefits of shale gas are much less than advertised, it produces far less traditional pollution than coal—which makes a difference on public health. But the reality is that we need more information about potential methane leakages in gas production and transport—and we need stronger regulations to ensure that fugitive gas doesn’t make it into the atmosphere. Still, don’t expect the war of words—and scientific papers—over shale gas to end any time soon.