At first glance, the recent shale-gas boom in the United States looks like excellent news for efforts to slow climate change. Natural gas is nudging aside dirtier coal in the electric-power sector, which is driving down U.S. carbon-dioxide emissions.
But the one huge caveat in this story has always been methane.
As all that natural gas gets drilled and extracted and processed and transported, some of it can leak out into the atmosphere as methane. And methane is a potent greenhouse-gas in its own right, trapping nearly 25 times as much heat as carbon-dioxide over a 100-year period.
That can shift the calculus. In theory, burning natural gas for electricity emits about half the carbon-dioxide that you get from burning coal. But if the methane "leakage rate" from all that natural-gas infrastructure starts creeping up past 3.2 percent, a recent PNAS study found, then suddenly natural gas starts to lose its climate advantage. And no one really knows what the leakage rate is.
That brings us to a big new study from the World Resources Institute, which tries to compile everything we know about methane leaks. The bad news: We have no idea how much methane is actually seeping out of our natural-gas wells and pipelines. The good news: The technologies to plug those leaks are readily available, but new regulations may be necessary to make sure they're widely adopted.
So how much methane is actually leaking? The authors take a look at all the existing studies on methane leakage. Estimates can vary widely, but "the weight of evidence suggests that significant leakage occurs during every life cycle state of U.S. natural gas systems." That includes leaks from drilling, production, processing, and distribution:
Notice that there's no definitive number for how much methane is actually leaking. "There's a lot of variability in these studies," explains James Bradbury, one of the co-authors of the WRI paper, in an interview. "It can vary from region to region, from basin to basin. It often depends on the operators involved."
And the current estimate by the Environmental Protection Agency that leakage is only around 2.4 percent is essentially an educated guess, based on a number of assumptions rather than direct measurements.
So, as a first step to getting a handle on this problem, the paper recommends that the EPA develop much more comprehensive measurements of actual leakage. That won't be easy — there are half a million natural-gas wells around the country, and hundreds of thousands of miles of pipeline — but it's a key first step.
Is it possible to plug those leaks? The next step, the WRI paper argues, is to try to reduce the leakage rate to around 1 percent — which would ensure that natural gas is cleaner than coal when used for electricity, and cleaner than diesel fuel when used for transportation.
Leak-plugging technologies do exist. For instance, plunger lift systems can allow drillers to remove excess liquid from their wells without letting a whole bunch of methane escape into the air. Similarly, more efficient "low-bleed" pneumatic devices can cut down on leaks throughout the system. As could better monitoring and repair systems.
In fact, simply adopting those three technologies mentioned above, the report estimates, could cut methane leaks by one-third and likely get the leakage much closer to 1 percent in the coming years. Here's a key chart:
What does this chart show? The red line is WRI's best current estimate of greenhouse-gas emissions (including methane) from all natural gas activities. The blue line shows WRI's estimate of future emissions after recently proposed air-pollution regulations at fracking wells take effect. (The steps that drillers will have to take to reduce volatile organic compounds from these wells will also curb methane leaks.)
The purple line, meanwhile, shows estimated future emissions if the EPA and state agencies required just three new technologies throughout the natural-gas infrastructure: plunger lift systems,leak detection and repair, and low-bleed pneumatic devices. And,with an additional five technologies,the country could get down below hoped-for 1 percent methane leakage rate. That¹s the green line.
"What we show is that minimizing leakage is definitely possible with cost-effective technologies," Bradbury says. "But this isn't likely to happen on its own. Better policies are going to be necessary."
That could mean state regulators, but it may mean the EPA. Currently, states can vary quite widely in how strictly they regulate methane emissions and other air pollutants from shale-gas fracking and natural-gas infrastructure. Some states, like Colorado and Wyoming, have been experimenting with fairly advanced regulations. But others, like Pennsylvania and Ohio, aren't quite there yet.
"A lot of states are still pretty lax on this issue," says Bradbury. "They're still catching up with this recent boom."