Fracking's Methane Trail: A Detective Story

There are a lot of cheerleaders for the nation's natural gas boom — in part because they believe it's a lot cleaner than dirty coal. It's pretty well-known that power plants that burn coal pump out far more greenhouse gases than power plants that run on natural gas.

But there's a hitch: We don't really know how much air pollution is created when companies drill for natural gas.

'Not So Many Measurements'

Well heads, storage tanks and pipelines all leak methane in sprawling gas fields.

"We need to know a lot about methane itself, which is natural gas, if we're worried about climate change," says energy consultant Sue Tierney, "so that we don't automatically think that gas is so much cleaner than coal."

Methane is a very potent greenhouse gas. It's very effective at trapping heat in the atmosphere.

"Fifty years from now, are we really going to be wondering if we really screwed up because we went on this big gas boom? You really wouldn't want to be messing that up," Tierney says.

She says that's why it's so important to study air pollution from natural gas production now.

Tierney was on an Energy Department advisory panel that recommended that gas companies start measuring and reporting their air emissions.

The way it is now, the government doesn't really know how much methane comes from gas production.

"What the official estimates are based on generally are not so many measurements, but rather estimates," says Greg Frost, an air pollution expert for the National Oceanic and Atmospheric Administration. "They really are based on maybe a measurement here or there, but then they're largely based on extrapolation."

To really find out how much methane is being leaked, many scientists say you need to take lots of direct measurements: How much methane is coming off a well, or a pipeline, or a whole gas field?

Finding The Methane Source

At the foot of the Rocky Mountains, there's a tall tower that tipped off scientists that estimates are poor substitutes for measuring. Imagine an open metal structure as tall as the Eiffel Tower and in the shape of a Toblerone chocolate box. A tiny elevator runs up the middle.

For the past few years, this tower has been Gaby Petron's muse, spewing out numbers about air pollution. Petron works for the NOAA's lab in Boulder, Colo.

"I look for a story in the data. ... You give me a data set, I will study it back and forth and left and right for weeks," she says.

Four years ago, tubes at the top of the tower started sucking in samples of air every day. Petron noticed that data from the tower showed surprising levels of methane.

"Whatever was in the air here was really different than anywhere else," she says.

Petron's next step was to try to find out what was creating that methane. She talked a colleague into turning his Prius into a mobile lab for taking air samples.

"You want to see the invisible. You want to see what's in the air, and you want to know exactly where the air is coming from," Petron says.

She got into the Prius and headed east, in the direction of the tower. She took a good look around for potential sources of all that methane.

"Every time we drive east, the methane would go up. And I'm like, why is that? And then you come here and you see cows," she says, "and you're like, OK, maybe it's the cows."

Cows burp methane — but they weren't a match. They didn't have the right chemical fingerprint. Rotting garbage produces methane, too, but a nearby landfill wasn't a match, either.

Next on her list: the gas and oil fields northeast of the tower. As she drove near, methane levels on her computer screen in the Prius spiked.

She had her match.

"So that's when you have your moment. You're like, all right, the story is right there. It's really not the landfill, it's really not the cows," she says. "It's really all the oil and gas equipment and activities that are going on in the region. And it's not new. It's always been there. We were just not measuring it."

Petron's measurements show the gas and oil fields in Northern Colorado are probably leaking twice as much methane into the air as the industry says they are.

"I think the atmosphere is a good way to look at things in terms of emissions because it's not lying," she says.

She published her work in the Journal of Geophysical Research a couple of months ago.

Making The Most Of Estimates

So why don't gas companies measure their methane emissions? Cindy Allen, who heads the environment team for a drilling company called EnCana, says it's not doable. There are a lot of gas fields, and some of them sprawl over hundreds of square miles.

Allen says it would take too much work for companies to maintain air pollution monitors near each well site.

"And they're very expensive. It's not realistic to install such devices on every single emissions source that there is," she says.

Howard Feldman of the American Petroleum Institute says companies are trying to improve their estimates. His trade group is working on a new survey of methane emissions from tens of thousands of wells.

But Feldman says more measurements like the ones that came from that NOAA tower are needed, too.

"One in and of itself isn't sufficient. Both are valid, and both add to the information that we have," he says.

Feldman says it's in the industry's interest to find leaks and capture methane. That way, they can sell it instead of losing it to the atmosphere.

By Elizabeth Shogren Listen to the story @NPR.org