Weeks after Barack Obama promoted natural gas as a key part of U.S. energy policy in his State of the Union address, new research says gas drilling may be emitting far more methane and other pollutants into the atmosphere than current estimates suggest.

The work, performed by scientists with the National Oceanic and Atmospheric Administration, focused on Weld County, Colo., home to more than 20,000 gas wells. After years of monitoring and study, the researchers estimated that about 4 percent of the methane produced by these wells is lost to the atmosphere.

That's about twice as much as current estimates would suggest, and twice what the EPA assumes is lost nationally during gas drilling and production, said Gabrielle Petron, a lead author of the study.

"What I've learned in the past three or four years is that there's a lot we don't know, and the industry may not be aware of these leaks and how important they are," Petron, a researcher with NOAA and the University of Colorado, told InsideClimate News. "Until you go out there in the field and take measurements you may not have a sense of what is leaking and how much it's leaking."

Methane accounts for about 10 percent of greenhouse gas emissions nationwide. Leaks during the drilling, production and transmission of natural gas are the largest source, accounting for about a third of all man-made methane emissions.

In addition to methane, the researchers also found surprisingly high emissions of benzene, a carcinogen, and other pollutants.

Petron said the study, which is being published by the Journal of Geophysical Research, is the first to take atmospheric measurements of emissions from gas drilling. Current estimates are based primarily on isolated sampling and data provided by drilling companies, she said. States and the EPA use that data to build models for extrapolating emissions.

Advocates have been pushing the industry for years to capture more of the gases that leak during drilling and production. Jeremy Nichols, director of the climate and energy program at WildEarth Guardians, a New Mexico-based environmental group, said gas companies shouldn't wait for more studies to begin reducing emissions.

"At some point we should just realize there are really good policy solutions here," he said. "Fixing a leak in a pipe? That just seems like common sense. We shouldn't have to quantify how much is leaking before we do it."

Some drilling companies have begun to use "green completion," a technology that captures much of the emissions when wells are hydraulically fractured. And the EPA has created a voluntary program, Natural Gas STAR, that encourages drilling companies to capture and sell stray methane.

But Nichols said the new research shows that drillers could do better. He analyzed NOAA's new data and found that the emissions produced by Weld County's gas wells are equal to the carbon emissions of 1-3 million cars.

"No matter which way you slice it, that's a lot of greenhouse gas emissions, and that's just one county," he said.

In July, the EPA began creating the first federal regulations to reduce emissions during drilling and fracking.

In response to a lawsuit filed by WildEarth Guardians, the agency proposed new rules that would reduce smog-forming emissions by almost 95 percent, the EPA said. While the rules don't require drillers to target methane, the agency said limits on other pollutants would have the benefit of cutting methane emissions by a quarter. The EPA said it will release the final rules in early April.

The drilling industry has criticized the data that the EPA used for the rules, saying it over-estimates emissions. In comments to the agency, the American Petroleum Institute said the proposed rules are too burdensome. The group did not respond to requests for comment for this article.

Petron's work suggests that even with the EPA's proposed reductions, gas drilling could remain a significant source of greenhouse gases. Such emissions have caused some to question whether natural gas is much of an improvement over coal.

The gas industry and some environmentalists have said that gas emits about half as much climate-altering pollution as coal when burned to generate electricity. They've used that number for years to support using gas as part of a "bridge fuel" to a more climate-friendly energy future.

But when the methane emitted during drilling and production is included, the benefits shrink.

In late 2010, the EPA revised its estimates of how much methane leaks from wells and tanks during well development, saying it was twice as much as previously thought. Then in May 2011, researchers at Cornell published a study arguing that because of these emissions, and because methane traps far more heat than carbon dioxide over a 20-year time frame, natural gas may actually be worse for the climate than coal.

Many criticized the Cornell work, and subsequent research has found that gas is indeed cleaner than coal, even taking methane leaks into account. But the new research produced estimates similar to the ones the Cornell researchers used to build their models, suggesting that EPA's newer estimates may still be low.

The NOAA researchers' work began in 2007, when they started using a nearly 1,000-foot tower to measure air quality in the Denver area. The region was exceeding federal air quality standards for ozone, and the researchers wanted to find out why.

"When we started doing the measurements we were like, whoa, there's a problem here," Petron said.

Because Colorado had recently implemented strict emissions rules for gas drilling, the researchers had expected that Denver, the area's largest city, would be the primary source of pollutants. But the compounds they detected suggested another source, so they went into the field with mobile sampling stations and began testing. By comparing methane levels to corresponding spikes of other pollutants, like benzene, the group determined that gas activity, and not feedlots or cars, was the main source.

The new research can't be extrapolated nationwide, Petron said, due to differences in practices and climate between drilling areas. But she hopes policy makers and the drilling industry will see her study as a call to action and will replicate the work around the country.

"Until you go out there in the field and take measurements you may not have a sense of what is leaking and how much is leaking," she said. "I think we could have substantial reduction if we knew a little more what to target."

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