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The nation's natural gas boom has cut the amount of coal that's burned to generate electricity. That's a good thing for the climate because it means less carbon dioxide in the atmosphere. But some scientists have worried that leaks of natural gas could wipe out that advantage because gas itself is mostly methane, which is a potent greenhouse gas. A new study in this hotly contested issue finds that natural gas can still be cleaner than coal. NPR's Richard Harris reports.

RICHARD HARRIS, BYLINE: The natural gas boom in this country is fueled by a technology called fracking. Water, sand and chemicals are injected into wells to release far more gas than conventional drilling can. But David Allen at the University of Texas at Austin says this technology took off before anyone really understood how much natural gas leaks out in the process.

DAVID ALLEN: And we wanted to go out and collect some of the first data on some of the new types of operations that under way in natural gas production and what the methane emissions are.

HARRIS: He got funding from the Environmental Defense Fund, as well as support from nine major companies, which volunteered to participate in the study. And his conclusion is that currently the EPA greatly overestimates methane emissions from a new well that is being prepared to produce gas for the first time. The EPA also greatly underestimates emissions from wells that are already in production. But when you add the whole thing up...

ALLEN: Our total projected national emissions are very similar to the most recent national estimate for this part of the natural gas supply chain.

HARRIS: And that's potentially good news for advocates of natural gas because it supports the argument that, if done right, natural gas can be much better for the climate than coal. The study is published in the Proceedings of the National Academy of Sciences. It suggests ways to make natural gas production cleaner than it is today. For example, it turns out that there's a lot of methane leakage from operations that separate natural gas from oil and water that come up the well at the same time.

ED HANCE: That was the biggest surprise for me as an operator.

HARRIS: Ed Hance is from Pioneer Natural Resources, a natural gas company that works mostly in Texas and participated in the study.

HANCE: I would say that's the primary area we need to focus going forward, as far as practices where we can have the opportunity to reduce emissions further.

HARRIS: Now it's important to note that the study relied on nine companies, like Pioneer, who volunteered to be studied. So Bob Howarth at Cornell University says the results from the 190 study sites are not necessarily representative of the industry as a whole.

BOB HOWARTH: I would view this as a best-case scenario for what industry can do to reduce methane emissions when they want to.

HARRIS: Something more resembling a worst-case scenario is a study out in Utah, which sampled the air in an entire area rather than tracking emissions down to specific pieces of equipment and practices.

HOWARTH: And they're finding methane emissions that are 10 to 20 times higher than this new study and I think are probably more representative of at least those western gas fields when industry does not realize they're being watched.

HARRIS: Figuring out what practices are responsible for large methane emissions like those in Utah will take more work. Steve Hamburg, chief scientist at the Environmental Defense Fund, says his organization is funding 16 studies to look at the entire natural gas system in this country. This new study, focusing only on production, is just one part of that.

STEVE HAMBURG: Regrettably, we need another year, and then we'll have all of these pieces together and then we really can get a clear - much clearer picture of what's going on.

HARRIS: And at stake isn't simply gas production in the United States. Natural gas is taking off globally. So Hamburg says this is an opportunity to fix what's wrong here and to spread those best practices around the world. Richard Harris, NPR News.

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