Switching from coal to natural gas for power generation won't do much to reduce U.S. greenhouse gas emissions and might even raise them slightly, in part because it will discourage the use of carbon-free renewable energy, according to a study released Wednesday.

Increased use of natural gas has been widely credited with having reduced U.S. carbon dioxide emissions in recent years. But the new study, published in the journal Environmental Research Letters, finds that between 2013 and 2055 the use of natural gas could reduce cumulative emissions from the electricity sector by no more than 9 percent, a reduction the authors say will have an insignificant impact on climate. The power sector accounts for around a third of U.S. emissions.

The researchers—from the University of California, Irvine; Stanford University; and the nonprofit organization Near Zero—examined varying combinations of natural gas supply and climate policies. In some scenarios, they found that use of natural gas would actually boost emissions from the power sector by up to 5 percent.

The findings come on the heels of the United Nations climate summit in New York City, which was attended by President Barack Obama and other world leaders and was meant to set the stage for subsequent talks in Lima and Paris. U.S. leadership on reducing the greenhouse gases that contribute to climate change is considered by many to be critical in getting other nations to commit to action beyond 2020.

Natural gas has been promoted as a "bridge fuel" even by some environmentalists because it emits half as much CO2 as coal to produce a given amount of electricity. Coal currently accounts for 39 percent of the nation's electricity generation. (Vote and comment: "Can Natural Gas Be a Bridge to Clean Energy?")

"We were wondering, what about the effects outside of this direct coal and gas comparison," said Christine Shearer, a postdoctoral scholar at UC Irvine and a co-author of the new study. "What about the effects on electricity use and renewable electricity use?"

Delaying Solar and Wind

Many recent studies about the emissions impact of natural gas focus on methane leakage during production. Methane, the main component of natural gas, is itself a potent greenhouse gas.

A study published earlier this year found that methane emissions from the natural gas industry were likely 50 percent higher than previous government estimates, but that switching from coal to natural gas would still cut greenhouse gas emissions.

Rather than focusing just on methane leakage, the authors of the ERL paper surveyed 23 experts to get their predictions about future natural gas supply and then fed those assumptions into a model of the energy system. They found that even if little or no methane leakage occurs, natural gas doesn't do much to help reduce the greenhouse gases that contribute to climate change.

An abundant supply of natural gas "delays up to decades the time period over which renewable energies become economically competitive," the researchers write. And if natural gas makes energy cheaper, the study argues, people will use more energy rather than cut back to save money.

Those effects "essentially canceled out the climate benefits of substituting natural gas for coal, regardless of the leakage rate," according to the study. It also found that in the absence of a climate policy, natural gas does not have a "noticeable impact" on the use of nuclear energy or carbon capture and storage (CCS) at coal plants—because without specific encouragement from the government, new nuclear and CCS plants are unlikely to be built anyway.

In its proposed emissions rules, the Environmental Protection Agency set a national goal of reducing emissions from the power sector by 30 percent by 2030. Boosting natural gas generation is one option EPA has recommended as states seek ways to meet the carbon reduction targets imposed on them by the plan.

"We're very glad to see the EPA moving forward with the regulations, because it's been a long time coming," said Shearer. "But we do think that our study does have some caution for what they're doing."

Shearer said that gas might be viewed as a way to provide backup power for renewable energy such as wind and solar but that the study's results warn against "building a new generation of fossil fuel plants that will lock us into decades more fossil use that is hard to transition out of."

Another recent study warned that climate models had not taken into account billions of tons in "committed" emissions from existing plants over the next few decades. Building more natural gas plants, Shearer said, simply extends that commitment to fossil fuels.

Seeking Bigger Emissions Cuts

A 2012 study co-authored by Ken Caldeira, a researcher at Stanford University's Carnegie Institution for Science, concluded that natural gas could cut the warming effect of emissions compared with coal by 20 percent over 100 years. (See related story: "Natural Gas a Weak Weapon Against Climate Change, New Study Asserts.")

Caldeira said via email that although his research looked only at the physical aspects of the energy and climate system, Shearer and colleagues have "taken a further step back, and integrated economic feedbacks in their analysis."

The economic effects described by the study "make expansion of the natural gas industry look less helpful than ever," he said.

Steven Hamburg, chief scientist with the Environmental Defense Fund, a nonprofit organization that cautiously supports natural gas development, said that the new research is "asking the right questions," but questioned some of the paper's assumptions, including the idea that people would use so much more energy as a result of cheap natural gas that it would cancel out the benefits.

"Electricity demand has actually been dropping recently" because of increases in efficiency, Hamburg pointed out. "We have to be very careful in using a study like this in drawing those robust 'natural gas can't help' [conclusions]," he said.

Hamburg agrees with Shearer's overarching point, which is that the U.S. needs to transition away from fossil fuels. "If we want to be serious about reducing emissions and helping avert the worst effects of climate change," Shearer said, "we really need to look at what's effective."

What's effective, she went on, is a strong U.S. policy that limits carbon and supports the growth of renewable energy, "not just relying on natural gas and thinking that will solve the problem. It won't."