By SETH BORENSTEIN, AP Science Writer

WASHINGTON (AP) — Cheap and plentiful natural gas isn't quite a bridge to a brighter energy future as claimed and won't slow global warming, a new study projects.

Abundant natural gas in the United States has been displacing coal, which produces more of the chief global warming gas carbon dioxide.

But the new international study says an expansion of natural gas use by 2050 would also keep other energy-producing technologies like wind, solar and nuclear, from being used more. And those technologies are even better than natural gas for avoiding global warming.

Computer simulations show that emissions of heat-trapping gases to make electricity would not decline worldwide and could possibly go up, says the study, released Wednesday by the journal Nature.

Unconventional techniques such as high-volume hydraulic fracturing and ultra-deep water drilling have increased global supplies of natural gas so much that prices are now expected to remain relatively low for years to come. That makes generating electricity with natural gas cheaper than it otherwise would be, and makes it harder for wind and solar to compete

Five teams of experts from around the world, using five different sets of computer model simulations, looked at what would happen if natural gas — also known as methane — remains cheap and plentiful and nothing else changes, such as policy mandates. They all came to the same conclusion.

"It doesn't reduce climate change," said study lead author Haewon McJeon, an economist at the U.S. Department of Energy's Pacific Northwest National Laboratory.

Two computer models even found that when considering other factors like methane leaks, cheaper natural gas could lead to more trapping of heat by greenhouse gases, the mechanism that drives global warming. Methane traps even more heat than an equivalent amount of carbon dioxide.

But because the models differed so much on that projection, it is hard to conclude that more natural gas will worsen the problem, McJeon said.

"The scary thing about this paper is that it does make sense," said Gregg Marland, an expert in tracking fossil fuel emissions at Appalachian State University in Boone, North Carolina. Marland, who wasn't part of the study, said the combination of leaking methane and displacing cleaner fuels is a problem.

The results are similar to an earlier study by Duke University professor Richard Newell, who used to head the federal government's Energy Information Administration.

Granger Morgan, an engineering and public policy professor at Carnegie Mellon University who wasn't part of the study, said it undercuts the argument "that cheap abundant gas will serve as a bridge to a low-carbon future."

U.S. Energy Secretary Ernest Moniz last year in a town hall credited the natural gas boom with helping the United States decrease its carbon dioxide emissions over the last few years.

"The way to look at it is as kind of a bridge to a very low-carbon future," Moniz said. He said it allows the U.S. more time to develop cleaner technologies, such as wind, but "the key is, buying time is not very useful if you don't use the time."

But energy department officials said the new study ignores the effect of existing and future policy changes to encourage renewable energy. Since 2008, the amount of electricity generated by wind power has tripled and the amount from solar power has increased more than tenfold, according to U.S. the Energy Information Administration.

The Obama administration "is aggressively advancing energy technologies that will help reduce greenhouse gas emissions," energy department spokesman Bill Gibbons said in an email statement about the study.

The new results show it's important to have a climate policy to go with cheap natural gas, said experts who weren't part of the research.

Newell said that if a broad climate policy is enacted, "having abundant natural gas could be very helpful by making it cheaper for society to achieve climate goals."

Michael Oppenheimer, a Princeton University geoscience and international affairs, also emphasized the importance of policy changes.

"No one should accept natural gas as a windfall," he said.

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Online:

Nature: http://www.nature.com/nature

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Seth Borenstein can be followed at http://twitter.com/borenbears