A protester carries an anti-fracking sign on Sunday in New York. (Timothy Fadek/Bloomberg)

In his January State of the Union address, President Obama said that natural gas could be a low-emission "bridge fuel" that could allow the U.S. to help slow global warming. Demonstrators at Sunday's climate protest in New York apparently didn't get the talking points memo from the White House -- many carried signs calling for an end to fracking.

The reality is that shale gas probably won't have much effect on climate change either way, according to a new study published Wednesday. "If you increase the use of gas, that will actually delay the deployment of renewable energy," said Christine Shearer of the University of California, Irvine, one of the authors of the study.

Shearer and her colleagues modeled how the consequences for the climate in the next forty years would differ depending on how big the gas boom gets, how quickly solar technology develops, and what policies the federal government adopts to slow global warming. Their forecasts showed that the more natural gas is available, the less the energy sector will rely on renewable resources, and that the supply of natural gas will not have much effect on greenhouse gas emissions.

Abundant gas reserves will lower electricity bills and encourage people and businesses to burn more electricity, the authors find. Also, cheap energy from gas will make building new solar panels and wind turbines less attractive to investors. The paper predicts that a larger supply of gas might reduce or add to emissions slightly, depending on how well companies can keep gas from leaking.

These results largely confirm work published earlier this year by a pair of researchers at Duke University and a report published last year collating predictions from academics, government officials and the industry.

The authors did not consider how U.S. gas production would affect emissions in other countries, which is also a matter of debate.

Alan Krupnick of Resources for the Future, a research organization, agreed that natural gas was "a pretty rickety bridge," but he noted that the fuel may have other benefits unrelated to climate change. Besides carbon dioxide, other pollutants that are also less abundant in natural gas than in coal are more immediately harmful to human health, Krupnick said.

One argument that the industry often makes is that natural gas can make up for the weaknesses of renewable energy in a way that coal cannot. Production at solar panels and wind farms varies from hour to hour depending on the weather and the time of day, making it difficult for grid operators to plan where electricity will be routed and to ensure that there is enough to go around. Natural gas turbines, unlike coal-fired turbines, can be switched on and off quickly and efficiently in case the wind dies down or the sky clouds over.

Shearer said that her group's computer model did not account for variations in the supply of clean energy over the course of a day, but she doubted that doing so would change their results much.

Given a choice, Shearer said, utilities will choose natural gas if it is cheap and widely available. The forecast is different if the federal government mandates that utilities derive some percentage of their energy from clean sources, as many states have done already. This kind of mandate would do more to slow global warming if there is plenty of gas available, since the gas will replace coal, not renewable energy. Utilities will have to use solar and wind power even if gas is cheaper.

That said, if the federal government aims at reducing emissions, the largest reductions come from putting a price or a cap on carbon, according to the paper.