Natural gas may help the U.S. cut down on carbon dioxide emissions, but experts say relying on this "bridge fuel" will only delay the switch to renewable forms of energy.

Researchers at the University of California, Irvine, modeled energy use scenarios that could play out over the next forty years. They plugged in a range of predictions for the supply of natural gas, accounted for policies the U.S. government might adopt to address global warming and anticipated technological advances.

Abundant natural gas, supplied in part by the fracking and the shale gas boom, will likely further decrease coal use. However, it will also "delay the use and price-competititveness of lower-carbon renewable energy sources," writes lead author Christine Shearer and her colleagues in the report, published in Environmental Research Letters.

Using natural gas could reduce total greenhouse emissions but only by about 2 percent. Government action, such as levying a carbon tax or implementing cap-and-trade policies, would have more of an effect, reports Max Ehrenfreund for the Washington Post:

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.

The general message that natural gas isn’t a good bridge holds true even if leaks during production and delivery are eliminated, the researchers find.