FORTUNE — What can the executive director of the Sierra Club and a Shell executive agree on? That natural gas can serve as a bridge fuel in the United States, carrying the country from its dependence on oil to a widespread use of renewables.

The main point of contention is the length of that bridge.

Panelists on both sides of the fracking divide gathered Tuesday at Fortune’s Brainstorm Green conference in California to discuss the future of natural gas in the U.S.

Ultimately, the country will ideally transition to clean fuels including nuclear energy, solar and wind power, says Pat Wood, former chairman of the Federal Energy Regulatory Commission and currently a principal at Wood3 Resources. “Between now and then, God gave us a great big gift here with fracking.”

Fracking is a well-stimulation method used when drilling for natural gas. Oil and gas companies have used the method on vertical wells since the 1950s. But in 2003, Halliburton (HAL) started fracking along horizontal wells, allowing companies to extract much more natural gas than previously conceived.

In simple terms, fracking creates fissures in the shale rock alongside a well, then floods those fissures with a mixture of sand and water to push gas out of the cracks and up the well.

Fracking and gas drilling have caused controversy across the country. Some Americans, especially those living near the Marcellus Shale in the northeast, have claimed that fracking has poisoned their water, or, at the very least, their quality of life. Two states that touch the Marcellus – New York and New Jersey – have temporarily banned fracking.

“The real issue is how you properly construct a well,” says Russ Ford, the vice president of onshore gas, upstream Americas for Shell’s exploration and production arm. Most of the pollution problems attributed to fracking happen when companies don’t line their wells properly, he says. Ford claims that when wells are properly built, as they usually are, fracking is safe.

Safe enough, in fact, to become an even greater portion of the U.S. energy portfolio going forward. Ford would be happy, he says, to displace dirty coal with natural gas.

That may not solve America’s unhygienic fuel problem, says Mike Brune, the executive director of the Sierra Club. The Sierra Club’s long-term goal is to retire one-third of U.S. coal plants used for power generation by 2030. Over that period of time, Brune says, natural gas production will ideally remain stable if not decline slightly until more information is available on the safety of natural gas drilling, and whether natural gas is truly a green fuel.

But if you ask the industry, the wheels making natural gas a major global fuel source are already in motion. And fracking, according to Wood and others, is the blessing keeping those wheels good and greased.

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