The recent boom in U.S. natural gas production has been hailed as the cure to all America’s ills. Gas, its boosters say, can reduce household heating expenses, enhance energy security, create jobs, and lower greenhouse gas emissions.

That last part is crucial to winning over environmentalists. “Over its full cycle of production, distribution, and use, natural gas emits just over half as many greenhouse gas emissions as coal for equivalent energy output,” the green group Worldwatch Institute reported last August. But all of that may amount to a lot of hot air if researchers from Cornell University and the Environmental Defense Fund are right. Thanks to the little-known problem of methane leakage, in the short term at least, natural gas may be worse for the climate than other fossil fuels.

Natural gas is mostly methane, which is itself a heat-trapping greenhouse gas. And it leaks into the air at every point of the process of getting and using the fuel. The technology exists to capture the leaking gas at hydraulic fracturing – aka fracking – sites, but industry officials say it’s not worth the cost. With the price of natural gas having dropped 90 percent since 2005, that attitude is not likely to change soon.

Ramon Alvarez, a physical chemist who works at the Environmental Defense Fund, co-authored a study, published in April in the Proceedings of the National Academy of Sciences, that compares the impacts of natural gas with gasoline, diesel, and coal on the climate. His conclusion: “The amount of methane released can affect whether or not natural gas is a better fuel for the climate than other fuels.”

In February, researchers from the National Oceanic and Atmospheric Administration analyzed air samples from a region of Colorado where a lot of gas is being extracted through fracking. They found the air contained twice as much methane as the EPA had estimated there would be, suggesting a lot more methane than previously thought was leaking during extraction.

NOAA’s findings lent support to an earlier study, by Cornell researchers Robert Howarth and Anthony Ingraffea, who found natural gas to be no cleaner than coal when you factor in methane leakage. But that study was heavily criticized by the gas industry and other Cornell researchers, who contended the estimates of methane leakage were too high. The EPA stepped into the debate in April when it issued air pollution standards that will force producers to reduce methane leakage caused by fracking by 25 percent.

Figuring out the net effect on climate change of natural gas, and how that compares to other fuel sources, is complicated. Methane is more effective at trapping heat than carbon dioxide, the greenhouse gas most prevalent in the burning of coal and liquid transport fuels. But the methane doesn’t persist in the atmosphere as long.

That means, according to Alvarez, the methane emitted from powering a fleet of natural gas driven vehicles, for example, only presents a climate benefit over a gasoline-powered fleet after about 40 years. By his calculations, methane leakage would have to be cut by at least twice as much as the new EPA mandate for natural gas to become less harmful to the climate than gas or diesel in the short term. Compared to coal, though, he found climate benefits are immediate and increase over time.

Those figures, however, are based on the EPA’s official estimate that 2.4 percent of natural gas leaks out during production. When Alvarez and his co-authors ran their model using the median estimate from the Cornell study, 7 percent, natural gas for vehicle transport offers no benefits for at least 100 years. Compared to coal, natural gas would take 30 to 60 years to offer a benefit.

All of that may still seem to give natural gas the advantage. Not so, says James E. Hansen, the physicist who heads NASA’s Goddard Institute for Space Studies and is one of the earliest and most credible authorities to sound the alarm over global warming.

“If we reduce carbon dioxide emissions six percent a year starting in 2015,” he says, “we’ll level out at 350 parts per million of carbon dioxide in the atmosphere in about 2100.” Hansen and others believe 350 parts per million is the maximum amount of carbon dioxide the atmosphere can sustain for long periods without warming a disastrous 2º Celsius. The last time the planet was that warm—three million years ago—primates left Europe, alligators moved in, and the ocean was 25 meters above current levels--which would put Calcutta, Miami, and much of New York and Tokyo under water.

But even if we start bringing carbon dioxide levels down in the coming years, we may find ourselves in even worse shape if we accomplish it by switching wholesale to natural gas and releasing huge amounts of methane in the process. In the fight against climate change, Hansen maintains, time is one thing we don’t have.