Leaking natural gas equipment is one of the reasons it's a more polluting fossil fuel than coal.

Touted as a "clean-burning" fuel that will wean Americans off dirty coal and imported oil, natural gas is turning out to be no bargain for the environment.

The Environmental Protection Agency (EPA) just released its most recent statistics on greenhouse-gas emissions, and pegged natural gas production, storage, and transportation as the second-highest source of greenhouse-gas emissions in the United States.

Although it's true that natural gas emits very few greenhouse gases while it's being burned, it seems the other aspects of its life cycle aren't quite so climate friendly. The EPA calculated the emissions from both the burning of natural gas and leaks from pipelines and the drilling process known as hydraulic fracturing, or fracking, in which water, sand, and chemicals are injected underground to fracture shale rock. Combined, natural-gas production and distribution accounted for 225 million metric tons of greenhouse gases, second only to power plants.

This isn't news to Richard Howarth, PhD, David R. Atkinson Professor of Ecology and Environmental Biology at Cornell University. In 2011, Howarth did a life-cycle analysis of the greenhouse-gas emissions associated with both using and drilling for natural gas, and found that leaky gas wells caused this so-called "clean-burning fuel" to emit 1.2 to 2.1 times more greenhouse gases than coal did over a 20-year time period. The problem is with methane, a greenhouse gas 23 times more potent than carbon dioxide. Natural gas is predominantly methane, and in the process of bringing it up from underground, leaky equipment and natural cracks in the wells created by fracking allow methane to leak and escape into the atmosphere.

"There's more new science coming out this year in journals and at various meetings showing that the amount of methane that's leaked from gas is even higher than we had estimated," he says. Recent studies have suggested that as much as 9 percent of the methane leaked from natural gas sites escapes this way.

The EPA has already used greenhouse-gas data from its last report to put emissions limits on power plants, but the agency hasn't done anything to address methane leaks from natural-gas fracking sites. International governments, on the other hand, are using EPA's data to set methane limits in their own countries. "The latest science from the UN Environment Programme has led to the UN saying we need to get methane under control right away," says Howarth, "or else we'll reach the tipping points for climate change in the next decade or so."

Methane persists in the atmosphere for 20 years, a shorter time than other greenhouse gases like carbon dioxide do, but it's more efficient at trapping radiation and heat, making it a far more damaging pollutant.