Natural gas has been widely hailed as a cleaner alternative to fossil fuels, but a new study by Cornell University researchers suggests it's not as green as many people think. Using hyped, unconventional sources of natural gas, such as that extracted from shale formations, say researchers, could do more to heat up the planet than mining and burning coal. Does natural gas really deserve its green reputation? A brief guide:

Doesn't natural gas burn cleaner than coal?
Absolutely. Researchers don't dispute that burning natural gas is cleaner than burning other fossil fuels. Natural gas emits 30 percent less carbon dioxide than oil, according to the Union of Concerned Scientists, and 43 percent less than coal. The problem with natural gas — particularly unconventional shale-gas extraction — comes before it even gets to the power plant.

How so?
Huge amounts of methane, the chief component of natural gas, escape when the fuel is pulled from the ground. To tap previously inaccessible pockets of gas trapped in shale deposits, energy companies use hydraulic-fracturing, or "fracking" — a high-pressure injection of water, sand, and chemicals — to break up the shale and free the gas. In the process, researchers say, as much as 7.9 percent of the underground methane seeps out or is intentionally vented.

Is that really so bad?
Cornell's scientists say methane is a much more powerful greenhouse gas than carbon dioxide and that "the footprint for shale gas is greater than that for conventional gas or oil when viewed on any time horizon."

Does the natural gas industry buy these numbers?
No. Natural gas producers say the Cornell study relies on data that even the researchers themselves have conceded is incomplete. Industry executives point out that if they let 7.9 percent of shale gas simply float into the atmosphere, they would be losing $6 billion a year. "These are huge numbers," says Range Resources' Mark D. Whitley, as quoted in The New York Times. "That the industry would let what amounts to trillions of cubic feet of gas get away from us doesn't make any sense. That's not the business that we're in."

Sources: The Atlantic, Fast Company, NY Times, Mother Nature Network