Natural gas is often considered the cleanest fossil fuel, but could it actually be dirtier than coal?

Watch as New York Times reporter Mark Bittman, in the above Year's of Living Dangerously video, investigates how much methane is leaking at fracking wells. Find out how the natural gas industry's claims compare to what scientists are reporting.

See what happens when Gaby Petron, an atmospheric scientist with NOAA, converts her van into a mobile methane detector and sets out across northeastern Colorado for two years, taking thousands of readings to uncover the truth.