Natural gas pollutes much more at the electric generation site than previously thought.

At the electric generation site, it has been understood that burning coal spews vastly more CO2 into the atmosphere than natural gas. Most of the pollution for natural gas occurs at the extraction site, where much of it leaks into the atmosphere (plus the toxic brew of water used to extract it).

But now, it seems that natural gas does not burn as thoroughly as once thought.

http://www.theecologist.org/News/news_round_up/2988788/natural_gas_leaks_from_power_plants_refineries_100_times_greater_than_thought.html