NY, 6 other states suing EPA over drilling methane

Overall, EPA says that methane is responsible for 3.8 percent of the total greenhouse gas emissions in the United States. Other major greenhouse gases are carbon dioxide, nitrous oxide and ozone. Methane is a more potent greenhouse gas than carbon dioxide, but it also decays much quicker.

Patrick Henderson, Pennsylvania's energy executive in Gov. Tom Corbett's office, noted that other top New York officials have recently supported more natural gas use.

"Gov. Cuomo proposed investing $500 million in natural gas distribution infrastructure, and New York City Mayor Bloomberg wrote in a Washington Post op-ed that shale gas 'is one of the best things we can do to improve air quality and fight climate change,'" Henderson said in an email.

Henderson added that natural gas also has environmental benefits, since it emits just 50 percent of the carbon dioxide of coal-fired power plants. That switch from coal to gas has contributed to declining greenhouse gas emissions in the U.S., according to federal energy statistics. He also noted that increased domestic oil and gas production has helped reduce imports.

Federal climate researchers say they haven't yet seen signs that increased drilling is affecting global methane levels, but they're worried about the threat.

"Not the mid-latitudes where the drilling is being done, which is interesting," said James Butler, head of global monitoring for NOAA. Butler said the tropics and the arctic are the biggest current sources, from decaying vegetation (linked to a rise in rainfall) and thawing of the Arctic tundra (linked to global warming).