Connecticut and six other Northeastern and mid-Atlantic states unveiled plans last week to sue the Environmental Protection Agency, saying it is violating the Clean Air Act by failing to address methane gas emissions from oil and gas drilling, which has boomed in nearby states such as Pennsylvania and West Virginia.

“EPA has determined that emissions of this potent greenhouse gas endanger public health and welfare, and that processes and equipment in the oil and gas sector emit vast quantities of methane,” state Attorney General Jepsen said in a statement. “Yet the EPA failed to set standards and guidelines limiting methane emissions from oil and gas operations.

State Department Energy and Environmental Protection Commissioner Daniel C. Esty said domestic natural gas reserves offer a “very real and important opportunity” to make cleaner, cheaper energy available to residents and businesses. But he said, “we must take advantage of this valuable resource in an environmentally responsible manner – and that means strong regulatory oversight of methane emissions by EPA.”

Pound for pound, methane warms the climate about 25 times more than carbon dioxide, the Connecticut officials claimed. EPA has found that the impacts of climate change caused by methane include “increased air and ocean temperatures, changes in precipitation patterns, melting and thawing of global glaciers and ice, increasingly severe weather events, such as hurricanes of greater intensity and sea-level rise.”

This is the second major climate change case that the state of Connecticut has been involved with in recent years. In 2004, it was one of the named parties in a lawsuit that evolved into American Electric Power Company Inc. v. Connecticut, which pitted five major power companies and the federally run Tennessee Valley Authority against a group of states that want to limit coal-fired power plant emissions.

The states alleged that the utilities are the largest emitters of greenhouse gases in the U.S., and that those gasses trap atmospheric heat and cause global climate change, which is an ongoing public nuisance that must be abated under federal or state common law.

The district court dismissed the states’ claims, ruling that the case raises a “political question” that can only be addressed by the legislative or executive branches. But in 2009, the U.S. Court of Appeals for the Second Circuit reversed the district court and reinstated the lawsuit. It held that the political question doctrine does not bar the suit; that the states had constitutional standing to bring the case; and that plaintiffs had made a successful claim under the federal common-law doctrine of nuisance.

Then in 2011, the U.S. Supreme Court unanimously reversed the Second Circuit, holding that the Clean Air Act, and the authority it confers on the U.S. Environmental Protection Agency to regulate emissions of carbon dioxide and other greenhouse gases, “displaces” any federal common law right of state, municipal and private plaintiffs to assert tort claims in the federal courts.

As for the threatened methane lawsuit, the EPA said in an e-mail that it plans to review and respond to the notice from the states.

Howard Feldman, a spokesman for the American Petroleum Institute, said the lawsuit “makes no sense” since the EPA passed rules on oil and gas emissions earlier this year, and many companies have already started installing new equipment to limit methane leaks and other pollution. Those rules take effect in 2015.

Peter ZalZal, a staff attorney with the Environmental Defense Fund, said the group thinks the recent EPA rules are “a good first step,” but that more can be done to target methane emissions directly. “We think that controlling and reducing methane emissions from the oil and gas industry is critical,” ZalZal said.

New York Attorney General Eric T. Schneiderman said that the coalition of states “can’t continue to ignore the evidence of climate change or the catastrophic threat that unabated greenhouse gas pollution poses to our families, our communities and our economy.”

He said Connecticut, Delaware, Maryland, Massachusetts, Rhode Island and Vermont joined in sending a required 60-day notice of intent to sue to EPA. None of the states that sent the notice to the EPA are major producers of oil or gas.

Pennsylvania, West Virginia, and Ohio — all states with intensive oil and gas drilling — didn’t join in the campaign.

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. [Andrew] Cuomo proposed investing $500 million in natural gas distribution infrastructure, and New York City Mayor [Michale] 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 e-mail.

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). •