After a cursory read of the complex, 645-page rule, New Jersey officials initially declared victory. They had already met the state's 2030 target, they said.
Then, they weren't so sure.
They began seeing inconsistencies and ambiguities in some of the information the EPA provided. "It has some of our experts here confounded," said Bob Marshall, assistant commissioner for sustainability and green energy with the state Department of Environmental Protection.
Either way, he said, "New Jersey's got a good story to tell. We have one of the cleanest power sectors in the country, and one of the lowest carbon dioxide emission rates."
The Sierra Club's New Jersey chapter director, Jeff Tittel, said the state can - and should - do more, especially given its vulnerability to rising sea levels, stronger storms, and other effects of climate change.
A fact sheet on the EPA's website showed that New Jersey's 2012 emission rate was 932 pounds of carbon dioxide per megawatt hour of electricity generated. The proposed target is 531 pounds.
Pennsylvania's 2012 rate was 1,540 pounds. The proposed target is 1,052.
Gov. Corbett expressed concerns that the new mandate - the latest in a series of EPA actions to limit pollutants from coal-fired power plants - would force plant closures and destroy jobs.
He said Pennsylvania is already doing its "fair share to reduce carbon emissions, and we have made great strides in recent years."
Still, Jake Smeltz, president of the Electric Power Generation Association, a Pennsylvania industry group, concluded from his initial read that the rule appears "workable."
"The commonwealth will be in a position to write its plan and take into consideration the things that are unique to our state," Smeltz said.
Such as: Pennsylvania ranks fourth in the nation in coal production and No. 2 in the production of electricity - mostly from coal, although nuclear and natural gas are not far behind.
He said it was helpful that the EPA would allow "outside the fence" compliance options - such as renewables and energy efficiency - to take the pressure off coal-fired plants.
The time frame - giving states 15 years to fully comply - also is a plus, he said. "It appears to take into consideration what we call the natural life of a power plant," leading to a much more natural transition of the energy landscape.
Exelon Corp., owner of several nuclear power plants in Pennsylvania and New Jersey, said in a statement, "We are pleased that the draft rule recognizes the critical importance of supporting the continued operation of the nation's nuclear fleet."
Environmental leaders in both states said they hoped to see more emphasis on renewable energy such as solar and wind, and more energy efficiency efforts in homes and businesses, which would cut electricity bills, also.
However, they, too, cautioned that it's early in the game. "We're all going to have to sift through a lot of materials, a lot of briefings," said Joseph O. Minott, executive director of the Clean Air Council, a Pennsylvania nonprofit.
He was critical of a state DEP white paper released in April that included waste coal and waste-to-energy facilities among possible ways to meet the state's target.
"It's not forward-thinking. It's not cutting-edge. It's not job-creating," Minott said. "Every report that I have read suggests that investments in energy efficiency and alternative energy are incredibly cost-effective. They stimulate the economy. They create jobs that can't be exported."
Promoting a menu of low-carbon sources of power will "allow Pennsylvania and the regulated communities to reduce emissions and comply with this rule in the most economically way possible," said Christina Simeone, director of the energy center at PennFuture, a state environmental group.
Natural gas is viewed as a lower-carbon alternative, and already some coal plants have announced plans to switch. But the reductions in carbon emissions at the plants could be offset by emissions of methane, a more potent greenhouse gas, at natural gas production and distribution facilities, she and others said.
If that happens, "we will not win" the overall goal of addressing climate change, Simeone said.
In advance of federal methane rules, "there's so much the state can do to reduce this . . . and unleash the potential of natural gas to be more of a solution rather than an unknown," she said.
The EPA is holding a 120-day public comment period, with hearings in Denver, Atlanta, Pittsburgh, and Washington. It plans to issue a final rule by June 2015. State plans are due in June 2016.
In announcing the proposed rule, EPA administrator Gina McCarthy said it would protect not only the environment but public health. The agency estimates that as many as 6,600 premature deaths and 150,000 asthma attacks could be avoided every year.