Environmental Protection Agency Administrator Scott Pruitt could help the U.S. make a significant dent in emissions of carbon dioxide if he were to start a sincere effort to replace the Obama-era Clean Power Plan with a more modest regulation, experts say.

"The EPA in a serious effort has plenty of tools to gather information on how power plants operate, analyze that information and identify ways that significant emissions reductions could be mandated on site," said Joe Goffman, a chief architect of the Clean Power Plan who was the lead attorney at the EPA when the Obama administration created the rule in 2015. "You could tee up a lot of options, including ones that are aggressive."

But experts doubt how committed Pruitt is to establishing his own regulation mandating emissions limits on coal and natural gas plants, predicting he may try to slow-walk the rulemaking process so he never has to sign something that conflicts with his political interests. Pruitt, as Oklahoma's attorney general, sued the federal government more than a dozen times, including over the Clean Power Plan, which requires states to reduce carbon emissions by 32 percent below 2005 levels by 2030.

"Scott Pruitt loves coal, and Donald Trump loves coal, and they will do everything possible to leave coal alone and not regulate it at all," said David Bookbinder, chief counsel at the libertarian Niskanen Center and former chief climate counsel at the Sierra Club. "The longer the EPA does nothing about a problem that is blindly obvious and has worse and worse consequences, the more likely courts step in and make them do something. And I think Pruitt has just taken one big step down that road."

Even the fiercest critics of the Clean Power Plan say Pruitt may have no choice but to act because the EPA is bound to regulate emissions of carbon and other greenhouse gas under a 2009 agency rule known as the endangerment finding.

"I am not a lawyer, but lawyers have made that argument quite a few times, and I listen to it," said Myron Ebell of the free-market Competitive Enterprise Institute, who led President Trump's EPA transition team. "They will need some replacement."

Pruitt in announcing his intent to repeal the Clean Power Plan this week said the Obama administration had exceeded its legal authority in creating the Clean Power Plan, the centerpiece of former President Barack Obama's plan to battle climate change. Many climate scientists blame greenhouse gases from burning fossil fuels such as coal and crude oil for driving manmade climate change.

"The war on coal is over," Pruitt declared Monday, announcing the repeal at a coal equipment supply company in Hazard, Ky.

The Trump administration says Obama based the Clean Power Plan on an expansive and illegal interpretation of the Clean Air Act. The Clean Power Plan was the main U.S. pledge as part of the international Paris climate change agreement, which the Trump administration intends to leave.

The Clean Power Plan was never implemented, because it was stayed by the Supreme Court in February 2016 while legal challenges worked their way through the courts.

Under the rule, the EPA gave each state a goal for reducing emissions and encouraged broad ways to meet those targets, such as moving away from coal to natural gas, and transitioning to wind and solar power. The power plan interpreted the Clean Air Act in a way that allowed it to regulate power plants outside the "fenceline" of the facilities themselves, while including renewable energy and energy efficiency standards, which was one of the legal challenges against it.

Pruitt told the Washington Examiner in interview last month that he would seek to regulate power plants individually, in a process known as "inside the fenceline." For example, the EPA could mandate heat rate improvements in power plants, which would burn coal more efficiently by creating more electricity per unit of coal.

Goffman said the Obama administration took a more holistic view because it was more cost-effective and what the utility industry and others preferred.

But he said the EPA could achieve emissions reductions of about 5 percent if it strictly focused on efficiency improvements inside power plants and potentially double that if the agency encouraged the adoption of carbon capture and storage technology.

"If I were in the utility industry, I would not assume that a replacement rule that relied only on within the fenceline would be merely a modest rule," Goffman said.

Carbon capture and storage, known as CCS, removes carbon dioxide from a power plant's exhaust, so as to not release it into the atmosphere and contribute to global warming. The carbon can be cooled and injected as a liquid underground.

"You could make enormous reductions within the fenceline by requiring carbon capture and storage," said Richard Revesz, an environmental law professor at New York University. "It would run coal out of the market."

Others say CCS technology is too expensive to enforce power plants to adopt it.

Ebell predicts that an EPA regulation focused on individual power plants would have a more modest impact on emissions. He argues the Clean Air Act grants the executive branch limited authority to make a meaningful carbon regulation.

"What [the Trump administration] will try to do is say, yes, we will abide by the letter of the law and regulate greenhouse gas emissions using the tools the Clean Air Act has allowed for in regulating individual power plants," Ebell said. "Doing what's in the boundaries of the law turns out to be very modest."

Ebell contends only Congress can create stronger policy.

"If the American public really wanted greenhouse gas emission reductions, it's up to Congress to do that effectively, instead of the executive branch rigging the Clean Air Act so you get something," Ebell said.

The repeal plan introduced by the Trump administration could take months to implement.

Separately, the EPA said it would ask the public for ideas on how to replace the Clean Power Plan.

In the next few weeks, the agency will issue an advance notice of proposed rule making that sets forward the public comment process before issuing a new regulation.

Jeff Holmstead, a former deputy administrator of the EPA in the George W. Bush administration, predicts Pruitt will propose a new rule in the next five to six months. But he conceded the process could be delayed because few EPA political appointees have been confirmed, leaving the agency short-staffed.

Holmstead says business groups would welcome a more limited regulation. The Trump administration would be sued if it did nothing, he added.

"It is clear the EPA has an obligation to regulate CO2 emissions from existing plants," said Holmstead, who is now an energy lobbyist at Bracewell LLP. "The vast majority of folks in the business community would like to work with the EPA on a reasonable regulation."

Holmstead insists Pruitt can create a regulation that mandates power plant efficiency improvements to transition coal to a cleaner future, without killing coal.

"I don't think anybody believes that we're going to see coal-fired generation disappear anytime in the foreseeable future, even with the relative low prices of natural gas and renewables," Holmstead said. "The question is a good one: Can you regulate coal plants if your hope is to save them? And the answer is, yes, if you do that regulation in an appropriate way."

The U.S. is more than halfway toward meeting the Clean Power Plan's emissions reductions goals even though it never took effect.

Many companies and states are moving away from coal, opting for cheaper natural gas or renewable power because it makes economic sense to do so.

Revesz expects that progress to continue, no matter what the Trump administration does.

"It's clear this replacement is at a very slow timeline," Revesz said. "The bottom line is this issue won't get resolved until the end of this presidential term. In the meantime, we are ahead of schedule. We are making good progress because of market forces."