What is the Clean Power Plan?
Upon signing it, Obama called it the "the biggest, most important step we have ever taken to combat climate change."
According to the EPA, the Clean Power Plan was designed with three building blocks. First, it required an increase in the efficiency of existing coal-fired power plants. Second, it moved electricity generation away from fossil fuel-fired, coal power plants to natural gas-fired power plants. And third, it planned to increase the use of renewable energy sources like wind and solar.
With the Clean Power Plan, each state was given specific carbon emission goal for electricity producers. The EPA claimed that the climate and health benefits of the plan "far outweigh the estimated annual costs of the plan, which are $7.3 billion to $8.8 billion in 2030." It also claimed that the plan would reduce asthma rates in adults and children.
But the Clean Power Plan isn't currently being enforced because the law is stuck in legal proceedings. On February 9, 2016, the Supreme Court stayed implementation of the law pending judicial review. Attorney generals from 28 states -- led by Pruitt, when he was Oklahoma's attorney general -- joined together to claim that the plan presents too broad an interpretation of the Clean Air Act.
In December, those state attorney generals wrote a letter to President Trump, Vice President Mike Pence, and Speaker of the House Paul Ryan urging them to withdraw from the Clean Power Plan on day one of the Trump administration, saying that the rule "directly intrudes on each state's traditional prerogative over its mix of electricity generation."
Legal challenges ahead
The first hurdle for the Trump administration will be moving Obama's rule out of the U.S. Court of Appeals for the District of Columbia Circuit where it currently stands in legal limbo.
The rewriting of the Clean Power Plan could take over a year, as it requires the EPA to follow the same procedure of rule-making used when crafting the original plan. This means, for every rule the EPA plans to rewrite, the administration will have to justify why the rule is being rolled back. Then, comments will be made on each of the new rules that the administration must respond to. This complex re-writing period will likely face hefty litigation from environmental advocacy groups opposed to the executive order.
The same year Obama signed into law the Clean Power Plan, the U.S. signed onto the Paris Climate Agreement.
The goal of the Paris deal is to commit countries worldwide to lowering the emission of greenhouse gasses. To remain in the deal, the U.S. must cut its emissions by about 26 percent from 2005 levels by the year 2025.
Exactly how the Clean Power Plan will affect the Paris Climate Agreement is "unknowable," Richard Lazarus, an environmental law professor at Harvard University, told ABC News.
"As a formal matter, we cannot really withdraw from Paris for about two years," said Lazarus. He added that China might welcome the withdrawal by the U.S, though, as it would provide the country with an opportunity to take leadership on a global issue and take the charge on clean technology innovations.
Rolling back the Clean Power Plan "affects our standing in the world as a leader in climate change issues and we'll have to see what the other countries do," he said.
Environmental advocacy groups and health organizations are roiling over Trump's executive order.
"With this executive order, the Trump administration is simply putting America further behind in the global race towards a renewable future," Greenpeace USA executive director Annie Leonard said in a statement.
Harold Wimmer, CEO of the American Lung Association, raised concerns about how the new order will affect air quality. "Today's executive order directly contradicts EPA's core mission of protecting public health and the environment, and undercuts the Agency's ability to achieve the promise of the Clean Air Act -– ensuring that all Americans are able to breathe clean, healthy air."
But the United States Chamber of Commerce came out in support of the Trump administration's plans. "America got good news today when President Trump took bold steps to make regulatory relief and energy security a top priority," the lobbying group said in a statement. "The U.S. Chamber has long argued that EPA's power plant regulations are not only unlawful, they are a bad deal for American families and businesses."