The Trump administration's decision to terminate its predecessor's Clean Power Plan, accomplished via an executive order, would seem to be a carefully crafted decision with an air of finality about it. It neatly avoided rejecting mainstream climate science, opting instead to eliminate the only federal plan for doing anything about it.

The reality is far more complex. Unlike other actions by the Obama administration, which occurred late in his second term, the Clean Power Plan had gone through the entire federal rulemaking process. To get rid of it, the process has to be repeated in its entirety. And the scientific document that formed the foundation for the Clean Power Plan won't be touched by the reversal. Its existence is likely to leave the Trump EPA in a legally awkward position, one where they'll have to come up with some regulation to tackle climate change.

Making and breaking the rules

While federal regulatory actions can often seem arbitrary, they're the result of a highly formalized process. To begin with, they're grounded in some regulatory activity that Congress has delegated to the executive branch. For example, it would be unreasonable to expect that Congress could pass individual laws to ensure the safety of every chemical humans might be exposed to. Instead, Congress has determined under which circumstances regulatory agencies can act on a chemical and provided guidelines on what those actions can entail.

These actions have to undergo a formalized rulemaking process, laid out by Congress in the Administrative Procedure Act. This includes publishing draft rules, receiving and addressing public and stakeholder comments, finalizing the rules, and publishing them in the Federal Register. It's a process that can often take years—before the lawsuits start.

Once a rule has been through that entire process, as the Clean Power Plan has, the only way to get rid of it is to go through the whole thing again. "The whole process of repealing regulations is complex," said David Doniger of the Natural Resources Defense Council, an environmental organization. "You have to tear the building down the same way you built it up." That means the same process of building a case for doing so, submitting it for public comment, revising it, and so on.

Once finalized, the government can be sued over the rules that were eliminated. "At the end of that process, you've gotta go to court," Doniger told Ars. "Groups like ours that support these rules, industries that support these rules, will challenge the repeal."

Trump's executive order, rather than getting rid of the Clean Power Plan, only directs the EPA to begin the process of doing so. If that process is interrupted at any point or the results are rejected during the legal proceedings that will inevitably follow, then the Clean Power Plan would remain in place as part of federal regulation by default.

You've got to do something

Even if Trump's EPA can get all of that done, it still won't be done dealing with greenhouse gas regulations. That's because the Clean Power Plan was a product of the Clean Air Act, which has some very specific expectations about how pollutants are handled. The process starts with what's called an Endangerment Finding, in which the EPA evaluates the available data and determines that a pollutant poses a risk to public health or welfare. And, once that determination is made, then the government has to do something about it.

"Once the EPA has made the scientific determination that a pollutant endangers public health or welfare," Doniger said, "then there are legal obligations to regulate the pollution." That regulation is source-based—the EPA identifies different sources of the pollutant and analyzes each. "You go right down the list of all the potential sources of these gases," said Pat Parenteau of the Vermont Law School. "And each time you consider one of these source categories, you have to make [a] cause or contribute finding."

If a source causes or contributes to the problem, it has to be regulated. "The administrator of the EPA must act to regulate the sources of those gases that cause or contribute to the endangerment," Parenteau told Ars. In response to its endangerment finding, for example, the Obama administration had negotiated an agreement with automakers to improve fuel efficiency (also in the process of being eliminated). That administration formulated the Clean Power Plan for electricity generation, and the process for aircraft emissions was also started.

If those pollutants have already been named following an endangerment finding, they have to be regulated. "They're under legal obligation to replace [existing regulations] with something," Doniger said. "You can't repeal without replace." Plus, Doniger said there's a time limit: "When you've listed a type of source as emitting a dangerous pollutant, you have a year to propose standards for it. And then you have another year to do the rulemaking process."

This leaves the Trump administration with two options for dealing with the process that the Obama administration set in motion. If we assume its goal is to eliminate regulation of greenhouse gases, both options are bad.