That’s the report in which the agency concluded that climate pollution endangers public health and welfare and thus must be regulated under the Clean Air Act. It’s the basis of all federal climate regulations.

As I wrote back in August when the EPA released its draft proposal, the agency has now – over a decade and a half later – reinterpreted the Clean Air Act to only apply to direct health impacts from local pollution, and not to indirect health effects, like those associated with global climate pollutants.

The agency finalized the decision six months later. And the EPA has already been rolling back all of its climate regulations.

It’s worth bearing in mind that while EPA regulations could be effective at reducing climate pollution, in practice, they haven’t done a whole lot. That’s because EPA regulations tend to swing back and forth every time a new political party takes control of the White House.

Vehicle tailpipe standards are the only significant climate-related regulation that’s gone into effect, and even those overlapped with separate vehicle fuel efficiency standards – which are also now being rolled back. Overall, nearly all of the United States’ emissions reductions have come from the power sector, but that’s because cleaner sources of electricity became cheaper than coal, not because of EPA regulations.

What’s next?

So what happens next is that various groups will sue the EPA, and the case will ultimately be appealed up to the Supreme Court in a process that will likely take several years. At that point, there will be three possible outcomes.

In a best-case scenario, the Supreme Court could rule that the EPA is wrong and must regulate climate pollution under the Clean Air Act. That would require the agency to reissue a broad swath of climate pollutant regulations in the ensuing years.

In a middle scenario, they could narrowly rule in favor of the EPA, giving the agency the discretion to decide whether to regulate climate pollutants. That would maintain the status quo of regulatory swings whenever a new party wins control of the White House.

In the worst-case scenario, the Supreme Court could rule that the EPA is correct in its interpretation that the agency doesn’t have the authority to regulate climate pollutants under the Clean Air Act. That would tie future administrations’ hands on climate regulations. That could also leave fossil fuel companies liable to state-level lawsuits. They were shielded from those by the existence of federal climate regulations.

In that case, or at least in the meantime, that leaves American climate policy almost exclusively in the hands of Congress and individual states.