The proposed rule, expected Friday from the Environmental Protection Agency, won’t cut any carbon immediately and won’t come anywhere near the sweeping mandate of the cap-and-trade plan that died in the Senate three years ago. But it will force the first-ever limits on greenhouse gas pollution from yet-to-be-built power plants, requiring costly carbon-cutting technology for those that burn coal.

The White House-vetted proposal is also the legal precursor to a far more ambitious draft regulation due next year that would seek cuts to climate-changing emissions at existing power plants. …

That’s if everything goes right for the administration: If the EPA rules aren’t weakened or killed in court. If Congress or a future Republican president doesn’t roll them back. And if it’s not too late to head off the worst effects of the rising seas and worsening droughts that climate scientists warn are already starting to ravage large swaths of the planet.

It’s a long game that is likely to bridge multiple presidencies. Experts have said the rules may not start reducing power plants’ emissions until 2018.