Set to be killed by Trump, the rules mostly lock in existing trends. //

The net result of a number of Supreme Court decisions is that greenhouse gasses are pollutants under the Clean Air Act, and the EPA needed to determine whether they posed a threat to people. George W. Bush's EPA dutifully performed that analysis but sat on the results until its second term ended, leaving it to the Obama administration to reach the same conclusion. The EPA went on to formulate rules for limiting carbon emissions on a state-by-state basis, but these were rapidly made irrelevant because renewable power and natural gas began displacing coal even without the EPA's encouragement.

Nevertheless, the Trump administration replaced those rules with ones designed to accomplish even less, which were thrown out by a court just before Biden's inauguration. Meanwhile, the Supreme Court stepped in to rule on the now-even-more-irrelevant Obama rules, determining that the EPA could only regulate carbon emissions at the level of individual power plants rather than at the level of the grid.

All of that set the stage for the latest EPA rules, which were formulated by the Biden administration's EPA. Forced by the court to regulate individual power plants, the EPA allowed coal plants that were set to retire within the decade to continue to operate as they have. Anything that would remain operational longer would need to either switch fuels or install carbon capture equipment. Similarly, natural gas plants were regulated based on how frequently they were operational; those that ran less than 40 percent of the time could face significant new regulations. More than that, and they'd have to capture carbon or burn a fuel mixture that is primarily hydrogen produced without carbon emissions.