By: The New York Times Editorial Board

In eight years, President Obama has established a strong record in fighting climate change, including ambitious fuel efficiency standards aimed at reducing carbon dioxide emissions from cars and trucks.

But one very important part of his strategy remains in legal limbo — the Clean Power Plan, a rule created by the Environmental Protection Agency that would place strict limits on carbon dioxide emissions from coal- and gas-fired power plants and would force many of the dirtiest to shut down.

The rule orders states to make big cuts in carbon dioxide emissions from power plants over the next 15 years, setting individual goals for each state while giving them considerable flexibility in how to get reach them. This framework is wholly consistent with the federal-state partnerships that for years have governed the nation’s environmental statutes.

On Tuesday, however, 28 states, scores of power companies and industry groups were before the Court of Appeals for the District of Columbia to challenge the E.P.A.’s authority to use this approach under the Clean Air Act, on which the rule is based. Opposing them were 18 states that support the rule and dozens of environmental and public interest groups, as well as the Obama administration.

There is no question that the Clean Air Act allows the federal government to regulate carbon dioxide emissions; the Supreme Court has said it does. And there’s no question that the government can regulate these emissions from power plants; the Supreme Court has said so.

The issue is whether the E.P.A. can use an approach to regulating greenhouse gases, different from the way it has regulated other types of pollutants, like mercury emissions. Traditionally, in reducing those pollutants, the agency has required power plants to make technological improvements. But no economically feasible technology is yet available to control carbon dioxide emissions at the plant level.

The agency has therefore told the states that to meet their targets they must move “outside the fenceline” of existing power plants by, say, switching to cleaner fuels, investing in alternative forms of energy like wind and solar power and setting up cap-and-trade systems with other states. Opponents say this is a prime example of “executive overreach.” But this pragmatic strategy is entirely consistent with the Clean Air Act’s fundamental mandate to seek “the best system of emission reduction.”

Of the court’s 10 judges, six are Democratic appointees, which gives the rule a good chance of surviving, as it should. Despite apocalyptic warnings from some of the opponents that the rule would destroy America’s energy system, it would in fact move that system in the same direction that the marketplace and modern technology are already driving it — toward cleaner energy alternatives, and away from the oldest and dirtiest fossil fuels.

The opponents also offer other objections, including a long-forgotten legislative glitch that occurred when Congress amended the Clean Air Act in 1990. The House version of the legislation said the agency could not regulate a new pollutant under one section of the law (the one it is relying on now) if it were already regulating other pollutants under another section. The Senate, in effect, said that such overlapping regulation was fine. The argument that this clerical discrepancy should keep the agency from regulating carbon dioxide is preposterous.