THIS WASN’T THE dramatic news that opponents of the Environmental Protection Agency (EPA) were hoping for: Last Tuesday, the Supreme Court declined to consider a variety of challenges to the EPA’s effort to slash greenhouse gas emissions.

But the news wasn’t a total victory for environmentalists. The court announced it would hear one challenge to the agency’s regulations: The Justice Department will have to convince the court that the EPA has the power under the Clean Air Act to put carbon-dioxide limits on so-called stationary sources — power plants, cement mixers and the like — using a powerful permitting program. If the court disagrees, it could rip some teeth out of the agency’s greenhouse gas effort.

Congress passed the Clean Air Act in the 1970s, when the air pollutants of concern were substances such as lead or particulate matter. Lawmakers wrote the law broadly, with the intent to regulate a variety of known and then-unknown pollutants. But the law’s language doesn’t fit perfectly when applied to carbon dioxide and other greenhouse gases, in part because virtually everyone and everything produces carbon dioxide.

The high court sorted through some of the confusion in 2007 with its landmark Mass. v. EPA decision, in which it confirmed that greenhouse gases are pollutants for the purposes of the Clean Air Act. Following that, the EPA set fuel-efficiency standards on cars and light trucks. Then the agency announced it would begin to regulate stationary sources, which would cut down on the amount of dirty coal burned. The justices on Tuesday refused to reconsider their 2007 ruling and let stand the regulations on vehicles. But they agreed to hear arguments against a piece of the EPA’s move to regulate power plants.

Opponents argue that, since applying every word of the law to greenhouse gas emissions immediately would produce “absurd” results, Congress never could have intended that there be a permitting program, which obliges big polluters to get special permits and install pollution-control technology. The government argues that the EPA’s job is to apply the law to greenhouse emissions as far and as fast as the agency reasonably can. A recent Supreme Court ruling found that the government has a coherent greenhouse gas policy in place, which indicates that the Obama administration stands a good shot at defending its right to pursue that policy. But the justices could have simply let lower court rulings stand; a pro-EPA outcome is far from guaranteed.

The overriding problem is that Congress hasn’t faced up to the global-warming threat. Instead of updating clean air rules and building a policy that addresses the unique challenge of greenhouse emissions, it has left the EPA and the courts with a strong but sometimes ambiguous law that applies imperfectly to greenhouse emissions. In the absence of congressional action, the EPA’s approach — interpreting the confusing text of the Clean Air Act in light of its overriding purpose to combat threatening air pollution — is the right one.