AFTER CONGRESS failed to pass a comprehensive climate change bill in 2010, the Obama administration shifted its approach to cutting greenhouse gas emissions. Instead of waiting for a fresh environmental law tailored to slashing carbon dioxide, the Environmental Protection Agency (EPA) would do as much as it could with the power the Clean Air Act gave it decades ago. The Supreme Court on Monday will hear arguments about just how much power that is.

The proceedings will focus on subtle interpretations of a handful of words in the act’s sprawling and difficult text. The task of the justices, though, is to defer to the fairest reading of Congress’s intent. On that, the EPA has a better case than the critics who want to defang it.

A lot has gone environmentalists’ way up to this point. The court ruled in 2007 that carbon dioxide qualifies as a pollutant under the act. The Obama EPA moved to restrict carbon emissions from car and truck tailpipes, regulations on which the court declined to hear challenges. Basic national standards on so-called stationary sources — think smokestacks rather than tailpipes — also seem destined to come into force. The big, outstanding question is whether the EPA can use some powerful permitting requirements in the Clean Air Act on those stationary sources.

Here’s the trouble: The act specifies that facilities emitting a certain amount of pollution should be subject to permits, but those threshold amounts don’t make sense when applied to greenhouse emissions. While only a major industrial facility could emit 250 tons of, say, sulfur dioxide a year, apartment buildings, hospitals and other commonplace facilities emit that amount of carbon dioxide each year — possibly subjecting all of them to EPA permitting. Congress, the EPA’s opponents argue, obviously couldn’t have meant for these portions of the act to apply to greenhouse emissions, so they shouldn’t. The government fires back that the EPA shaped its rules to apply the law as far and as fast as is practical, sensibly deciding to start with the largest carbon emitters first.

Surely that’s closer to what Congress desired when it passed the Clean Air Act, a comprehensive law designed to deal with a range of bona-fide air pollutants. The court should not render major portions of the law inapplicable simply because Congress decades ago didn’t anticipate the particular circumstances of the greenhouse gas threat. The court itself, the government notes, even recently held in a different case that the EPA’s greenhouse gas program represents a comprehensive federal climate change policy. That would hardly make sense if big, stationary emitters were exempt from the law’s front-line clean-air permitting rules.

However the court resolves this dispute, the real villains are clear: the last several Congresses. Instead of designing rules to deal with greenhouse gas emissions, lawmakers have dawdled while the EPA has done its best.