Who can sue to force the EPA to regulate greenhouse gases?

Here's the Linda Greenhouse account of yesterday's oral argument in the global warming case, Massachusetts v. Environmental Protection Agency:

“You have to show the harm is imminent,” Justice Scalia instructed [General James R. Milkey, representing the various states, cities and environmental groups who sued], asking, “I mean, when is the cataclysm?”

Mr. Milkey replied, “It’s not so much a cataclysm as ongoing harm,” arguing that Massachusetts, New York, and other coastal states faced losing “sovereign territory” to rising sea levels. “So the harm is already occurring,” he said. “It is ongoing, and it will happen well into the future.”

Chief Justice Roberts and Justice Alito both suggested that because motor vehicles account for only about 6 percent of carbon dioxide emissions, even aggressive federal regulation would not be great enough to make a difference, another requirement of the standing doctrine.

When Mr. Milkey replied that over time, “even small reductions can be significant,” Chief Justice Roberts responded: “That assumes everything else is going to remain constant, though, right? It assumes there isn’t going to be a greater contribution of greenhouse gases from economic development in China and other places that’s going to displace whatever marginal benefit you get here.” At another point, the chief justice said the plaintiffs’ evidence “strikes me as sort of spitting out conjecture on conjecture.”

In other words, even if you think the injury is enough for standing, there are problems on the "causation" and "redressability" prongs on the standing doctrine. Don't be distracted by Scalia's wondering about the "cataclysm." You can assume for the sake of argument that the plaintiffs face injury and still find no standing, for the sole reason that the relief they are seeking isn't likely enough to change the situation. But, looking at the transcript, I see they did focus more strongly on the injury question. Back to Greenhouse:

On the other side, Justices Stephen G. Breyer, Ruth Bader Ginsburg, John Paul Stevens and David H. Souter appeared strongly inclined to find that the plaintiffs had met the standing test.

They generally do apply standing doctrine less strictly... which means that Justice Kennedy is the swing voter.

[Kennedy's] relatively few comments were ambiguous. Early in the argument he challenged the assertion by Mr. Milkey, the states’ lawyer, that the case “turns on ordinary principles of statutory interpretation and administrative law” and that there was no need for the court “to pass judgment on the science of climate change.”

That was “reassuring,” Justice Kennedy said. But, he added, “Don’t we have to do that in order to decide the standing argument, because there’s no injury if there’s not global warming?”