Of all 3 issues in which the DC Ct ruled for EPA, this is the only one that SCOTUS agreed to hear on appeal. They rejected the other 2.
The Supreme Court considered nine petitions seeking review of the appeals court’s decision on many grounds, and it accepted six of them. But it limited the issue it would consider to whether the agency “permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouses gases.” Among the cases accepted for review was Utility Air Regulatory Group v. Environmental Protection Agency, No. 12-1146.
The question was narrow, and it appeared spurred by Judge Kavanaugh’s dissent. Environmental groups said they were pleased that the court had not questioned the agency’s finding that greenhouse gases pose a danger, or that it can regulate tailpipe emissions. They added that the agency has other tools to regulate stationary sources should it lose in the pending case.
From this article:
As Obama Vows to Act on Climate Change, Justices Weigh His Approach
Earlier in the article:
When the full appeals court declined to rehear the case, Judge Brett M. Kavanaugh dissented, and he identified the ground that would turn out to interest the Supreme Court. He said the agency had gone astray in revising the text of the statute.
“The task of dealing with global warming is urgent and important,” Judge Kavanaugh wrote, but it is primarily one for Congress to address. “The framers of the Constitution,” he added, “did not grant the executive branch the authority to set economic and social policy as it sees fit.”