Everyone says the recent Clean Air Act victory in the Supremes was a 'rare EPA success' and an equally rare defeat to the US Chamber of Commerce. Not too surprising given that the Court hasn't had an environmentalist serving on it since William Douglas left in 1975, while big corporate lawyers abound as justices.
The full decision is here, a good and brief writeup here. Some comments I've seen suggest it bodes well for more direct regulation of greenhouse gases. My first reaction was probably not, my second reaction is more hopeful.
The decision is about coal (mostly) pollution crossing state lines. Rather than the EPA beating up private industry, it's about the federal government playing an umpire role between states. Justice Kennedy makes a big deal about the important role of the states, so here he may have seen the EPA make sure states play nice with each other. Greenhouse gas regulation won't be seen in the same terms of protecting sovereign states from impacts across their borders.
On the other hand, EPA used a fairly liberal interpretation of its ability to protect against cross-border pollution that made the rule less onerous by applying a cost-benefit analysis. Opponents tried to make the law's required application so difficult that it wouldn't even be attempted, or at least delayed for years - a trick they've tried previously on Obamacare and greenhouse gases. Being flexible in order to make the law workable is a useful precedent here.
And of course this is one more thing making it hard for dirty coal plants to keep polluting. One more step in the right direction.