The Wall Street Journal speculates:
The ruling means the EPA must regulate automobile emissions unless that agency can show the science of global warming, or the potential harm it may cause, are too uncertain to justify action. The Bush EPA will no doubt be sued whatever it does. Congress will also dive in with more regulation, if only to clear up the legal uncertainty.Cato's Patrick Michaels expounds on the ruling's ominous implications:
The implications may be quite staggering. The decision means that carbon dioxide qualifies as a 'pollutant', something that causes net harm. This surely will open up a massive number of subsidiary cases. What levels of carbon dioxide emissions, if any, are allowed without being labeled pollutants? There is very little in our society that does not have some relationship to the production of carbon dioxide. Make no mistake -- we have now entered the era where the courts will enter into almost every aspect of our lives.The last I checked, the Constitution was designed specifically to prevent unaccountable, distant bureaucracies from imposing rules on Americans. Yet the EPA has essentially just been given a green-light to control every facet of American life. This can't be constitutional.
Then again, what do I know? I'm not a Supreme Court justice.