I understand that you pasted that quote from a news-service, but it is quite an overstatement. The court did not hold that carbon dioxide is a pollutant under the Clean Air Act. Instead, the Court held that EPA has the authority to regulate carbon dioxide as a pollutant under the Act, and that EPA's decision not to regulate carbon dioxide was arbitrary and capricious because its given reasons were not rooted in the statute itself. EPA must now either promulgate regulations establishing emission limitations for carbon dioxide or give a reasonsed explanation (based on the statute) why it won't establish such regulations.
to Justice Stevens