Are you referring to the Massachusetts vs EPA case? I thought that 5-4 decision had to do with automobile emissions, not specifically CO2.
Yes, that's the case. I am not a lawyer, but the ruling specifically mentions CO2:
Based on respected scientific opinion that a well-documented rise inglobal temperatures and attendant climatological and environmental changes have resulted from a significant increase in the atmospheric concentration of “greenhouse gases,” a group of private organizations petitioned the Environmental Protection Agency (EPA) to begin regu-lating the emissions of four such gases, including carbon dioxide, un-der §202(a)(1) of the Clean Air Act, which requires that the EPA“shall by regulation prescribe . . . standards applicable to the emis-sion of any air pollutant from any class . . . of new motor vehicles . . . which in [the EPA Administrator’s] judgment cause[s], or contrib-ute[s] to, air pollution . . . reasonably . . . anticipated to endangerpublic health or welfare,” 42 U. S. C. §7521(a)(1).
So it seems to be about both auto emissions and CO2.
Unfortuantely, the GWB EPA conceded that the govt. should do something about "global climate change."
"The Court attaches considerable significance to EPA’s espoused belief that global climate change must be addressed.."