The Supreme Court is arguing whether the EPA must regulate carbon dioxide as a pollutant, due to its global warming effects.
http://www.cnn.com/2006/LAW/06/26/scotus.environment.ap/index.html This seems to me an interesting case. Unlike acid rain, or urban smog, or dioxin-tainted water, it's not intuitively obvious to me that gradual global warming is even a bad thing. Climate in Greenland, Canada, and Russia might benefit considerably. Even if global warming is indeed bad on balance, carbon dioxide is no synthetic industrial abomination, but a gas naturally occurring in vast quantities in the atmosphere already. Exhaled by every living animal. Necessary to every living plant. And emitted by most power plants and all internal combustion engines. It seems like laws regulating its output would fall somewhere between unenforceable, laughable, and fatal. "Sorry sir. You've exceeded your CO2 exhalation quota for the year. You can buy more carbon credits, or apply to start breathing again next January."
I think the problem is that the EPA has had notable success in preventing harm from chemicals used on a much smaller scale (DDT, lead, sulfur dioxide, mercury, CFCs). But CO2 is too freaking abundant, and too essential, to regulate using the same models.