The Clean Air Act mandates the EPA to regulate harmful pollutants such as particulate matter and ozone. Pollutants like carbon dioxide and other greenhouse gases, however, were long excluded under the law, since they don't harm human health directly but rather through the process of global warming. But two years ago those exceptions were eliminated when the Supreme Court ruled that the EPA could indeed regulate CO2 as a pollutant under the Clean Air Act. Problem was, the then Bush Administration EPA dragged its feet on any response to the ruling and even buried scientific evidence on the harmful effects of global warming. With Obama's election, that changed. On Sept. 30 new EPA Administrator Lisa Jackson announced that the Federal Government would begin the process of regulating CO2. It's still not clear what that will mean, and both Jackson and Obama have said they'd prefer Congress to take the lead on limiting CO2, but regulation remains a powerful weapon for environmentalists.