On April 2, 2007, in Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court found that greenhouse gases are air pollutants covered by the Clean Air Act. The Court held that the Administrator must determine whether or not emissions of greenhouse gases from new motor vehicles cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare, or whether the science is too uncertain to make a reasoned decision. In making these decisions, the Administrator is required to follow the language of section 202(a) of the Clean Air Act.
The Obama EPA has completed its study of the public health impact of greenhouse gases and is now asking for public comments on its findings. The proposed findings by EPA do not contain any new regulations. However, it is reasonable to expect that new regulations or new laws will come in the future to regulate these greenhouse gases.
In case anyone thinks that EPA has gone wild, this is a reminder that it was the conservative-leaning Supreme Court that ruled two years ago that EPA does have the authority to regulate greenhouse gases under the Clean Air Act if they are determined to be harmful to public health and welfare.