THE U.S. CLEAN Air Act (CAA) was passed by the U.S. Congress in 1963 and strengthened with amendments passed in 1970, 1977, and 1990. The U.S. Environmental Protection Agency (EPA) is responsible for implementation and regulation of the CAA, although much of the work falls to state and local governments. EPA regulates many pollutants (such as particulate matter) that play an important role in the Earth's radiation balance, but CAA has not been used to regulate greenhouse gases (GHGs), the pollutants most responsible for global warming. A 2007 U.S. Supreme Court decision ruled that GHGs fall within the jurisdiction of the EPA and the CAA, forcing the EPA to re-examine its ruling on this matter.

The first U.S. federal legislation dealing with air pollution was the ...