The Environmental Protection Agency is being urged by multiple states to take action as quickly as possible regarding regulating greenhouse gas emissions from automobiles. Eighteen states are responsible for sending the letter to Administrator Jackson that asks her to, “act as soon as possible by issuing a determination pursuant to 42 U.S.C. 7521(a)(1) that greenhouse gas emissions are endangering public health and welfare.” Such a determination is called an "endangerment finding," and, as the Supreme Court held in Massachusetts v. EPA, the EPA has the authority to make an endangerment finding with respect to greenhouse gas emissions. And, if the EPA makes such a finding, it will have authority under the Clean Air Act to regulate greenhouse gas emissions.