On October 20, 1999, a group of private organizations filed a rulemaking petition asking EPA to regulate “greenhouse gas emissions from new motor vehicles under §202 of the Clean Air Act.” D requested public comment on “all the issues raised in [the] petition,” adding a “particular” request for comments on “any scientific, technical, legal, economic or other aspect of these issues that may be relevant to EPA’s consideration of this petition.” On September 8, 2003, D entered an order denying the rulemaking petition. It stated that the Clean Air Act does not authorize D to issue mandatory regulations to address global climate change, and (2) that even if the agency had the authority to set greenhouse gas emission standards, it would be unwise to do so at this time. D believed that greenhouse gases could not be “air pollutants” within the meaning of the Act. D determined in 2003 that it lacked authority under the Clean Air Act to regulate carbon dioxide and other greenhouse gases and even if it did it had no authority to regulate carbon dioxide and other GHGs in relation to global warming. Ps assert that D does have authority over global warming and greenhouse gases because of the broad wording of the statute and that D's decision not to regulate greenhouse gases exceeded the scope of its discretion under the law. They claim D violated the Act by not giving it effect. Section 202(a)(1) of the Clean Air Act, 42 U.S.C. § 7521(a)(1), requires the administrator of D to set emission standards for 'any air pollutant' from motor vehicles or motor vehicle engines 'which in his judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare.' The U.S. Court of Appeals for the District of Columbia Circuit decided on September 13, 2005, to uphold the decision of D. The lower court was sharply divided on whether Ps had 'standing' - a personalized injury creating a right to use the courts (as opposed to the Congress) to obtain government action. One of the three judges found no standing while a second of three postponed a factual decision for any later trial. Ps have asked the court to answer two questions concerning the meaning of §202(a)(1) of the Act: whether EPA has the statutory authority to regulate greenhouse gas emissions from new motor vehicles; and if so, whether its stated reasons for refusing to do so are consistent with the statute.