In 1998, the EPA privately contemplated its authority to regulate CO2 under the Clean Air Act. Congressman Tom Delay got wind of this and requested a formal opinion from the agency. EPA's general counsel, Jonathan Z. Cannon, wrote a memo arguing that CO2 was a pollutant under the Clean Air Act and thus subject to regulation by the agency.
LINK TO THIS ARTICLE
https://www.apeoplesepa.org/modules/cannon-memo-april-10-1998SOURCE
EPA's Authority to Regulate Pollutants Emitted by Electric Power Generation Sources
CITATION
Jonathan Z. Cannon, "EPA's Authority to Regulate Pollutants Emitted by Electric Power Generation Sources," EPA memo, April 10, 1998