In 2009, when carbon dioxide (CO2) levels were at 387.43 parts per million, the Center for Biological Diversity and 350.org submitted a citizen petition calling on the U.S. Environmental Protection Agency to take steps necessary to institute a national ambient air quality standard (NAAQS) for greenhouse gas (GHG) emissions under §§108-110 of the Clean Air Act (CAA). For 12 years, the petition was simply ignored. Then, the day President Donald Trump left office, outgoing EPA Administrator Andrew Wheeler issued a letter denying the petition.