On December 7, 2009, the Administrator of the Environmental Protection Agency (EPA) issued findings declaring first, that a combination of six greenhouse gases (carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride) constitute the root cause of human-induced climate change and threaten both the public health and the public welfare (Endangerment Finding); and second, that greenhouse gas emissions from motor vehicles contribute to that threat.