EPA officially issued its proposed finding that six "greenhouse gases (GHG) in the atmosphere endanger the public health and welfare of current and future generations." According to EPA, "high atmospheric levels [of GHGs] are the unambiguous result of human emissions, and are very likely the cause of the observed increase in average temperatures and other climatic changes." EPA also "proposes to find that the emissions of these substances from new motor vehicles and new motor vehicle engines are contributing to air pollution which is endangering public health and welfare under section 202(a) of the Clean Air Act." According to EPA Administrator Lisa Jackson, these proposed findings mark "the first formal recognition by the U.S. government of the threats posed by climate change." They pave the way for EPA to regulate GHGs under the Clean Air Act unless Congress preempts further EPA regulation by passing its own Climate Change law. The six greenhouse gases identified by EPA are: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.