EPA, "Greenhouse Gas Endangerment Finding" (December 15, 2009)

In 2007, the Supreme Court had ruled that greenhouse gases were pollutants under the Clean Air Act. According to that act, if a pollutant was found to endanger public health and welfare, the EPA was obligated to regulate it. Under President Obama, the EPA concluded that greenhouse gases were such a danger, prompting the EPA to promulgate greenhouse gas regulations in the following years.