Responding to our decision in Massachusetts, EPA undertook greenhouse gas regulation. In December 2009, the agency concluded that greenhouse gas emissions from motor vehicles "cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare," the Act's regulatory trigger. §7521(a)(1); 74 Fed. Reg. 66496. The agency observed that "atmospheric greenhouse gas concentrations are now at elevated and essentially unprecedented levels," almost entirely "due to anthropogenic emissions," id., at 66517; mean global temperatures, the agency continued, demonstrate an "unambiguous warming trend over the last 100 years," and particularly "over the past 30 years," ibid. Acknowledging that not all scientists agreed on the causes and consequences of the rise in global temperatures, id., at 66506, 66518, 66523-66524, EPA concluded that "compelling" evidence supported the "attribution of observed climate change to anthropogenic" emissions of greenhouse gases, id., at 66518. Consequent dangers of greenhouse gas emissions, EPA determined, included increases in heat-related deaths; coastal inundation and erosion caused by melting icecaps and rising sea levels; more frequent and intense hurricanes, floods, and other "extreme weather events" that cause death and destroy infrastructure; drought due to reductions in mountain snowpack and shifting precipitation patterns; destruction of ecosystems supporting animals and plants; and potentially "significant disruptions" of food production. Id., at 66524-6653