Global change presents humanity with unprecedented challenges. Climate change, altered natural cycles, and pollution of air, water, and biota threaten the very conditions on which human civilization has depended for the last 12 000 years. While human health is better now than ever before in human history, climate change is undermining many public health advances of the last century and ultimately may be associated with the unprecedented extinction of species. The increasing gap between the wealthy and poor—already unconscionable, and the cause of profound preventable morbidity and mortality—amplifies the effects of climate change on health and deepens health disparities.