With rising temperatures, more frequent extreme weather events, and a host of effects on air quality, food supply, and infectious diseases, climate change is projected to have a major impact on human health and well-being. In many places, these effects are already being felt. In this part 3 of a 3-part series, Dr. Kim Knowlton, senior scientist with the Natural Resources Defense Council’s health and environment program, provides a detailed discussion on the human health chapter of the Third National Climate Assessment.