Climate change could have a devastating effect on human and environmental health. Potential effects of climate change on human health include higher rates of respiratory and heat-related illness, increased prevalence of vector-borne and waterborne diseases, food and water insecurity, and malnutrition. Persons who are elderly, sick, or poor are especially vulnerable to these potential consequences. Addressing climate change could have substantial benefits to human health. In this position paper, the American College of Physicians (ACP) recommends that physicians and the broader health care community throughout the world engage in environmentally sustainable practices that reduce carbon emissions; support efforts to mitigate and adapt to the effects of climate change; and educate the public, their colleagues, their community, and lawmakers about the health risks posed by climate change. Tackling climate change is an opportunity to dramatically improve human health and avert dire environmental outcomes, and ACP believes that physicians can play a role in achieving this goal.