Thermal stress, food poisoning, infectious diseases, malnutrition, psychiatric illness as well as injury and death from floods, storms and fire are all likely to become more common as the earth warms and the climate becomes more variable. In contrast, obesity, type II diabetes and coronary artery disease do not result from climate change, but they do share causes with climate change. Burning fossil fuels, for example, is the major source of greenhouse gases, but it also makes pervasive physical inactivity possible. Similarly, modern agriculture's enormous production of livestock contributes substantially to greenhouse gas emissions, and it is the source of many of our most energy-rich foods. Physicians and societies of medical professionals have a particular responsibility, therefore, to contribute to the public discourse about climate change and what to do about it.