Global warming will cause significant harm to the health of persons and their communities by compromising food and water supplies; increasing risks of morbidity and mortality from infectious diseases and heat stress; changing social determinants of health resulting from extreme weather events, rising sea levels, and expanding flood plains; and worsening air quality, resulting in additional morbidity and mortality from respiratory and cardiovascular diseases. Vulnerable populations such as children, older persons, persons living at or below the poverty level, and minorities will be affected earliest and greatest, but everyone likely will be affected at some point. Family physicians can help reduce greenhouse gas emissions, stabilize the climate, and reduce the risks of climate change while also directly improving the health of their patients. Health interventions that have a beneficial effect on climate change include encouraging patients to reduce the amount of red meat in their diets and to replace some vehicular transportation with walking or bicycling. Patients are more likely to make such lifestyle changes if their physician asks them to and leads by example. Medical offices and hospitals can become more energy efficient by recycling, purchasing wind-generated electricity, and turning off appliances, computers, and lights when not in use. Moreover, physicians can play an important role in improving air quality and reducing greenhouse gas emissions by advocating for enforcement of existing air quality regulations and working with local and national policy makers to further improve air quality standards, thereby improving the health of their patients and slowing global climate change.