There is scientific consensus that the climate is changing, that human activity plays a major role, and that the changes will continue through this century. Expert consensus holds that significant health effects are very likely. Public health and health care systems must understand these impacts to properly pursue preparedness and prevention activities. All of medicine will very likely be affected, and certain medical specialties are likely to be more significantly burdened based on their clinical activity, ease of public access, public health roles, and energy use profiles. These specialties have been called on to consider the likely impacts on their patients and practice and to prepare their practitioners. Emergency medicine (EM), with its focus on urgent and emergent ambulatory care, role as a safety-net provider, urban concentration, and broad-based clinical mission, will very likely experience a significant rise in demand for its services over and above current annual increases. Clinically, EM will see amplification of weather-related disease patterns and shifts in disease distribution. In EM's prehospital care and disaster response activities, both emergency medical services (EMS) activity and disaster medical assistance team (DMAT) deployment activities will likely increase. EM's public health roles, including disaster preparedness, emergency department (ED)-based surveillance, and safety-net care, are likely to face increasing demands, along with pressures to improve fuel efficiency and reduce greenhouse gas emissions. Finally, EM's roles in ED and hospital management, particularly related to building and purchasing, are likely to be impacted by efforts to reduce greenhouse gas emissions and enhance energy efficiency. Climate change thus presents multiple clinical and public health challenges to EM, but also creates numerous opportunities for research, education, and leadership on an emerging health issue of global scope.