On August 3, 2015 the United States Environmental Protection Agency (EPA) issued guidelines to reduce the emissions of carbon dioxide (CO2) from power plants. This action, known as the Clean Power Plan, is the single biggest step the United States has taken to address climate change. CO2 accounts for more than 80% of greenhouse gas emissions in the US. The Clean Power Plan will result in a 32% reduction of CO2 emissions from the 2005 level by 2030. This reduction will mitigate climate change and substantially improve air quality and public health. In 2009, the health impacts of climate change were described by the University College of London-Lancet Commission as the biggest public health threat of the century. More recently the 2015 Lancet Commission reported climate change was also the greatest public health opportunity of the century. We urge physicians to seize this opportunity to prevent human illness in the US and around the world.