CINDY L. PARKER, MD, MPH, is Co-Director of the Program on Global Sustainability and Health at the Johns Hopkins University Bloomberg School of Public Health. She is also a Fellow of the American College of Preventive Medicine. She began her career as a family practice physician and, then recognized that she could help people more by by focusing on preventing health problems before they started. Climate change is, in her view, the most health-damaging problem humanity has ever faced.