The health sector, whose mission is protecting and promoting health, makes a major contribution to the climate crisis — the greatest health threat of the 21st century — and therefore has an important role to play in resolving it. Health care’s climate footprint is equivalent to 4.4% of global net emissions (2 gigatons of carbon dioxide equivalent). The global health care climate footprint is equivalent to the annual greenhouse gas emissions from 514 coal-fired power plants. If the health sector were a country, it would be the fifth-largest emitter on the planet. Health investment and policy must be retooled to support decarbonization. If the health sector — individual health facilities, health systems, ministries of health, international and bilateral development agencies, and private health care organizations — all take action toward this goal, it can be achieved. If health care development, growth, and investment can align with global climate goals, the 10% of the world economy that health care represents, together with its political influence at every level of government, can help provide leadership for a low-carbon, climate-smart, more equitable, and healthier future.