Climate change, health equity, social and environmental justice, sustainability: These are each hugely important and complex issues in their own right. But we cannot afford to address them separately: The root causes are the same, the stakes too high, the need for action too urgent, and the opportunities for synergy too great. People in the United States and around the world are already experiencing the effects of climate change. These effects will increase as the global and local impacts of climate change worsen. At the same time, increasing levels of social inequality heighten persistent and unacceptable health inequities. Climate change will even further exacerbate health inequities.