In 2019, the U.S. Call to Action on Climate, Health, and Equity named climate change the "greatest public health challenge of the 21st century." The past ten to fifteen years have seen tremendous growth in the climate-health nexus with the creation of wide-reaching global consortiums, centers, and research journals, and development of degree and training programs. Using historical and ethnographic approaches to map the emergence and gradual institutionalization of the "climate medicine" field, I attend to how and why U.S. physicians have recognized and mobilized in response to climate change and its health impacts amidst the many potential and ongoing complexities of doing so. I argue that physicians and the medical community have sought to address climate change through largely non-reductive approaches—from educating patients and policymakers and seeking to address the upstream causes that impact patient health, while leveraging scientific expertise and authority. This project offers insight into medical activism, the climate-health movement, curricular reform, and processes like medicalization, and professionalization to understand how medical and academic communities may inspire novel responses to the climate crisis.