This course is an introduction to the multiple ways our changing climate affects global population health, and to promising policy and practice responses. More intense storms, heatwaves, and rising seas mean many, particularly the most vulnerable, now face growing risks of weather-related injury, illness, mental stress and even death. Because people care deeply about health outcomes, public health has great potential to convey the urgency of reducing greenhouse gas emissions and adapting to a warmer, more unpredictable climate. The main message of the course is that public health must therefore “lean in” and become a more central player in climate change mitigation and adaptation. Because climate-related health risks happen mainly at the local level, the course focuses on cities – increasingly key players in climate change policy. Starting with an overview of the science consensus suggesting we have 10-20 years to prevent risks associated with exceeding 1.5°C of global warming and put in place adaptive policies, the course provides interactive lectures, expert interviews and case studies that build practical knowledge. In the final assignment, participants apply course tools and strategies to a city of their choice, preparing them to contribute to climate mitigation and building health resiliency in their own local context.