A good formula for leveraging health messaging for climate advocacy: Tell people about the health consequences of climate change, health benefits of climate solutions, and include a call-to-action. This experiment found that each of these categories was worth including in a message to help motivate Americans to contact Congress. Within each of these categories, a variety of specific types of information were tested, with the most effective overall combination being a message that first described the negative impacts of climate change on air quality, then explained how transitioning to clean energy will benefit people’s health, and ended by explaining that most Americans support this solution, and many are taking action to advocate for it.