Historical increases in heat wave exposure due to population and climate changes

Abstract Understanding how exposure to extreme heat evolves over time is crucial for minimizing heat-related mortality. Here, we divide past changes in heat exposure into components from 1. births and deaths, 2. immigration, 3. local population movement, 4. spatially averaged climate changes, and 5. local climate changes. Globally, heat wave exposure has more than doubled over the past three decades, with worldwide population growth contributing almost half of this increase. Population movement and global climate changes, meanwhile, have each contributed significant increases in exposure (20% and 30%, respectively), while regional climate changes have decreased exposure because the largest increases in heat waves have occurred in less populated areas. The relevant factors differ across countries and continents, with total population growth being dominant in India and much of Africa, climate changes being dominant in China and most of Europe, and both being important in the United States and elsewhere. These results indicate that each country must understand the drivers of their exposure to climate to effectively minimize damages.