Understanding and Addressing Temperature Impacts on Mortality

A large literature documents how ambient temperature affects human mortality. We compile longitudinal sub-national data from 115 countries and territories representing nearly 500M deaths, and use the data to revisit and synthesize key findings from this literature. We confirm that ambient temperature is among the largest external threats to human health, with heat and cold responsible for 3–15% of deaths across all countries in our sample, putting it among the top causes of death in many countries. In most contexts we consider, including low- and middle-income tropical countries, cold kills more than heat, though the temperature of minimum risk rises with age, making younger individuals generally more vulnerable to heat and older individuals more vulnerable to cold. We find evidence for adaptation to the local climate, with hotter places experiencing somewhat lower risk on hot days but often higher aggregate heat-related mortality due to more frequent exposure. Within countries, higher income is not associated with uniformly lower vulnerability to ambient temperature. Guided by these results, we systematically review the academic literature studying interventions that can moderate the impact of heat and cold on health, limiting our search to studies that resolve a plausibly causal relationship. Consolidating results across 52 studies, we find that many proposed and implemented interventions lack empirical support and do not target temperature exposures that generate the highest health burden. Further, some of the most beneficial interventions for reducing the health impacts of cold or heat have little explicit to do with the climate.