Temperature extremes impact mortality and morbidity differently.

Increased temperature-related mortality is expected to significantly contribute to future economic damages from climate change, with declines in cold-related deaths outweighed by increases in heat-related deaths. While temperature-mortality relationships are well-documented, the effects of climate change on morbidity are less understood. Using data on emergency department (ED) visits, hospital admissions, mortality, and daily temperatures across California from 2006 to 2017, we find distinct differences in the temperature-response functions of these health outcomes, influenced by age distribution and underlying causes of morbidity and mortality. These differential responses fundamentally shape the burden of future climate change: We project that while future warming will increase ED visits, mortality will decrease due to fewer cold extremes. These results underscore the need to quantify temperature-morbidity responses to fully understand and anticipate the health impacts of climate change and suggest that local declines in mortality due to warming can mask economically meaningful increases in temperature-driven morbidity and health care utilization.