Wildfire smoke exposure and mortality burden in the USA under climate change

Wildfire activity has increased in the USA and is projected to accelerate under future climate change^1-3. However, our understanding of the impacts of climate change on wildfire activity, smoke and health outcomes remains highly uncertain because of the difficulty of modelling the causal chain from climate to wildfire to air pollution and health. Here we quantify the mortality burden in the USA due to wildfire smoke fine particulate matter (PM_2.5) under climate change. We construct an ensemble of statistical and machine learning models that link climate to wildfire smoke PM_2.5 and empirically estimate smoke PM_2.5-mortality relationships using data on all recorded deaths in the USA. We project that smoke PM_2.5 could result in 71,420 excess deaths (95% confidence interval: 34,930-98,430) per year by 2050 under a high-warming scenario (shared socioeconomic pathway scenario 3-7.0, SSP3-7.0)-a 73% increase relative to the estimated 2011-2020 average annual excess deaths from smoke. Cumulative excess deaths from smoke PM_2.5 could reach 1.9 million between 2026 and 2055. We find evidence for mortality impacts of smoke PM_2.5 that last up to 3 years after exposure. When monetized, climate-driven smoke deaths result in economic damages that exceed existing estimates of climate-driven damages from all other causes combined in the USA^4,5. Our research suggests that the health impacts of climate-driven wildfire smoke could be among the most important and costly consequences of a warming climate in the USA.