Valuing wildfire smoke-related mortality benefits from climate mitigation

Human-induced climate change has increased wildfire risks, associated air pollution, and health damages in North America. Despite its large potential for damage, climate-induced wildfire smoke is rarely incorporated in estimates of the societal costs of climate change. We develop an integrated framework to estimate air pollution from climate-induced wildfire smoke (fine particulate matter, PM_2.5) and the associated mortality damage in the United States across different trajectories of greenhouse gas emissions and global mean surface temperature. Our framework accounts for fire-vegetation feedbacks by empirically estimating the effects of past fires on future burn probability. Under 3 °C of global warming (relative to 1850-1900), we estimate that smoke exposure will lead to 64,000 deaths annually in the United States (95% CI: 33,500 to 112,300; calculated using historical population), a 60% increase above estimated annual smoke deaths during 2011-2020. Limiting global warming to 2 °C reduces smoke-related mortality by 14% (8,900 deaths per year) relative to our estimate for 3 °C. For every additional tonne of CO₂ emissions in 2025, we calculate a net present value of monetized damage (i.e., a partial social cost of carbon) of $11.2 (95%CI: [Formula: see text]$1.1 to $41.6; 2020USD) due to climate-induced wildfire smoke mortality in the United States. Incorporating wildfire smoke damages into existing nonwildfire damage estimates increases the US domestic social cost of carbon by 74%, substantially increasing the expected benefits of greenhouse gas mitigation within the United States.