The July 2026 North American wildfire smoke event was three times deadlier due to climate change

Dmitri A. Kalashnikov , Emily L. Williams, John Abatzoglou, Cong Yin, Wenli Ni, Nicholas Nassikas

In mid-July 2026, numerous fast-burning wildfires affected western Ontario and northern Minnesota, resulting in extensive smoke plumes across eastern North America. Here, we conduct a rapid attribution analysis of the 14–21 July smoke event, quantifying the change in wildfire smoke (WFS) PM2.5 concentrations and mortality compared to a counterfactual world without anthropogenic climate change (ACC). We find that ACC increased WFS PM2.5 concentrations by approximately three-fold. As a result, population exposure to regulatory exceedances of WFS PM2.5 concentrations (>35 µg/m3) amounted to 268 million person-days, of which 157 million are attributable to ACC. We estimate 770 excess deaths attributable to observed WFS PM2.5 exposure, a three-fold increase compared to a counterfactual world without ACC. This rapid impact-attribution assessment of WFS PM2.5-related mortality provides a methodological framework for quantifying the ACC contribution to other acute air pollution episodes globally.