The United States and Canada suffered the largest increase in fine particulate pollution (PM2.5) globally in 2023, fueled by the worst wildfire season in Canada’s history, according to the Air Quality Life Index (AQLI). The change is part of a trend—recent research suggests that climate change is causing an increase in the frequency of wildfires that is reversing decades of clean air progress made in the United States and potentially in other regions around the world.
The fires contributed to pollution levels not seen in over a decade in the United States and a 20 percent rise from 2022. The higher pollution concentrations were driven by the Canadian wildfires. The resulting pollution spread across Wisconsin, Illinois, Indiana, and Ohio, and even extended to Pennsylvania, Oklahoma, and as far south as Mississippi. Counties in these states were the 10 most polluted regions in the country—replacing counties in California which typically dominate the list.
Meanwhile, globally, air pollution remains the world’s greatest external risk to human health. Its impact on life expectancy is comparable to that of smoking, more than 4 times that of high alcohol use, 5 times that of transport injuries like car crashes, and more than 6 times that of HIV/AIDS.