WMO Report: Wildfire and Heat-Wave Pollution Threatens Global Air Quality Efforts

A new report from the World Meteorological Organization (WMO) warns that rising pollution from wildfires and heat waves risks undermining international efforts to protect air quality and health. The annual Air Quality and Climate Bulletin, released for International Day of Clean Air for Blue Skies on Sept. 7, says pollutants such as fine particulate matter and ground-level ozone, and aerosols such as black carbon and microplastics, remain insufficiently monitored despite being widespread and harmful.

Fine particulate matter, or PM2.5 — particles smaller than 2.5 micrometers that can penetrate deep into the lungs and bloodstream — comes from industry, agriculture, heating, transport, wildfires and dust storms. In 2025, PM2.5 stayed above the long-term average in northern Canada, parts of Russia, west-central Africa and northwestern Spain because of heavy fire activity, while levels fell below average in China and stayed above average in India because of biomass burning, the bulletin found using four combined models for the first time.

Extreme wildfires are increasing: one study cited in the bulletin found extreme fire-smoke events have tripled globally since the 1990s, contributing to nearly 100,000 additional deaths a year between 2010 and 2018, a figure the WMO says may be an underestimate. A separate epidemiological study found that standard risk models based on total PM2.5 can underestimate wildfire-linked deaths by up to 93% because they miss the higher toxicity of fire particles.

Ground-level ozone, worsened by heat waves, is linked to increased mortality mainly through respiratory disease, with recent heat waves in the southeastern United States, Europe and China promoting its formation. Black carbon, or soot, reduces the sunlight reflected by snow and ice when deposited on them, hastening melting. One Earth System Model simulation estimated 51 million tonnes of microplastics on land and 22 million tonnes in the ocean, though the WMO says monitoring gaps make such estimates uncertain.