Wildfires and Heat Waves Threaten Air Quality Gains, WMO Warns

The World Meteorological Organization (WMO) released its annual report on climate and air quality on Monday, World Clean Air Day, warning that extreme heat and intensifying wildfires are undoing years of pollution reduction. Stricter regulations have cut industrial and traffic emissions in Europe and North America, but the gains are increasingly threatened by wildfire smoke and heat-driven ozone — two hazards that are becoming more frequent as the climate warms.

Wildfire Smoke: Deadlier Than Known

Particulate matter from burning vegetation — so-called PM2.5 particles, smaller than 2.5 micrometers — can penetrate deep into the lungs and enter the bloodstream, raising the risk of heart attacks, arrhythmias, strokes and pulmonary embolism. According to the WMO, smoke from wildfires is significantly more toxic than equivalent concentrations of exhaust-based particles.

Extreme wildfire smoke events have tripled globally since the 1990s, the report found. Between 2010 and 2018, they may have contributed to nearly 100,000 additional deaths per year — and even that figure may be an underestimate. Conventional risk models that only account for total PM2.5 concentration can underestimate wildfire-smoke mortality by up to 93 percent, the WMO warned, because they fail to capture the particular toxicity of combustion particles from wood and vegetation.

Heat Waves Drive Ground-Level Ozone

A second major risk is ground-level ozone. Unlike the beneficial ozone layer high in the atmosphere, ozone near the surface is a harmful irritant gas. High temperatures and intense sunlight accelerate its formation — the precise conditions that occur during heat waves. Elevated ground-level ozone has been recorded recently across Europe, China and the southeastern United States. Long-term ozone exposure is linked to higher mortality from respiratory diseases, and the WMO estimates that rising ozone levels could cause tens of thousands of additional premature deaths.

Soot and Microplastics Poorly Monitored

The WMO is calling for better, more coordinated global monitoring of air pollutants. Besides fine particles and ozone, the report highlights aerosols such as soot and the growing presence of microplastics in the atmosphere. Despite being widespread and potentially damaging to ecosystems, these substances are currently under-monitored. The report was released using data from the WMO's Global Atmosphere Watch network.