Extreme wildfires and intensifying heatwaves are generating toxic airborne pollutants that risk reversing years of progress on air quality and public health, the World Meteorological Organization (WMO) warned on Monday. The United Nations' weather and climate agency, releasing its latest annual Air Quality and Climate Bulletin, said the twin challenges of air pollution and climate change are so deeply intertwined that neither can be addressed without the other. "Air quality and climate change can't be dealt with separately," said Lorenzo Labrador of the WMO's Global Atmosphere Watch network. "If one worsens, the other does too."

At the heart of the warning is PM2.5 — particulate matter composed of microscopic particles and droplets smaller than 2.5 micrometres in diameter, fine enough to penetrate deep into the lungs and enter the bloodstream. While regulations in Europe and North America have successfully curbed PM2.5 emissions from industry and transport, exposure to fire-generated PM2.5 has increased. Crucially, smoke particles from burning vegetation are significantly more toxic than those from other sources, including vehicle exhaust, yet conventional health risk models may be underestimating wildfire-attributable mortality by as much as 93 percent. One study cited in the bulletin found that extreme fire-smoke events have tripled globally since the 1990s, contributing to nearly 100,000 additional deaths per year between 2010 and 2018 — a figure the WMO cautioned may itself be an underestimate.

Beyond wildfire smoke, the report flags ground-level ozone as a mounting danger. Unlike the protective ozone layer high in the atmosphere, ground-level ozone forms when heat, stagnant air and intense solar radiation interact — conditions that have become more frequent during recent heatwaves in China, Europe and the southeastern United States. The WMO warned this rising ozone exposure could cause tens of thousands of additional premature deaths, primarily from respiratory disease.

The bulletin also raises alarm about aerosol particles and microplastics. Black carbon, or soot, deposited on snow and ice reduces the reflectivity of these surfaces, accelerating their melt. Microplastics — formed as plastics break down under sunlight — are now found in the air, soil and oceans alike; one simulation estimates 51 million tonnes on land and 22 million tonnes in the ocean, with both acting as further sources of atmospheric microplastics. The WMO said these pollutants travel vast distances and affect ecosystems far from their origin, yet remain insufficiently monitored.

The overarching message from the WMO is one of urgency and coordination. Piecemeal approaches — tackling industrial emissions while ignoring wildfires, or addressing climate change without factoring in air quality — will not be enough. The agency is calling for complementary, coordinated policies that treat these crises as the single, interlocking challenge they have become.