A new report from the World Meteorological Organization (WMO) warns that rising wildfire activity and increasingly frequent heatwaves are making it harder to improve air quality and protect human and ecosystem health.
The WMO’s latest Air Quality and Climate Bulletin, released for the International Day of Clean Air for blue skies on 7 September, highlights growing exposure to wildfire smoke, alongside the worsening risk of ground-level ozone during extreme heat.
The result is a growing wildfire air pollution challenge that existing air-quality policies may not fully address.
The report calls for better atmospheric monitoring and closer coordination between climate and air-quality policies, particularly as wildfire smoke can be more toxic than conventional pollution models suggest.
Wildfire smoke is becoming a bigger health threat
Fine particulate matter known as PM2.5 is among the most significant pollutants associated with wildfire smoke. These particles are smaller than 2.5 micrometres across, allowing them to penetrate deep into the lungs and enter the bloodstream.
Although PM2.5 is also produced by transport, industry, agriculture and residential heating, the contribution from fires is becoming increasingly important.
The WMO says exposure to fire-related PM2.5 has risen even as regulations have helped reduce emissions from industry and transport across Europe and North America.
The bulletin reports that PM2.5 concentrations were above their long-term average in northern Canada, parts of Russia, and western-central Africa in 2025 because of increased fire activity. Northwestern Spain also experienced unusually high levels following exceptional late-summer fires.
A different pattern was seen in Amazonia, where burning was lower than in previous years. China continued to record below-average PM2.5 concentrations, reflecting falling emissions from human activities, while India remained above average, partly because of biomass burning.
Extreme fires could be causing more deaths than models show
The scale of wildfire air pollution is particularly concerning because smoke does not simply behave like conventional sources of PM2.5.
Research highlighted by the WMO indicates that extreme fire-smoke events have tripled globally since the 1990s. One study estimated that wildfire smoke contributed to almost 100,000 additional deaths each year between 2010 and 2018, although the true figure could be higher.
There is also evidence that standard air-quality risk assessments may underestimate the danger. One epidemiological study found that models based on overall PM2.5 exposure could underestimate wildfire-attributable mortality by as much as 93%.
That finding points to a significant weakness in current assessments: the toxicity of particles produced by fires can differ from that of PM2.5 generated by other sources.
Heatwaves are adding another layer of pollution
Wildfires are not the only climate-related threat to air quality. The WMO also highlights the growing problem of ground-level ozone, which can worsen during heatwaves.
High temperatures, stagnant air and intense sunlight create conditions that favour ozone formation. Recent research from southeastern USA, Europe, and China has linked heatwave conditions with increased ozone exposure.
Long-term exposure to ground-level ozone is associated with higher mortality, particularly from respiratory disease. The WMO warns that increasing ozone exposure during extreme heat could result in tens of thousands of additional premature deaths.
This creates a feedback between climate and air quality: the conditions associated with a warming climate can intensify pollution, while some air pollutants themselves influence the climate system.
Better monitoring is urgently needed
The WMO says stronger atmospheric observation systems are needed to understand these interconnected risks.
Its assessment draws on data from the Global Atmosphere Watch (GAW) Programme and, for the first time, incorporates models from four different sources. Despite differences in their inputs and methodologies, the results were broadly consistent.
The report also highlights pollutants that receive comparatively little sustained monitoring, including black carbon and microplastics.
These aerosols can travel thousands of kilometres, crossing borders and oceans. Black carbon deposited on snow and ice can reduce their reflectivity and accelerate melting, while microplastics are now detected throughout the atmosphere, on land and in the oceans.
For policymakers, the message is clear: wildfire air pollution and climate change cannot be tackled separately. The WMO argues that coordinated action on emissions, climate and atmospheric monitoring will be essential if recent progress on air quality is not to be reversed.
