In the early 2000s, cities from São Paulo to Seoul were making measurable progress against the smog generated by cars and factory stacks. That progress is now being eroded from an unexpected direction. A report published by the World Meteorological Organization (WMO) to coincide with the UN's International Day of Clean Air found that surging wildfires and prolonged heatwaves — both intensified by climate change — are pushing air quality in the wrong direction across multiple continents, threatening to cancel out reductions that took governments decades to achieve. The mechanism is twofold.

Wildfire smoke carries dense concentrations of fine particulate matter and triggers oxidative stress deep inside the human body, which has been linked to asthma attacks, hospitalisations for chronic obstructive pulmonary disease (COPD), disrupted birth outcomes, and measurable effects on mental health. According to one study cited in the report, a tripling of wildfires since the 1990s contributed to nearly 100,000 deaths per year between 2010 and 2018. Meanwhile, the record heatwaves that scorched Europe and parts of Asia in recent summers are accelerating the formation of ground-level ozone — a pollutant that, once inhaled, effectively burns lung tissue and stresses the cardiovascular system. In heavily polluted regions, roughly one in five deaths from COPD is now attributed to long-term ozone exposure.

What makes the WMO's findings particularly alarming is the feedback loop they describe. The pollution produced by climate-driven wildfires and heat events itself contributes to further atmospheric warming, which in turn creates conditions more favourable to still more fires and heatwaves. "Air quality and climate cannot be treated as separate subjects; they are deeply intertwined and have to be treated together," said Lorenzo Labrador, a scientific officer at the WMO.