A new WMO report sheds light on the complex link between air quality and climate, highlighting the significant role that aerosols have in wildfires, winter fog, shipping emissions and urban pollution.
The report highlights the need for improved atmospheric monitoring and more integrated policies to safeguard human and environmental health and reduce agricultural and economic losses.
The WMO Air Quality and Climate Bulletin No. 5 – September 2025, which examines trends and geographical distribution of air pollution in 2024 as well as progress and challenges in forecasts and warnings, was released on September 7 to coincide with the International Day of Clean Air for Blue Skies.
Ko Barrett, WMO deputy secretary general, said, “Climate change and air quality cannot be addressed in isolation. They go hand in hand and must be tackled together in order to protect the health of our planet, our communities and our economies.”
According to the World Health Organization (WHO), ambient air pollution is estimated to cause more than 4.5 million premature deaths worldwide each year, with huge environmental and economic costs.
“Climate impacts and air pollution respect no national borders – as exemplified by intense heat and drought, which fuel wildfires, worsening air quality for millions of people. We need improved international monitoring and collaboration to meet this global challenge,” continued Barrett.
The key findings of the report were as follows:
Particulate matter
Particulate matter from activities such as transportation, industry and agriculture, as well as from wildfires and wind-blown desert dust, remain a major health hazard.
The report found that PM2.5 levels (particulate matter 2.5 microns in diameter or smaller) were at above-average levels in Canada, Siberia and Central Africa due to wildfire activity.
The highest anomaly was found in the Amazon basin. Record wildfires in the Amazon region and drought-fueled fires in northern South America have resulted in a measurable degradation in air quality in far-away, densely populated urban centers in Brazil, according to the WMO.
Wildfires are a significant contributor to particle pollution, and the problem is expected to increase as the climate warms, posing growing risks for infrastructure, ecosystems and human health.
Aerosols
Aerosols can both warm and cool the atmosphere, depending on their composition. Darker ones, such as black and brown carbon, warm the atmosphere and melt the ice or glaciers they land on.
Brighter aerosols, such as sulfates, reflect solar radiation back to space and can therefore provide temporary cooling before depositing as acid rain and snow.
Concentrations of aerosols in the atmosphere increased globally from the 1950s to the 1980s but have come down substantially since then due to concerted efforts in North America, Europe and, later, East Asia, according to the WMO.
They continue to rise in some regions such as South Asia, South America and the northern latitudes due, in part, to increasing wildfires.
The link between aerosols, reactive gases and long-lived greenhouse gases is complex, and a proper understanding of these interactions is required to develop mitigation measures for both climate and air quality. Therefore, the WMO argues that it is important to take an integrated approach to managing emissions, to protect not only the climate but also the ecosystem and human health.
Winter fog
The Indo-Gangetic Plain, home to over 900 million residents, is among the most densely populated and agriculturally active regions in the world and has experienced a marked rise in air pollution and winter fog.
Although fog is a seasonal occurrence, its growing frequency and duration are increasingly linked to pollution from vehicles, construction, heating, cattle and burning of vegetation.
“Persistence of fog is no longer a simple, seasonal weather event – it is a symptom of escalating human impact on the environment,” the bulletin states. “Addressing this requires comprehensive strategies, such as enforcing regulations on agricultural residue burning, and promoting cleaner energy for cooking, heating, lighting and public transport systems.”
Atmospheric composition monitoring infrastructure
The report highlights the importance of atmospheric monitoring infrastructure, such as ozone studies, pollen forecasting and atmospheric deposition.
It states that ground-based monitoring networks are essential for calibration and validation, particularly in developing countries where infrastructure remains sparse.
In related news, the latest World Meteorological Organization (WMO) El Niño/La Niña update predicts that the La Niña climate pattern may return to affect weather from September onward, although temperatures are still expected to be above average for much of the world
