China saw a decline in overall air pollution levels of health-harmful particulate matter (PM) 2.5 in 2024 as compared to 2023 thanks to ardent mitigation efforts of leading pollution sources.

But India remained a global air pollution hotspot, while wildfire activity led to above average PM 2.5 levels in Canada, Siberia and central Africa, according to the latest Air Quality and Climate Bulletin of the World Meteorological Organization (WMO), released on Friday.

Highest rise in the Amazon  

The biggest anomaly, however, was in the Amazon basin where dramatic increases in air pollution, as compared to 2023 levels, were driven by record wildfires and drought-fuelled fires in northern South America. Both wildfires and droughts are being worsened by climate change.

Wildfires are a big contributor to particle pollution and the problem is expected to increase as the climate warms, posing growing risks for infrastructure, ecosystems and human health, warns the new WMO bulletin. It also underlines the “vicious cycle” that global warming is exacerbating.

As its title suggests, the report traces the complex interplay between air quality and climate, highlighting the role of tiny particles called aerosols in wildfires, winter fog, shipping emissions and urban pollution in climate trends – mainly warming, but some cooling as well. It stresses the need for improved atmospheric monitoring and more integrated policies to safeguard human and environmental health and reduce agricultural and economic losses.

“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,” WMO Deputy Secretary-General Ko Barrett said.

A ‘complicated’ picture

WMO experts described the bulletin as presenting a “complicated” picture as there were both reasons for cheer and gloom.

The bulletin highlighted that PM2.5 released from transport, industry, agriculture, wildfires and wind-blown desert dust is a major health hazard. PM2.5 are air pollutants that are is 1/28 of the width of a human air or smaller and can do great damage to human health as they can enter the bloodstreams through the lungs, and even enter the brain.

Human activities that involves the burning fossil fuels are releasing black carbon, nitrous oxide and ground-level ozone, which in turn aggravate climate change due to their greenhouse effect of causing the planet to warm faster. The bulletin terms this as a “vicious cycle” when combined with climate change pressures.

“Climate impacts and air pollution respect no national borders – as exemplified by intense heat and drought which fuels wildfires, worsening air quality for millions of people. We need improved international monitoring and collaboration to meet this global challenge,” Barrett said.

In the Indo-Gangetic plain where nearly 900 people live, air pollution is worsening winter fog both in intensity and in length.

“Persistence of fog is no longer a simple, seasonal weather event – it is a symptom of escalating human impact on the environment. 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,” the bulletin said.

Spotlight on aerosols 

The bulletin placed special emphasis on aerosols that are tiny airborne particles. Aerosols can have both a warming or a cooling affect depending on their composition.

Darker ones, such as black carbon that is released when the combustion is incomplete, can warm the atmosphere and melt the ice or glaciers that they land on. But the brighter aerosols such as sulphates tend to have a temporary cooling effect as they reflect solar radiation back to space before returning to the earth’s surface in the form of acid rain and snow.

In 2020, UN agency International Maritime Organization (IMO) put regulations in place capping the use of sulphates in shipping fuel and bring it down. This has translated into a decrease in premature mortality and a decrease in childhood asthma cases, particularly in the South Asia and Africa, Lorenzo Labrador, WMO’s scientific officer said.

It also has had an unintended environmental consequence.

“So that [reduction in sulphur emissions] results, or translates into a very slight increase in the temperature of 0.04 degrees in 2025 so what we have here, and this is very important to emphasize, is not an increase in temperature due to aerosols, but rather an unmasking of the true warming of greenhouse gasses as a result of the offset that these aerosols were having,” said Lorenzo Labrador, WMO’s scientific officer.

Sulfide aerosols were previously making the clouds brighter and thus helped the clouds reflect more light into space, cooling off temperatures, Labrador explained.

Bulletin underscores the importance of monitoring

This is the first time that the WMO experts used estimates from three different models for this bulletin, and while there were minor differences, all models had the same conclusion.

The Bulletin also underscored the importance of ramping up the atmospheric monitoring infrastructure, especially in developing regions. While satellites do provide critical insights for the globe, ground-based monitoring networks are also essential to validate that data. In developing countries this infrastructure still remains sparse, WMO experts said.

WMO experts also drew attention towards the positive finding of the report. “When we see that countries or regions or cities are taking measures to fight against bad air quality, it works, and we see that in many areas, an improvement of the air quality,” said Paolo Laj who is the Chief of Global Atmosphere. “But globally, in regions where these measures have been taken, there is a great improvement of the air quality,” he said.

Image Credits: Mike Newbry/ Unsplash, WMO.