Some air pollution can block solar radiation – but cutting pollution is still the way to tackle global warming

Air pollution has numerous negative effects, from harming health to contributing to rising temperatures. However, research also shows a counter-intuitive result of air pollution – it can stop us from feeling some of the effects of climate change.

This is because pollutant particles such as sulphates and nitrates can create a kind of barrier to solar radiation. This process of “aerosol masking” cools the climate more than originally anticipated, according to a 2022 study by Oxford University.

But that doesn’t mean air pollution is a good thing. It does not prevent climate change – it just stops us feeling some of the impacts as intensely as we otherwise might.

Tackling pollutant particles is therefore definitely not at odds with efforts to halt climate change, for two main reasons. Firstly, this cooling effect applies only to some aerosols. Secondly, both air pollution and our climate require the same remedial action: eliminating fossil fuels.

So, what air pollutants are there, and how do they affect the global climate? And what can we do to improve both air quality and slow global warming at the same time?

Air pollution from fine particulates and ozone causes the premature death of 8.3 million people every year, according to a study published in the British Medical Journal (BMJ). Breathing in polluting particles or aerosols can lead to heart and lung diseases or even cancer.

Approximately 9 out of 10 aerosols occur naturally, according to NASA’s Earth Observatory. These include sulphates, organic carbon, mineral dust and sea salt. But the ones we need to be most concerned about are human-made aerosols, of which there are increasing amounts.

One of the primary sources of these human-made aerosols is burning fossil fuels – whether by cars, power plants or industrial processes. Doing so produces sulphur dioxide (SO2) that can go on to react with water and other gases to create sulphate aerosols. Fossil fuels are linked to more than 5 million excess deaths a year from air pollution, the BMJ study finds.

Another source or air pollution is biomass. Organic carbon and black carbon (soot) are sent into the air when forests or savanna are burned for farming or when agricultural waste, wood, dung or peat are used for fuel or cooking.

Whether natural or human-made, aerosols condense into water droplets. As the presence of some human aerosols increases, the amount of droplets also increases, and this reflects more sunlight and heat away from Earth and back into space, Oxford University’s atmospheric scientists explain.

China, which faces major air pollution issues, put in place one of the most stringent clean air policies the country had ever seen in 2013. Between the launch of these policies and 2017, researchers reported a significant drop in air pollutants such as SO2 and nitrogen oxides (NOx).

Yet average temperatures in China have increased by 0.7°C since 2014, according to Reuters, resulting in more intense heat waves. Taking the protective aerosol shield away may have contributed to this, scientists interviewed by Reuters suggest.

Many air pollutants affect our environment. Not all of them contribute to the “masking” of global warming, according to Reuters.

SO2 is the main one repelling the effects of the sun, and without it, global warming would already have exceeded the 1.5°C limit targeted by the Paris Agreement. In addition to harming the respiratory system, SO2 and other sulphur oxides can contribute to acid rain, which harms the foliage of trees and plants. The main cause of these emissions is coal combustion, meaning it is vital to drive down the use of coal.

Nitrogen oxides (NOx) are another air pollutant. They are a group of colourless gases emitted by industrial processes, vehicles and power plants. As NOx react with other chemicals in the atmosphere, they form small particles (particulate matter, particle pollution) that can contribute to the development of respiratory diseases such as asthma and play a part in acid rain.

NOx also influences the formation of surface ozone, which is activated by sunlight. The higher the temperatures, the more activation energy there is for NOx to react with other chemicals to form ozone. Unlike ozone in the stratosphere, which protects us from sunlight, surface ozone is a risk to humans and crops. Wheat and rice are particularly vulnerable to its effects, leading to lower yields and seed quality.

Sooty black carbon is emitted by engines that burn gas and diesel. It also results from the burning of biomass and has an impact on human health and the climate. As well as contributing to respiratory and cardiovascular issues, black carbon may also cause cancer and congenital disabilities.

Its ability to absorb light warms the air, affecting the climate. When it settles on the poles, it darkens the snow and ice. As a result, the ice caps lose their ability to reflect heat and light, accelerating their melting.

While some aerosols and other small particle pollution may mask global warming, this certainly does not make them desirable.

Some scientists have suggested enriching the atmosphere artificially with SO2 to act as a coolant to combat climate change. This process is called solar radiation management (SRM).

But critics say this could disrupt global climate patterns and potentially increase acid rain. In turn, this could impact the food and water cycle. SRM may also detract from attempts to accelerate the path to net zero greenhouse gas emissions.

As Oxford University’s atmospheric scientists underline, the impact of air pollution and global warming must be addressed jointly – and speedily – by focusing on driving down fossil fuels.

The World Economic Forum has many initiatives focused on decarbonization and clean air, including the Alliance for Clean Air, Industrial Clusters: The Net-Zero Challenge and Automotive and New Mobility.