Cleaner air could actually increase climate warming

A team from Kyushu University in Japan modelled the long-term effects of reductions in pollutants known as sulphate aerosols to see how they would impact the surface air temperature at current and increased carbon dioxide levels.

They found that temperatures would increase due to the loss of an overall cooling effect caused by the light-scattering particles.

“Air pollution causes an estimated seven million premature deaths per year worldwide, so action is essential, especially in emerging and developing countries, which tend to be most affected,” said Toshihiko Takemura, author of the study.

“However, reductions in air pollutants must come hand in hand with reductions in greenhouse gases to avoid accelerating global warming.”

Takemura used a complex climate simulation model that takes into account many key aspects of the atmosphere and oceans along with their interactions. It is widely used by news outlets for air pollution forecasts and is capable of predicting the mixing of aerosols in the atmosphere.

Looking at the immediate changes to the atmosphere in the case of reduced sulphate aerosols, which are typically produced from fuel sources, the researcher calculated that more energy overall enters the atmosphere. The increase was deemed to be similar regardless of whether the atmospheric carbon dioxide concentration is the same as present levels or doubled.

However, changes in the climate and surface temperatures over longer time scales showed that not only does the surface air temperature increase with a reduction in sulphate aerosols but this increase is even larger when carbon dioxide levels double.

“Although the fast response is similar for both situations, long-term changes caused by more slowly responding factors related to interactions with the oceans and subsequent changes, such as in clouds and precipitation, eventually leads to a bigger temperature increase,” Takemura explained.

“Thus, global warming will accelerate unless increases in greenhouse gas concentrations are suppressed as air pollution control measures decrease sulphate aerosol concentrations, further emphasising the urgency for reducing carbon dioxide in the atmosphere.”

Air pollution levels in many cities dropped last year due to the reduction in travel following the coronavirus lockdowns. However, one recent study found that these levels did not drop as much as scientists hoped.