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Cleaner air complicates global warming

Air pollution

Our attempts to clean up the air is having an unexpected effect, scientists say. Fewer atmospheric aerosols means we may feel the full force of climate change (Image: iStockphoto)

Improving air quality may lead to much higher global temperatures than predicted, researchers say.

This is because having fewer aerosols in the atmosphere will unmask the full effect of climate change, the scientists argue in today's issue of the journal Nature.

The researchers say temperatures may rise by as much as 6°C by the end of the century, higher than the Intergovernmental Panel on Climate Change (IPCC) predicts.


The new computer modelling looks at the effects of aerosols in the atmosphere, small particles and droplets in the air from combustion processes, chemicals and smoke.

Normally, aerosols act as a brake on the greenhouse effect. But as regulatory agencies issue new air purity controls, levels of aerosols will diminish.

This means that we will feel the effect of the climate change more strongly, the scientists argue.

"The actual true force of the greenhouse gases has been masked by the effects of the aerosols. They put a brake on warming and we don't really know how strong that brake is," says lead author of the paper, Professor Meinrat Andreae, from the Max Planck Institute for Chemistry in Germany.


Even hotter

The IPCC predicts the rise in global temperatures from a doubling of carbon dioxide could be in the range of 1.5 to 4.5°C by the end of the century.

But according to calculations by Andreae and his team, the figure could be as high as 6°C.

"That's quite a lot," says Andreae.

What do aerosols do?

Aerosols influence the atmosphere in many ways, but on balance, there is a cooling effect.

For example, they can block sunlight. They can also act indirectly, affecting cloud formation and rainfall.

But a combination of falling aerosol levels and their relatively short lifespan in the atmosphere will diminish the cooling affect, the scientists argue.

While aerosols stay in the atmosphere for about a week, greenhouse gases accumulate over about 50 years.

So the aerosol brake is going to come off faster than the decrease in greenhouse gases, the scientists say.

"Because one is cumulative and the other is not, the cumulative will always win out in the long run," says Andreae.
