How clean-air efforts may have exacerbated global warming

Scientists have struggled to explain the rapid acceleration of global warming over the past 15 years, with temperatures now regularly breaking records.

It is “among the biggest questions in climate science today”, said atmospheric science professors Laura Wilcox and Bjørn H. Samset on The Conversation. Causes suggested by researchers include a clean-up of sulphur emissions from global shipping, as well as changes in cloud cover.

But “one factor that has not been well quantified” are the “monumental efforts” by east Asian countries, particularly China, to combat air pollution. A recent study by Wilcox and Samset claims that east Asia’s “aerosol clean-up” is likely a “key reason” for the surge. The polluted air “may have been masking the full effects of global warming”.

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The ‘sting in the tail’

“In the early 2000s, China had extremely poor air quality as a result of rapid industrialisation, leading to a public outcry in the run-up to the 2008 Beijing Olympics,” said New Scientist.

In response, Beijing began concerted and highly effective efforts to reduce air pollution. But “there is a sting in the tail of this environmental success story”. Its dirty air had “inadvertently been cooling the planet”.

Reducing air pollution didn’t actually cause additional warming – but it “removed an artificial cooling”, said Wilcox and Samset on The Conversation. Air pollution “shields the Earth from sunlight and therefore cools the surface”. The aerosol particles reflect sunlight into space or influence cloud formation so that they reflect more sunlight. But reducing air pollution means removing “this artificial sunshade”. Since China’s greenhouse gas emissions (the main driver of global warming) continued to increase, “the result is that the Earth’s surface is warming faster than ever before”.

More good than harm

“When we started looking at the numbers, it turns out it is definitely macroscopic – it’s not a small effect,” Samset told New Scientist. China’s air pollution crackdown is responsible for 80% of the increased rate in global warming since 2010, the team concluded.

“When you emit aerosols over China, they are taken by the atmospheric circulation, transported out over the Pacific, so they spread over a large area,” said Samset. “The same amount of emissions from India would not have had the same effect on global warming.”

But the action still did more good than harm, said Duncan Watson-Parris, of the University of California San Diego. “The consequence for the climate is not great, but it’s not as acute as the number of people that were dying because of air quality.”

Air pollution is still a major concern in China, however. It’s responsible for about two million deaths a year, according to the World Health Organization. This year Beijing is “ramping up efforts in pollution control and emissions reduction” in a bid to eliminate it by the end of 2025, said The Independent.

“The battle for blue skies remains unchanged,” said a senior environment official, Li Tianwei.