China's 'airpocalypse' linked to Arctic sea ice loss

http://www.bbc.co.uk/news/science-environment-39279500

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The air pollution that lingered over eastern China for nearly a month in 2013 has been linked to the loss of Arctic sea ice the previous autumn.

A study says the haze lasted much longer because the melting ice and increased snowfall altered wind circulation patterns.

If Arctic ice continues to shrink due to climate change, the scientists say similar events will likely recur.

They argue that this could threaten the Beijing Winter Olympics set for 2022.

Emissions puzzle

Air quality issues have plagued China in recent years but the pollution experienced in January 2013 was significant because it lasted so long.

The large-scale haze stayed in place for almost a month and around 70% of China's 74 major cities exceeded the daily air quality standard for very fine particulate matter, which poses serious risks to health.

Scientists were puzzled by the event as the Chinese government had taken steps to curb emissions from coal fired power plants, one of the most significant contributors to air pollution.

Now researchers say that record Arctic sea ice decline in late 2012, plus extensive snowfall over Siberia disturbed wind patterns and produced stagnant air conditions over the east China plain.

"In wintertime, in regions like Beijing you get these north west howling winds that blow like hell," said Prof Yuhang Wang from Georgia Tech University, one of the report's authors.

"A ridge system controls the intensity and location of this cold air moving south so what happens when you put in sea ice forcing or snow forcing, the ridge system gets weaker and moves eastward - instead of cold air blowing in the eastern part of China, it went to Korea and Japan in January 2013."

The research team looked at ventilation conditions over the past 35 years and were able to show that the poor dispersal seen in 2013 was unique.

They then looked at the climate related factors that might contribute to poor ventilation and their findings indicate that the loss of Arctic ice and snowfall over the forests of Eurasia were critical for the haze event.

The researchers weren't able to separate the scale of the impacts between these two factors. What they are sure about is that in combination, they made the haze much worse.

"You see evidence in the summer that the particulate matter is getting less, but you don't see a clear trend in the winter and what we believe is that the effort is being hammered by changes in the Polar region with ice and snow," said Prof Wang.

The researchers say that global climate change will likely ensure that Arctic sea ice continues to decline and maintain the conditions for haze events.

They say this could threaten the Beijing Winter Olympics in 2022 which will take place across a large geographical area. In their view it poses a greater threat to these future games, than dirty air did to the summer games in 2008.

"Had the Chinese government not reduced emissions as much as they did in the last four years we would have seen the same or worse airpocalypse events," said Prof Wang.

"We haven't seen it as much because of these emissions reductions and the study shows that if you want to clean up air during the Olympics they have to cut emissions even more drastically than they expected before."

The authors say that while China can take more steps to curb particulate matter, curbing the greenhouse gases that are helping to shrink Arctic sea ice, will take a global effort.

The study has been published in the journal, Science Advances.

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