Climate Change Worsening China’s Winter Smog

A photo taken in the city of Taiyuan, China shows haze on Dec. 3, 2016. (Credit: Yuhang Wang)

(CN) – China may be able to blame its severe air pollution problems – at least in part – on the wide-ranging effects of global climate change.

In a new study published in the journal Science Advances, researchers at the Georgia Institute of Technology suggest that snowfall and sea-ice changes have thrown off China’s winter monsoon, leading to stagnant atmospheric conditions that trap pollution above the nation’s major industrial and population centers.

Stemming from Arctic sea-ice loss and increased Eurasian snowfall – both of which are caused by climate change – these changes in regional atmospheric conditions are hampering China’s efforts to address pollution through emission controls.

“Emissions in China have been decreasing over the last four years, but the severe winter haze is not getting better,” said Yuhang Wang, a professor at Georgia Tech. “Mostly, that’s because of a very rapid change in the high polar regions where sea ice is decreasing and snowfall is increasing. This perturbation keeps cold air from getting into the eastern parts of China where it would flush out the air pollution.”

The new research highlights the significant regional impacts produced by climate change, according to the team. The findings are believed to be the first to connect sea ice and snowfall levels to regional air pollution.

Haze above the East China Plains – which include the capital, Beijing – first attracted worldwide attention during the winter of 2013, when an instrument at the U.S. embassy recorded unusually high PM 2.5 particles, which is an air pollutant that can affect human health. This prompted the Chinese government to institute strict targets for curbing emissions from industry and other sources.

Though the efforts appear to be working, the haze problem continues.

In order to determine if other factors may be playing a role, the team pieced together estimates based on visibility measures and satellite data. To analyze the historical records, the researchers created a new Pollution Potential Index, or PPI, which used air temperature gradient anomalies and surface winds speeds as a substitute for ventilation conditions over eastern China.

“Once we generated the PPI and combined it with the visibility data, it was obvious that January 2013 was well beyond anything that had ever been seen before going back at least three decades,” Wang said. “But in that month emissions had not changed, so we knew there had to be another factor.”

The East China Plains are significant to the United States as the interconnected basins surrounded by mountain ranges to the west, and the ocean to the east, mirror Southern California. Pollution created by industry and vehicles can be removed effectively only by vertical mixing in winter and horizontal dispersion. When those processes fail to shuttle stagnant air, pollution builds up.

The team reviewed climate features like sea ice, snowfall and El Nino, and conducted analyses that found correlations between stagnant air conditions over China and Arctic sea ice, which reached a record low in the fall of 2012. The researchers also measured snowfall in the upper latitudes of Siberia, which hit a record high earlier in the winter. They then used atmospheric model simulations to determine how these factors change large-scale circulation patterns and pollution ventilation over eastern China.

“The reductions in sea ice and increase in snowfall have the effect of damping the climatological pressure ridge structure over China,” Wang said. “That flattens the temperature and pressure gradients and moves the East Asian Winter Monsoon to the east, decreasing wind speeds and creating an atmospheric circulation that makes the air in China more stagnant.”

The findings are consistent with observations that South Korea and Japan had been unusually cold that winter, while eastern China had been unusually warm – suggesting the cold center had moved.

The same factors occurred this winter, with low levels of Arctic sea ice in September 2016, high snowfall and severe haze. Wang says those these factors will likely continue as climate change disrupts the normal structure of the atmosphere.

“Despite the efforts to reduce emissions, we think that haze will probably continue for the future,” Wang said. “This is partly climate-driven now, so it probably won’t get much better in the winter. Emissions are no longer the only driver of these conditions.”

Wang said the impact of climate change may be unique to China due to its geography and sensitivity to atmospheric circulation structure. While the problem is now affecting air pollution, he said the results of the study should motivate the nation to continue addressing the climate change.

“The very rapid change in polar warming is really having a large impact on China,” he said. “That gives China an incentive to not only follow through on air pollutant emission reductions, and also to look at the potential for reducing greenhouse gas emissions.”