Chinese leaders, grappling with some of the world's worst air pollution, have long assumed the answer to their woes was gradually reducing the level of smog-forming chemicals emitted from power plants, steel factories and cars.
Changing weather patterns linked to rising global temperatures have resulted in a dearth of wind across northern China, according to several recent studies, exacerbating a wave of severe pollution that has been blamed for millions of premature deaths. Wind usually helps blow away smog, but changes in weather patterns in recent decades have left many of China's most populous cities poorly ventilated, scientists say.
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The findings, some of the first to link climate change to smog, may escalate pressure on Chinese leaders to move more swiftly to shutter steel factories and coal-fired power plants amid rising public anger over smog caused by soot and gases like sulfur dioxide. The research could also push China to assume an even more forceful role in international efforts to curb climate change by reducing carbon emissions, at a time when the United States, under President Trump, appears to be backing away from the issue.
"Everyone used to think that controlling smog hinged on reducing regional pollution," said Liao Hong, a professor at Nanjing University of Information Science and Technology and the co-author of a climate change study published this week. "Now it's clear that it will require a global effort."
As public outrage has grown in China over dirty skies and a rash of respiratory illnesses linked to smog, Chinese officials have redoubled efforts in recent years to fight air pollution. They have dispatched teams of police officers to inspect factories, closed down hundreds of coal-fired power plants and imposed limits on driving and activities like outdoor barbecuing.
Premier Li Keqiang, speaking at the annual session of China's legislature this month, vowed to "make our skies blue again" and promised to take further steps to reduce the use of coal.
But even if Chinese officials push forward with ambitious plans to cut emissions, they may struggle to offset the effects of climate change, the findings suggest.
Ms. Liao's study, which examined data on pollution in Beijing from 2009 to 2016, predicted that weather conditions associated with severe smog would become increasingly common in coming decades. The study did not account for possible reductions in carbon emissions under the 2015 Paris Agreement on climate change.
Scientists point to the so-called airpocalypse that fell on Beijing in January 2013 as an example of the effects of climate change on smog.
During that episode, Beijing and dozens of other cities in northern China were shrouded in toxic haze for days. Despite emergency measures to cut emissions, the concentration of PM2.5, particles of a size that can penetrate the bloodstream, remained dangerously high.
Researchers now attribute the resilience of smog during that period to unusually stagnant air conditions brought on by climate change. The air was the stillest in three decades during the heavy particulate pollution in 2013, according to a study published this month in the journal Science Advances.
The study found that the melting of ice in the Arctic, combined with increased snowfall in Siberia, contributed to changes in wind patterns across Asia that winter that failed to clear the air over northern China.
Yuhang Wang, an atmospheric scientist at Georgia Institute of Technology in Atlanta who was a co-author of the study, said the results suggested that Chinese officials would have an especially difficult time curbing air pollution in the winter, when weather conditions are most conducive to smog and more coal is burned for heating. The Ministry of Environmental Protection pledged this month to put in place stricter policies to curb winter air pollution. Beijing is set to host the Winter Olympics in 2022.
"In the long run, emission reductions of both pollutants and greenhouse gases are needed to mitigate the winter haze problem," Mr. Wang said.
The effect of climate change on air pollution might extend beyond China. In a study last year, for example, Mr. Wang found that warmer and drier conditions might lead to longer stretches of ozone pollution in parts of the southeastern United States. (Previous studies have also shown a link between climate change and ozone pollution.)
The Chinese government has emerged as one of the leading voices on fighting climate change. As the Trump administration hints that it might move away from international efforts to cut emissions, environmentalists are looking to China, the world's largest emitter of greenhouse gases, to play a leading role in curbing the use of fossil fuels.
The government has pledged to go more aggressively after polluters and to cut excess production in heavy industry. Already, some progress has been made, with particulate pollution falling nearly 10 percent in the Beijing area over the past three winters, according to government statistics.
But many cities, especially in the north, continue to experience severe bouts of smog, resulting in school closures, traffic accidents and increases in hospital visits. Enforcement of environmental laws remains lax, and steel capacity actually rose last year, contributing to a surge in air pollution, a Greenpeace report found.
The growing body of research on the links between climate change and air pollution might serve as a rallying cry for China to take a more aggressive role in cutting greenhouse gas emissions. But it could also give the government another excuse for the country's pollution problems, analysts said.
"In light of growing local protests against poor air quality, linking this issue with climate conditions outside of China underscores the fact that the pollution problem has international sources in addition to local," said Marc Lanteigne, a senior lecturer on Chinese defense and security issues at Massey University in New Zealand.
Environmentalists said the role of climate change in exacerbating smog was an important finding. But they underlined the need for local governments to do more to reduce emissions.
"It won't change the overall conclusion that air pollutant emission is the direct and interior cause for this air pollution problem," Dong Liansai, a climate and energy advocate at Greenpeace in Beijing, wrote in an email. "Much more action is required."