Adapted from a release published by the Center for International Climate Research.

The cleanup of air pollution in East Asia has accelerated global warming, a new study in the journal Communications Earth and Environment has found. That’s because some forms of air pollution in the atmosphere have helped shade the Earth’s surface from the sun’s energy.

The rate of global warming, driven primarily by greenhouse gas emissions, has been accelerating for the past 15 years and has led to record-breaking surface temperatures.

Over the same period, countries in East Asia, particularly China, implemented aggressive air quality policies that led to about a 75% reduction in sulfur dioxide (SO₂) emissions. These policies have been important public health wins: in China, for example, ambient air pollution is responsible for more than a million deaths per year.

But as countries have gotten better at reducing air pollution, they’ve also inadvertently unmasked global warming, says co-author Daniel Westervelt, an associate research professor at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School.

“Many aerosol particles emitted from human activity reflect incoming sunlight and have a surface cooling effect,” says Westervelt. “As their concentrations decrease in the atmosphere, our research shows that can play a leading role in recent warming.”

The team used climate model simulations to isolate the role of aerosol reductions in recent temperature trends.

“We have been able to single out the climate effects of air quality policies in East Asia over the last 15 years,” says Bjørn H. Samset, lead author and senior researcher at CICERO Centre for International Climate Research. “Our main result is that the East Asian aerosol cleanup has likely driven much of the recent global warming acceleration and also warming trends in the Pacific.”

Analyzing the climate effects of emissions from a single region is challenging. It requires climate simulations that have not been readily available and updated emissions data that captures the actual pollution reductions in and around mainland China. Using a large set of simulations from eight different climate models, the researchers show how the 75% reduction in East Asian sulfate emissions partially unmasks greenhouse gas-driven warming and alters how temperatures rise in different parts of the world.

The study also explores how long the warming effects from reduced aerosols are expected to last.

“The climate effects of air pollution are short-lived, while the impact of carbon dioxide emissions can be felt for centuries,” says co-author Laura Wilcox, who is an associate professor at the University of Reading’s National Centre for Atmospheric Science. “This means that the acceleration of warming due to reductions in air pollution is also likely to be short-lived. We will see an acceleration of warming while the unmasking takes place, and then a return to a greenhouse gas-driven rate of warming as air pollution stabilizes.”

Additional Columbia co-authors include climate scientists Kostas Tsigaridis and Larissa Nazarenko, from the Center for Climate Systems Research.

Press interviews with Daniel Westervelt and other authors can be arranged by emailing press@climate.columbia.edu.