China’s aggressive campaign to reduce air pollution has delivered dramatic improvements in public health and air quality over the past decade. However, new research suggests that the same policies may have unintentionally contributed to a small but measurable increase in global warming.
The study, published in Geophysical Research Letters, finds that sharp reductions in sulfur dioxide emissions from China have lowered atmospheric sulfate aerosols tiny particles that previously reflected sunlight back into space and exerted a cooling effect on the planet.
While the environmental and health benefits of cleaner air are undeniable, scientists say the climate system is responding in complex ways.
Decade of sweeping reforms
China launched its Air Pollution Prevention and Control Action Plan in 2013 in response to severe smog episodes that threatened public health and economic stability. Coal-fired power plants were retrofitted with scrubbers, heavy industries were modernized, and pollution standards were significantly tightened.
As a result, atmospheric particulate matter has fallen by more than 50%. Sulfur dioxide emissions, a major contributor to acid rain and smog, have dropped by roughly two-thirds.
The transformation has been described as one of the most significant air quality improvements in recent history.
However, sulfur dioxide does more than create smog. In the atmosphere, it reacts to form sulfate aerosols microscopic particles that reflect incoming solar radiation back into space. This reflection reduces the amount of heat absorbed by Earth’s surface, producing a cooling effect known as aerosol radiative forcing.
Scientists estimate that globally, aerosols have offset roughly one-third of the warming caused by greenhouse gas emissions.
With China cutting sulfur dioxide emissions, fewer sulfate aerosols are forming. That means less sunlight is reflected away from Earth and more energy is retained, contributing to warming.
Modeling in the new study suggests that declining sulfur dioxide emissions from China may have contributed approximately 0.06 to 0.07 degrees Celsius of global warming between 2007 and 2025. This accounts for about 12% of the total warming observed during that period.
Although tenths of a degree may appear small, climate scientists emphasize that even minor temperature increases can intensify extreme weather, accelerate sea-level rise and disrupt ecosystems.
Widespread atmospheric impacts
Using an advanced Earth system model combined with chemical observations collected by research aircraft over the Asian summer monsoon region, researchers examined how changes in emissions altered atmospheric composition.
They estimate that between 2010 and 2020, Chinese emissions reductions lowered sulfate aerosol concentrations by more than 20% over the North Pacific and by over 7% near the tropics.
These declines increased global net radiative forcing by approximately 0.10 to 0.15 watts per square meter, with some regional effects up to six times stronger.
Although aerosol decreases were largest in the upper troposphere, sulfate particles in the stratosphere can remain suspended longer, allowing their climatic influence to spread over larger areas and persist for extended periods.
The majority of the radiative impact was driven by shortwave effects both direct reflection of sunlight and indirect interactions with clouds, where aerosols influence how droplets and ice crystals scatter solar radiation.
The study also highlights the complex interactions across Asia. While China’s sulfur emissions have fallen sharply, emissions in India have increased during a similar period. These opposing trends are reshaping the regional aerosol balance in complicated and sometimes offsetting ways.
Because both countries strongly influence the chemical composition of the Asian upper troposphere and lower stratosphere, changes in emissions can affect atmospheric chemistry, radiation patterns and climate far beyond national borders.
Pollution cuts remain essential
Researchers stress that this finding does not mean air pollution was beneficial. Sulfate aerosols provide temporary cooling, but they come at severe costs to human health, ecosystems and infrastructure.
Importantly, aerosols are short-lived, remaining in the atmosphere for days to weeks. In contrast, greenhouse gases such as carbon dioxide and methane can persist for decades or even centuries.
This means the long-term trajectory of climate change is still driven primarily by greenhouse gas emissions. Cutting carbon dioxide and methane remains the most critical step in stabilizing global temperatures.
The study underscores the need for climate models to accurately account for the shifting balance between cooling aerosols and warming greenhouse gases. As countries continue to clean up air pollution while pursuing decarbonization, understanding these interactions will be essential for accurate climate forecasting and effective policy decisions.
China’s success in reducing smog stands as a major public health achievement. But the research makes clear that in the interconnected climate system, even positive environmental actions can produce complex and sometimes unexpected global consequences.