In 2013, China launched an ambitious campaign to clean up its air. Cities like Beijing, once blanketed by thick industrial smog, began to see blue skies. Sulphur dioxide levels across East Asia dropped by approximately 75 percent over the following decade. It was a global public health victory, saving lives and improving daily life for millions.

But this dramatic improvement came with a surprising side effect. Scientists now say that the smog, harmful as it was, had also served as a kind of sunshade. Aerosol pollution reflected sunlight away from Earth and helped cool the planet’s surface. Once that layer was removed, the warming became more apparent.

According to a new study by researchers from the University of Reading and CICERO, reductions in air pollution may have accelerated global warming. Drawing on 160 simulations from eight global climate models, the research points to a key factor behind why global temperatures have risen faster than expected since 2010.

Aerosols masked the heat—until they didn’t

For decades, aerosols such as sulphur dioxide unintentionally helped mask the full force of human-caused climate change. These particles reflect sunlight and lead to the formation of brighter, longer-lasting clouds. Altogether, they’re estimated to have reduced global temperatures by about 0.5°C (0.9°F) over the last century.

That cooling, however, was always temporary. Aerosols remain in the atmosphere for only days or weeks, unlike greenhouse gases that can linger for centuries. Once pollution levels fall, their masking effect fades quickly.

Since 2010, Earth’s average temperature has increased by about 0.33°C (0.59°F). Based on greenhouse gas trends alone, scientists expected an increase closer to 0.23°C (0.41°F). That 0.1°C (0.18°F) discrepancy raised questions. This new research suggests that roughly 0.07°C (0.13°F) of the excess warming can be traced to reduced aerosol emissions from East Asia.

Other contributors likely include the recent rise in atmospheric methane and changes in global shipping regulations that further cut sulfur emissions.

One of the most telling findings came from satellite data. As aerosol pollution dropped in East Asia, so did the region’s cloud cover over the North Pacific. That allowed more sunlight to reach the ocean, amplifying warming in areas downwind of the pollution cuts.

Clean air didn’t just help people breathe more easily. It also pulled back a veil, revealing the true pace of global warming.

What it means for climate policy

China’s air cleanup was essential. Sulphur dioxide and other pollutants contribute to respiratory illnesses, heart disease, and millions of premature deaths worldwide. But as the pollution dropped, it also removed a buffer that had partially muted the full effects of greenhouse gas emissions.

This doesn’t mean the cleanup caused global warming. Rather, it exposed warming that had been temporarily obscured. The root driver of climate change remains fossil fuel use and the long-lived greenhouse gases it releases.

The findings emphasize that clean air policies and climate action must go hand in hand. If we eliminate aerosol pollution without simultaneously cutting greenhouse gas emissions, we may see sharper, more sudden spikes in warming.

To manage these risks, governments must prioritize faster reductions in methane, invest in carbon removal strategies, and accelerate the global shift to clean energy. These steps aren’t just about long-term sustainability—they’re immediate tools to manage a climate that no longer benefits from the dimming effect of dirty air.

For years, aerosol pollution distorted our understanding of what global warming truly looks like. Now that the skies are clearing, the full picture is coming into view—and it’s heating up quickly.