China’s fight against smog has actually sped up global warming

For most of the 2000s, climate scientists could draw a fairly straight line through Earth’s rising temperature curve. The world was warming, yes, but the pace was predictable – until it wasn’t.

Sometime around 2010, the slope steepened, and over the past 15 years, the thermometer has shot up faster than many forecasts had anticipated.

After back-to-back record-shattering years in 2023 and 2024, researchers began hunting for a hidden driver of warming and found an unexpected culprit: smog over East Asia had cleared too quickly, removing a key layer of atmospheric protection.

“When something like the anomalous, record‑breaking warmth of 2023 and 2024 happens, climate scientists start to wonder if there’s a factor we’re missing,” said co-author Robert Allen, a climatologist at the University of California, Riverside. “This study was our effort to figure out what that might be.”

Allen teamed up with Bjørn Samset from Norway’s Center for International Climate and Environmental Research and dozens of colleagues worldwide to run eight state‑of‑the‑art climate models through thousands of simulated futures. All roads pointed back to tiny, sun‑scattering particles called aerosols.

From choking smog to clear skies

Aerosols – think sulfate haze from coal smokestacks or the soot in diesel exhaust – cool the planet by reflecting sunlight and seeding bright, reflective clouds.

East Asia, and China in particular, pumped vast quantities of these particles into the atmosphere during its early‑2000s industrial boom.

Then, in response to dire health statistics, Beijing launched an aggressive clean‑air campaign. Between 2010 and 2020, sulfur dioxide emissions, a major source of sulfate aerosols, fell by roughly 75 percent.

In human terms, the smog cleanup is an unambiguous win; air pollution once killed more than a million Chinese citizens each year. In climate terms, though, it removed a temporary sunshade.

Fewer reflective particles meant more solar energy reached Earth’s surface, especially over the Northern Hemisphere. “The spike in warming aligns with a dramatic drop in aerosol pollution from China’s skies,” Samset said.

Smog reduction drives warming surge

The models suggest that East Asia’s reduced smog and clearer air added about 0.05 °C of extra warming per decade – enough to account for most of the acceleration since 2010, even after natural swings like El Niño are removed.

That figure might feel small, but in a world already teetering near 1.5 °C above pre‑industrial averages, every hundredth of a degree matters. Extreme heat waves become more frequent, glaciers melt faster, and coral reefs suffer additional bleaching.

And the effects are not confined to East Asia. Atmospheric circulation spreads heat anomalies around the globe. The United States and Europe, for example, endured record‑breaking summers in 2023 partly because the planet as a whole was running warmer than usual.

Cleaning air isn’t enough

Allen calls the situation a cautionary tale. “Reducing air pollution has clear health benefits, but without also cutting CO2, you’re removing a layer of protection against climate change.”

In other words, focusing on smog particles while ignoring greenhouse gases is like taking off a pair of sunglasses and stepping into brighter light. The glare returns instantly because aerosols live only about a week in the lower atmosphere.

“Sulfur dioxide and sulfate aerosols have lifetimes of about a week. Once they’re removed, we’ll eventually settle back into a warming rate that’s more consistent with the long‑term trend,” Allen explained. Yet the planet must first absorb that short‑term pulse of extra heat.

Samset stresses that carbon dioxide and methane remain the main villains. “Our study focused on the recent, dramatic speedup in global warming, which is very concerning but still small compared to the overall, long‑term amount of warming from increased CO2 and methane.”

Both gases linger for decades or centuries, meaning their warming power is cumulative and relentless.

More smog cleanups, more warming

China is not alone. India, parts of Africa, and even the United States continue to tighten air‑pollution rules.

RAMIP – the Regional Aerosol Model Intercomparison Project that supplied data for the current paper – plans to test how simultaneous clean‑ups might rewrite near‑term climate projections. Early hints suggest the global thermometer could tick upward even faster unless greenhouse‑gas cuts accelerate in parallel.

The dilemma has revived interest in geoengineering schemes that would mimic the cooling effect of aerosols by spraying reflective particles high into the stratosphere.

Allen urges extreme caution: “It’s a card we might have to play if we’re pushed into a corner,” he acknowledged, “but it comes with a host of risks, including disrupted rainfall patterns, food insecurity, and political tensions.”

Unlike accidental pollution, engineered aerosols could be difficult to govern and almost impossible to stop quickly without triggering a sudden rebound in temperatures.

Both battles must be fought

For now, the lesson is clear. “Air quality improvements are a no‑brainer for public health,” Allen said. “But if we want to prevent the worst impacts of climate change, we have to cut CO2 and methane too. The two must go hand in hand.”

Cleaner skies have bought East Asia healthier lungs and bluer horizons. They have also revealed, in stark relief, the heat still trapped by our greenhouse gas emissions.

Ultimately, as the world works to end one environmental crisis, it cannot afford to ignore the other.

The study is published in the journal Communications Earth & Environment.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–