Does pollution keep Earth cool? New study says global warming may be linked to pollution cuts

A surprising new study has found that a major portion of recent global warming may not be due to rising carbon dioxide emissions alone but to the success of air pollution control efforts, particularly the reduction of sulphur dioxide (SO₂) in the atmosphere.

According to preliminary findings presented by climate scientists Peter Cox and Margaux Marchant from the University of Exeter, nearly two-thirds of global warming since 2001 could be linked to reductions in SO₂ pollution rather than increases in carbon dioxide (CO₂). Their analysis, based on satellite observations from 2001 to 2019 shows that Earth’s ability to reflect sunlight—its albedo has decreased, primarily due to changes in cloud brightness.

“Clouds have become darker and less reflective as SO₂ levels have declined,” said Cox. “That’s making the planet absorb more sunlight, leading to more warming.”

The study focuses on data from NASA’s CERES satellite instruments, which track how much sunlight the Earth reflects versus how much it absorbs. These measurements have shown a noticeable fall in reflected sunlight over the past two decades, suggesting the planet is effectively becoming darker. While declining snow and sea ice, as well as reduced cloud cover, are known contributors to this effect, Cox and Marchant identified dimmer clouds as the most significant factor.

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This dimming is closely tied to falling SO₂ emissions. Sulphate particles from industrial pollution and shipping previously made clouds brighter by increasing droplet density, an effect known as cloud albedo. But as high-sulphur fuels such as coal have been phased out and pollution controls tightened, particularly in East Asia, this brightening effect has diminished.

In essence, by cleaning the air, we have inadvertently turned down a natural form of solar reflectivity, leading to extra warming.

Laura Wilcox, associate professor at the National Centre for Atmospheric Science (NCAS) in the University of Reading said the findings align with her own work, which also suggests that recent accelerated warming is linked to declining air pollution. However, she cautioned that other studies point to a different mechanism, reduced cloud cover rather than dimmer clouds as the primary driver of the trend. “The causes of the recent darkening of the planet are still being debated,” she said.

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Despite some uncertainties, scientists say this explanation is reassuring. If the rapid warming were due to heightened climate sensitivity to CO₂, it would suggest a more alarming long-term trajectory. Instead, the pollution-linked warming effect is expected to be temporary.

“It’s a double-edged sword,” Cox noted. “Cleaner air is good for health and the environment, but we now need to adapt faster and double down on cutting greenhouse gases to offset the lost cooling effect of sulphate pollution.”

The findings highlight a delicate climate trade-off: as efforts to reduce harmful air pollution succeed, the urgency to address CO₂ emissions becomes even more critical.