Urban heatwaves are accelerating for a surprising reason

Heatwaves are getting worse. That’s not new. But a less obvious reason for the rise in extreme heat, especially in cities, might be catching scientists and local governments off guard.

It turns out that a major driver of these heatwaves isn’t just greenhouse gases. It’s the steady decline of something we’ve spent decades trying to eliminate: air pollution.

Smog cuts raise urban heat

A new study from scientists at The University of Texas at Austin shows that falling levels of aerosols – tiny particles that contribute to smog and haze – are playing a much bigger role in extreme heat than previously thought.

The researchers found that in populated areas, aerosols are up to 2.5 times more influential than greenhouse gases in driving changes in heatwave exposure.

While earlier research had connected aerosols to regional temperature patterns, this is the first study to look specifically at how those changes affect the number and intensity of heatwaves that people actually experience.

“Heatwaves near urban centers was much greater than we expected,” said study co-author Cameron Cummins. “So, as cities seek to curb their aerosol emissions to improve public health, they will also likely experience more heatwaves.”

Cleaner air, hotter cities

Using global climate models, the researchers analyzed aerosol trends from 1920 to the present. They found that in cities and other populated regions, higher levels of aerosols helped cut heatwave exposure by nearly half.

That’s because aerosols can reflect sunlight, essentially shielding certain areas from the full brunt of global warming. But here’s the catch: those protective aerosols are disappearing.

As countries around the world pass clean air regulations to improve health and reduce pollution, aerosol levels are dropping. This is good news for our lungs – but it also means the natural “shade” they provided is vanishing fast.

“Aerosols are really good at counteracting exposure [to heatwaves] right now, but that could rapidly change in the future,” said Geeta Persad, who led the study.

“We seem to have already crossed a tipping point where declining aerosols are accelerating heatwave exposure in a lot of places.”

More heatwaves on the way

If aerosol emissions continue to decline at the current pace, the effects could be dramatic. The researchers project that by 2080, the average number of heatwave days globally could nearly triple – from about 40 days a year to 110.

Regions most likely to be affected include Sub-Saharan Africa, South Asia, South America, and Western Europe.

In this study, a heatwave is defined as three or more consecutive days during a region’s warm season that exceed the 90th percentile for temperature.

Sustained heat like this strains power grids, worsens health risks, and pushes infrastructure to its limits.

Not all emissions are the same

Aerosols and greenhouse gases often come from the same sources – such as burning fossil fuels – but they behave very differently.

Greenhouse gases trap heat, disperse globally, and can stay in the atmosphere for decades or even centuries. Aerosols, by contrast, have a short lifespan. They tend to stay localized and usually fall out of the air in a matter of weeks.

That short-term impact means we can see the effects of reduced aerosols quickly – which is good for health but risky for heat. Persad emphasized that this makes cities especially vulnerable as they clean up their air.

Urban heatwaves surge without aerosols

Western Europe is a clear example. In the latter half of the 20th century, high aerosol levels helped shield the region from heatwaves, even as greenhouse gas concentrations climbed – but that’s changing.

The study showed that in just the next 25 years, reduced aerosols could lead to as many as 40 extra heatwave days per year in urban parts of Western Europe. Still, the researchers aren’t calling for a return to dirtier air. Far from it.

“The study results shouldn’t be taken as a license to pollute,” said Persad. High aerosol levels are dangerous. They contribute to respiratory and cardiovascular problems and cause thousands of premature deaths every year.

“This work suggests that what happens with aerosols in the near future is going to be really important for what happens with heat wave hazard and exposure and risk in the near future, the next 20 to 30 years.”

What cities can do

The key takeaway? Cleaner air is non-negotiable, but it comes with trade-offs. As we cut pollution, cities need to be ready for more intense heat.

That means planning for infrastructure that can handle heatwaves, updating emergency response systems, expanding access to cooling centers, and rethinking urban design – all while continuing to fight climate change on a global scale.

Cleaner air is saving lives. But without better preparation, it could also mean hotter days ahead.

The full study was published in the journal Environmental Research Letters.

—–

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.

—–