The world’s cities aren’t just hotspots of population growth and commercial activity. They are also, literally, hot spots. The urban “heat island” effect—i.e., concentrated heat in urban environments—is serious enough that cities worldwide could suffer double-digit temperature increases and lose as much as 11% of their economic output as their residents flee stifling heat, according to a new study published in the journal Nature Climate Change.
The study’s authors, who were from Great Britain, Mexico, and the Netherlands, surveyed 1,692 cities worldwide and forecasted that 25% of them could undergo temperature increases of up to 44.6 degrees Fahrenheit by 2100 under the worst-case scenarios.
Climate change exacerbates the heat island effect. But the phenomenon’s underlying drivers are the concrete, stone, and asphalt surfaces that constitute modern city structures. These surfaces absorb large amounts of energy from the sun. Cities could mitigate the heat rises if they redesign roofs and pavements to reflect more of the sun’s heat, the authors suggested.
Cities’ heat-trapping effects are nothing new. The authors noted that from 1950 to 2015, 27% of the world’s cities warmed more quickly than the planet as a whole—and that 27% accounted for more than 65% of the world’s urban population.
If trends continue, the worst-affected cities could be 44 degrees hotter as soon as 2050, the researchers warn. But they also found that changing just one-fifth of a city’s roofs or half its pavements to “cool” versions that reflect sunlight could prevent as much as 33 degrees of this worst-case increase.
“We show that city-level adaptation strategies to limit local warming have important economic net benefits for almost all cities around the world,” said co-author Richard Tol of Sussex University.