Some of the world’s biggest cities are so polluted they’re warming slower

The question of whether global warming is accelerating is hotly contested among climate scientists. While some have argued that the current rate of warming — which hit an all-time high last year — is strictly correlated with increased fossil fuel emissions and therefore aligned with current climate models, others have cautioned that the Earth is far more sensitive to fossil fuels than previously thought and that humanity is hurtling toward tipping points from which there can be no return. 

In a recent study, a group of researchers from the University of Melbourne complicated this debate with an analysis of warming rates across the globe and possible causes for regional differences. Their principal finding: The globe is getting hotter at a faster rate, but this acceleration is occurring unevenly. Surprisingly, densely populated areas with large concentrations of poverty — megacities like Cairo and Mumbai — are warming more slowly than urban centers in Europe and North America. Why? The researchers found that the large quantity of aerosol particles in the air of highly polluted cities reflect sunlight back out into space and, at least in the short term, can have a net cooling effect on populations.

“It’s a brain-twister,” said Edith de Guzman, an adaptation policy specialist at the University of California at Los Angeles Luskin Center for Innovation, who commended the researchers for their work. The authors of the paper emphasized that the finding should hardly be taken as a good sign. For one, it’s likely only temporary. And secondly, the protection, such as it is, only comes from harmful pollutants. De Guzman concurred, saying accelerated warming means that “populations that are already grossly vulnerable to a variety of environmental and climate injustices will be more vulnerable.” 

As countries develop economically, their governments tend to adopt policies to clean up pollution, and as the air clears, vulnerable populations will be at a high risk of dangerous heat exposure. Christopher Schwalm, the Risk Program Director at the Woodwell Climate Research Center, offered the example of China, where the government has begun to equip its coal-fired power plants with emissions reduction technologies like scrubbers, to prevent soot from escaping the facility. Such measures are good for the quality of the air, he said, but they will allow more heat from the sun to seep in. The hardest hit will be those without access to air conditioners and shaded areas. 

“The poorer you are the hotter it gets, where heat is a metaphor for all forms of climate disruption,” Schwalm said. “It’s really hard to do good for not doing bad.”

Schwalm explained that the scientific community has about three dozen highly sophisticated climate models that are collectively thought of as a “panel of experts” on the trajectory of global warming. He believes that examining accelerated warming is useful because it can help countries plan for climate adaptation measures and understand how realistic their current climate policy goals are — or aren’t. 

Last year, the world blew past the emissions targets from 2015’s Paris Agreement, and is on track to do the same this year. Scientists are increasingly vocal about the so-called death of the Paris Agreement’s commitment to keep the world below a temperature increase of 1.5 degrees Celsius (2.7 degrees Fahrenheit), in attempts to force policymakers to contend with the inevitability of worsening heat waves and extreme weather events to come. 

The authors of the Melbourne paper offer much-needed insight about what that future will look like and how nations should prepare: Their findings should encourage “targeted climate adaptation strategies” directed at the poorest urban communities around the world.