The architectural, transportation, and energy systems of U.S. cities were built to withstand the climate of the mid-20th century, and that climate is gone, according to researchers interviewed in a Wall Street Journal report published Wednesday.
“A lot of infrastructure we’re still using now was built for the weather of the 1950s and ’60s,” said Costa Samaras, a professor of civil and environmental engineering at Carnegie Mellon University. “This is not the weather that we have now, and it’s not the weather that we’ll have in the future as it continues to be altered because of the emissions that lead to climate change.”
The key metric that cities will need to watch, researchers said, is the wet-bulb temperature—a measure that combines heat and humidity. When the wet-bulb temperature exceeds 87 degrees Fahrenheit (roughly 100 degrees Fahrenheit with a relative humidity of 60%), the human body can no longer shed heat efficiently, leading to heat stroke and organ failure.
“That is the combination of temperature and humidity that’s effectively unsurvivable,” said Brian Stone Jr., a professor at the Georgia Institute of Technology who directs its Urban Climate Lab. Stone said his research shows that U.S. cities have been nearing that threshold in recent years and that he expects Kansas City, Chicago, and Dallas to exceed it within three to five years.
“We’re moving into a world where we’re going to have shelter-in-place orders in heat waves, and we won’t be able to do outdoor work like garbage collection,” he said. “It’s a big issue. We’re very close to this threshold, and most people don’t even know that threshold exists.”
Beyond heat, a warmer climate intensifies storms, flooding, drought, and wildfires. To keep power flowing during the strain of peak demand, Samaras described emerging “grid-enhancing technologies” that use artificial intelligence. Sensors on power lines and in wind-turbine gears could feed data to machine-learning systems that predict neighborhood-level demand, measure line capacity, and shunt electricity from overloaded circuits to underused ones, he said.
Stone’s Urban Climate Lab has begun mapping intra-city heat variation, finding dramatic differences. In Atlanta, he said, one neighborhood can be 10 to 15 degrees hotter than another, driven by the “urban heat island” effect—heat-absorbing asphalt, concrete, and waste heat from cars and air conditioning. More detailed mapping would allow planners to test solutions such as tree planting, reflective surfaces, and green roofs on a block-by-block basis, he said.
Kathleen Merrigan, executive director of the Swette Center for Sustainable Food Systems at Arizona State University, envisions neighborhoods becoming “agrihoods” built around working farms on vacant lots, in city parks, on new housing developments, or as intensive rooftop farms. Although such small-scale farms could not replace large rural agriculture, she said they would cushion cities when floods or wildfires disrupt the broader food supply chain and would add green space that reduces the urban heat island effect.
Flash floods are also expected to intensify. “The expectation in the climate risk models is that there will be more precipitation when we don’t need it and less when we do,” said Joyce Coffee, president and founder of Climate Resilience Consulting in Chicago. Flood barriers, she said, tend to simply push water elsewhere. A better approach, she said, is to build rain gardens and bioswales—sunken planted areas that absorb excess stormwater. Coffee pointed to a basketball court in the Netherlands that doubles as a giant storm drain; seating around the court channels rainwater into a cistern underneath.
As heat waves grow longer and more frequent, public transportation will also need to be rethought. “We’ll definitely see an increased focus on the resilience of public transport,” said Cassie Sutherland, managing director for climate solutions and networks at C40 Cities, a global network of mayors working on climate policy. She cited reflective pavements, green corridors of shade trees along walking and cycling routes, and apps that show commuters the coolest route rather than the fastest. Reducing the number of gasoline-powered cars on the road is central to the effort, she said.
Stone said that some cities will eventually need to make far more radical changes, including relocating residents and businesses from entire neighborhoods and using the emptied land to build levees, green spaces, or fire breaks. He called this “retreat to adapt” and said it would affect properties that have flooded repeatedly.
“There are some properties in the United States that have flooded more than 30 times, and we have continued to rebuild them,” he said. “In a future of more extreme weather, that just becomes economically nonviable pretty quickly.”
He suggested that instead of rebuilding Pacific Palisades after wildfire, the area could have been turned into a giant fire break to protect the rest of Los Angeles. Stone acknowledged the decisions are difficult and unpopular but said they will eventually become unavoidable.
“I don’t think we can adapt to these climate risks in all areas,” he said. “I think it’s critical to remove populations in a way that leaves them whole. It’s protective of the people we remove, and it’s protective of the people who remain, because then we can use that land for critically needed climate infrastructure.”