It’s about to get hotter in our nation’s cities. Just how hot it gets depends not only on the weather, but also on infrastructure, working conditions and ZIP codes.

When that heat bears down on cities, with all their steel-and-concrete infrastructure, it can create what scientists call an “urban heat island.”

Under this phenomenon, concrete structures and roads can essentially act like “heat batteries,” where man-made surfaces absorb and emit more heat than natural landscapes, like grass or trees, leading to elevated temperatures, said Luis Ortiz, an assistant professor in the department of atmospheric, oceanic and earth sciences at George Mason University, and a member of the New York City Panel on Climate Change, an advisory body that helps inform policy on climate issues.

Other factors contribute too—machinery like air conditioners eject heat into the atmosphere, and tall buildings block cool gusts of wind.

Temperatures can vary across big cities like New York and Houston, depending on the landscape and the amount of green space and trees in a given neighborhood. Local scientists and community organizations have worked to understand the urban heat island effect over the past few decades. But the average city resident doesn’t always know that their neighborhood may feel hotter than the temperature from weather forecasts.

Scorching Cities

Around 150 Houston residents attached temperature sensors to the windows of their cars and drove around the city in 2024 to document the urban heat island effect in real time. This was the second study of its kind for the Houston Advanced Research Center; the first happened in 2020.

As expected, the results showed that areas with denser development and less tree cover were hotter. For many volunteers, it offered a snapshot of a problem that they can feel the effects of, but may not always be able to prove. It was not just about the science, said Meredith Jennings, the director of local government and community initiatives at the Houston Advanced Research Center, who worked on both experiments.

“For people to participate in this campaign and talk about it on the news and see how heat impacts people differently,” she said. “That can inform how people take action.”

From 2016 to 2024, the National Oceanic and Atmospheric Administration, in partnership with other federal agencies, funded the mapping of the urban heat island effect in American cities, including Houston. The U.S. Department of Agriculture funded the second study through a program to increase tree canopy in underserved communities. With recent federal cutbacks on climate research, the future of mapping heat and cooling in cities may now rest more firmly on the shoulders of local leaders.

In many cities across the country, you are more likely to live in a hotter neighborhood if you are low income or a person of color.

Communities in neighborhoods with very little green space have also often suffered because of their proximity to industry, such as power plants—which release heat while operating—and highways. A recent study found that highway expansions can considerably worsen the heat island effect.

In hotter neighborhoods, air conditioners are often used more frequently. Research has linked buildings’ higher cooling energy demand to urban overheating—and that’s if the resident even owns an air conditioner and can afford to use it amid rising electricity costs.

According to New York City data, Black New Yorkers are twice as likely to die from heatstroke, with death rates twice that of white residents. They are also less likely to operate an air conditioner. The city’s panel on climate change has predicted that the number of hot days and nights will increase between 15 and 52 days by midcentury.

Overheating and heat-exposure illnesses, such as sunstroke, can be very taxing on the human body, Ortiz said. Informing the public, especially outdoor workers, about heat-related health risks is crucial, he said. My colleagues Keerti Gopal and Martha Psowski have written about the threat that heat exposure poses to Texas construction workers.

But that’s not to say that cities are always more dangerous than rural areas during periods of extreme heat. Ortiz pointed out that in New York, for example, the dense buildout means that help in the form of cooling centers—air-conditioned rooms that local officials open up to the vulnerable public on very hot days—or even just a cool store or library, can be more readily available than in a suburban or rural environment.

Cooling Down

Climate change is making our summers warmer, and this summer seems poised to continue that trend.

City governments that want to cool down hot neighborhoods can take practical steps like adding green spaces and street trees as well as using roof and pavement materials designed to absorb less heat.

Although planting trees is a proven way to cool neighborhoods by providing shade and lowering air temperatures, maintaining street trees can be costly, especially when they are dying from drought.

In New York, the city’s forthcoming Urban Forest Plan will be designed to cover 30 percent of the city with tree canopy, in part to reduce heat in certain areas. I reported in December that the city received state funding to plant and care for trees in its ailing forests. But the underfunded Parks and Recreation Department may struggle to keep up.

Since 2020, Houston leadership has been tracking tree plantings across the city, in line with a city plan that sets out a framework to achieve carbon neutrality by 2050, and greater resilience to climate change. According to the plan, city residents are forecast to experience 74 days a year with a heat index—a measure that assesses how a mix of heat and humidity feels to the human body—of 105 or more by 2050. Currently, they experience an average of only 10.

“Climate projections and the historical trends—they’re all pointing toward summers becoming more and more unbearable and longer,” Jennings said. “So this really becomes a quality of life issue.”

More Top Climate News

Wildfires have destroyed grasslands across Nebraska, culminating in the loss of over a million acres, reports Gabrielle Canon for The Guardian. A warmer, drier winter created the ideal conditions for the fires, one of which was the largest blaze ever recorded in the state. My colleague Jake Bolster recently wrote about how this weather has led to fears of large wildfires in neighboring Wyoming.

Environmental Protection Agency Administrator Lee Zeldin has radically shifted the agency’s mission, according to a recent New York Times analysis of EPA officials’ public communications by Lisa Friedman and Harry Stevens. As the leader of the EPA, Zeldin often discussed the need to cut red tape for businesses, and rarely mentioned environmental harms to children, according to the analysis.

U.S. Sen. Sheldon Whitehouse (D-R.I.), the ranking member of the Senate Committee on Environment and Public Works, sent a letter to the CEO of French company TotalEnergies questioning the legality of a nearly $1 billion settlement with the Trump Administration to relinquish its offshore wind leases, Kelsey Tamborrino reports for Politico’s E&E News.