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NEW YORK CITY—Driving through New York City’s south Bronx borough on a steamy Saturday in July, Mary Dillon and Kimberly Elicker cringe as another fire hydrant douses the 20-centimeter polyvinyl chloride pipe hanging out their car window.

Fortunately, the cooling spray didn’t prevent the sensor inside the pipe from collecting air temperature and humidity readings as part of a national project to map urban heat islands. The route the two New York City elementary school teachers followed on their 1-hour drive was drawn up with the help of community leaders, who had pinpointed spots where the heat radiating from the pavement and densely packed dwellings feels most oppressive. The input helps Dillon and Elicker, two of the volunteers with the project, map not just heat buildup, but its impact on urban communities.

The approach reflects a growing awareness among climate scientists that environmental equity must be one of their research objectives. “The fact that climate change disproportionately affects communities marginalized along race and class lines is just completely dismissed if these communities are not involved,” says Liv Yoon, a social scientist at Columbia University and lead investigator of the New York City campaign. Scientists, she says, can’t accurately study climate equity without accounting for how people directly experience global warming.

Scientists have known about urban heat islands since the 1880s, when they noted temperatures in London were higher than in surrounding areas. Cities are typically warmer than their suburban and rural counterparts because they lack green spaces, which mitigate the heat radiated by human-built structures made from asphalt, concrete, and brick.

New York is one of 12 cities participating in this year’s mapping campaign, which the National Oceanic and Atmospheric Administration (NOAA) has run for the past four summers in dozens of cities. The teams record morning, afternoon, and evening temperatures on one of the hottest days of the year. The goal is to identify areas with the greatest need for measures—like installing green roofs, operating cooling centers, and planting trees or other vegetation—that are designed to mitigate the effects of the extreme heat.

Hunter Jones, a project manager in NOAA’s climate program office, hopes the mapping campaign raises the profile of a climate phenomenon whose devastating impact is less tangible than wildfires or hurricanes. “We’re doing this project because it makes heat visible,” Jones says. “It catalyzes awareness among individuals and among community leaders of [their] vulnerability and [what] they might be able to do to manage heat in their communities.”

As global temperatures rise and the share of the world’s population living in urban areas is projected to increase from 55% to 70% by 2050, understanding how cities can amplify warming is more important than ever. “If you think about the big challenges of the world, whether it’s energy, water, or food, the cities are where these challenges are being played out,” says Elie Bou-Zeid, an environmental engineer at Princeton University. “When you’re talking about extreme heat, and heat fatalities, even a degree makes a difference. And we know that urban heat islands could [add] several degrees.”

The NOAA mapping effort is being used to design local mitigation efforts. It’s also providing scientists trying to model heat islands with a wealth of additional data. Previous models have been based on satellite data, which record the temperature of the ground itself. But the mapping campaign generates air temperatures close to the ground, which is the heat people actually feel.

One pressing question is how air interacts with buildings of different sizes and compositions, says Dan Li, an atmospheric physicist at Boston University. “There is still a lot of basic physics that we don’t know,” Li says, “and we need to know this to build predictive models.”

The readings Dillon and Elicker collected in the south Bronx will be compared with what other teams gathered 1.5 kilometers away, in Manhattan’s Upper West Side. The tree-lined, residential neighborhood is one of New York City’s wealthiest. It is where Columbia is located, and where Christian Braneon, Yoon’s collaborator and a climate scientist at NASA’s Goddard Institute for Space Studies, is coordinating the teams.

“We really wanted to study two different parts of the city that have very different communities so that we can tease out how the built environment is resulting in different temperatures and different thermal comfort levels outside,” says Braneon, sitting in a lounge chair tucked between two parks. To understand how those differences affect residents, Yoon and Braneon partnered with South Bronx Unite, an organization that advocates for social and environmental justice.

Members of South Bronx Unite helped design the routes through the neighborhood, prioritizing heavily used areas and locations they flagged as particularly warm. Columbia provided funding to pay the participants, which Yoon and Braneon say was key to attracting volunteers to staff each shift.

For Dillard, who teaches science in the South Bronx, mapping urban heat islands is a way to collect information that can be used to make a real difference in the lives of her students. The project also helped her understand their day-to-day experiences.

During a recent field trip, she recalls, “all the kids had their cameras out and they were taking pictures out the window. I asked myself, ‘What am I missing?’ Then I realized, it was just the trees.” The lush green mountains visible from the George Washington Bridge that were part of Dillard’s daily commute were a unique sight for her inner-city students and something they wanted to capture.