Has this summer felt especially hot to you? For at least 41 million city dwellers across the United States, it actually was hotter.

A recent study revealed that more than half of the residents across nine cities are living in zones where temperatures are a minimum of 8 degrees Fahrenheit warmer than surrounding, less developed areas. Researchers found the highest variation in temperatures in Chicago, Miami, New York City, San Francisco, and Seattle. But many other places across the country also experience some level of this heat island effect.

This is part of why the Urban Heat Island mapping campaign was created. The initiative collects hyperlocal heat data to elucidate disparities and vulnerabilities to heat exposure within cities. Now in its seventh year, it’s the country’s largest and most granular effort of its kind. The data, by the way, is gathered by local community scientists. These volunteers include retirees, grad students, and anyone with an interest in advancing equitable solutions to keep the most at-risk residents safe. And they’re already making strides.

First, what counts as an urban heat island?

These are areas with a high concentration of heat-absorbing infrastructure, like buildings, roads, and parking lots. They also tend to have minimal vegetation and be situated far from parks or have little natural shade. As a result, they can get as much as 20 degrees Fahrenheit hotter than nearby greener spots.

What are some of the project’s key findings?

In Raleigh and Durham, North Carolina, volunteers traversed streets by bikes and cars outfitted with heat and humidity sensors, and collected nearly 100,000 data points. Across their study, which was led by the climate-focused data analytics and consulting group CAPA Strategies, they found a 9.6-degree difference between the hottest and coolest areas of Raleigh and a 10.4-degree difference in Durham. Generally, while the results can vary, the root of these significant temperature disparities can be linked back to environmentally racist development policies, which influence where green spaces are placed and where infrastructure like highways and industrial facilities are built. The neighborhoods deemed unworthy of investment, usually low-income communities of color, are now disproportionately suffering from the impacts of climate change as heat waves intensify.

So how does this work impact future planning?

The broader Urban Heat Island mapping campaign has already informed several projects. Raleigh launched a pilot initiative to treat roadways in the hottest neighborhoods with a reflective coating to reduce the amount of heat absorbed. Oklahoma City plans to use the mapping data to reduce minimum parking requirements for developers and cut the amount of pavement needed. (As other cities, like Honolulu, have found, an overabundance of parking lots eats into land that’s better used for things like housing or green spaces.) In Asheville, North Carolina, the data will help with an urban forestry master plan and pinpoint which neighborhoods need more greenery. In short: These are critical changes that will save lives because, in a warming world, every action matters.

Learn more about the Urban Heat Island mapping campaign and how your city can participate.

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The Maui wildfires have the potential to be the worst natural disaster to hit Hawai'i since 1992. Our thoughts are with those who’ve lost loved ones and the residents whose lives have been upended by this catastrophe. Learn more about where the situation stands and how you can help.