That’s the overriding finding from the New York City component of a national project to map urban heat islands. Scientists have long known that urban areas generate heat, but until now they’ve not been able to map them street by street.

The heat trackers told a striking story. On one afternoon in July there was at least a 7-degree difference between the South Bronx, one of the poorest neighborhoods in New York city, and the Upper East Side of Manhattan, one of the wealthiest. The difference was even wider between the South Bronx and Central Park: Nearly 10 degrees.

“We are getting extremely granular data. Street-level data. What right now exists is satellite data where it’s New York City overall. It’s one weather station that covers a vast area, but what we did was we went out and measured temperature along local roads,” said Dr. Liv Yoon, a research scientist at Columbia University’s Earth Institute.

The data can help communities target their financial resources toward reducing temperatures by building more spaces, incorporating lighter colored rooftops, leaving more space between buildings and opening more cooling centers during heat waves.

Melissa Barber, a Bronx native and founder of activist organization South Bronx Unite, has fought for everything from community gardens to redesigning the Bronx waterfront to cool the area around it. Now, working with Yoon, she is using heat mapping to make a case for change to local officials and real estate developers.

 “As community members who actually fight for justice, and social justice, and environmental justice, we can now say, “There is actual data that says, ‘We breathe different air.’ There is actual data that says, ‘We see and feel heat differently than everywhere else,’” said Barber.

“Historically redlined areas certainly they have less infrastructure that is conducive to cooling. They have less green spaces,” said Yoon, who spoke to CNBC one of the very few community gardens in the South Bronx — a garden Barber helped create.

Barber says data will give her more power to change real estate development across poorer parts of New York City.

“We need to really think about how we design communities. When we talk about historical injustice, and we talk about that redlining — there weren’t parks incorporated into that planning. There wasn’t water incorporated into that planning. All of the buffers that actually allow us to experience climate differently did not exist and do not exist for many of our urban communities,” said Barber.

 “It’s really important because heat is one of the most insidious killers in cities. It kills more people than any other natural hazard,” said Vivek Shandas, an advisor with CAPA.

Shandas notes that climate change is upping the ante, increasing heat’s effect on local economies, which now shut down more often due to deadly heat.

“We’re seeing greater intensity of heat. We’re seeing longer durations of those heat waves, and we’re seeing more frequent heat waves come through, yet we’re still using one single number to tell us what the temperature is for a city or a region,” Shandas added.

New York is one of 12 cities participating in this year’s mapping campaign, which is in conjunction with the National Oceanic and Atmospheric Administration.

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