The Cool Block: Turning Down Urban Heat

View guidelines for use of these broadcast-ready news packages.

Click here for the full media package

BY BEN TRACY, SENIOR CLIMATE CORRESPONDENT ON ASSIGNMENT FOR CLIMATE CENTRAL

Extreme heat is now the deadliest weather-related threat in the United States — killing more people than hurricanes, wildfires, and floods combined. And as climate change continues to drive up global temperatures, summers are only getting hotter. Cities are especially vulnerable due to what’s known as the urban heat island effect, where dense development and a lack of green space can cause some neighborhoods to bake.

Life Inside an Urban Heat Island

In Chelsea, Massachusetts — a small city just across the river from Boston — residents like Arwa Ait Chaib and her mother Wafa are feeling the heat more intensely than ever.

“There are always some days that I feel like we live in the middle of the Sahara desert,” Arwa said.

Summers in Chelsea are far from easy.

“I just can't stand it,” Arwa told us. “It's like, I feel sticky. It's humid out, and if you go out the sun immediately burns your skin.”

Real shade is hard to come by in their neighborhood.

“We had no tree over here at all,” Wafa said.

The Urban Heat Island Effect

Chelsea is a classic urban heat island — a place covered in concrete, pavement, and parked cars that soak up and radiate heat. Research from Climate Central shows that neighborhoods like this can be 15 to 20 degrees hotter than areas with more trees and water.

“So we’re basically an island of hot stuff,” said Bianca Bowman, who works with GreenRoots, a local environmental justice group trying to change that.

The organization has transformed one block in Chelsea into an “urban laboratory” — a community project known as The Cool Block.

“So we looked at those spots and said okay, where can we throw as many solutions as possible to cool those areas down?” Bowman explained.

In this single city block, more than 100 trees have been planted. Streets have been resurfaced in lighter colors to reflect heat. Rooftops are also getting a climate-conscious makeover.

“So when you paint a rooftop white, it’s actually reflecting heat instead of absorbing heat,” Bowman said.

These efforts are more than aesthetic. They could be life-saving. As climate change fuels more frequent and intense heat waves, urban neighborhoods like Chelsea are at serious risk. According to Climate Central, 88% of the 217 U.S. cities it analyzed are experiencing more extremely hot summer days than they did 55 years ago.

Measuring the Heat with Science on the Street

This summer, researchers from Boston University are working with Chelsea residents to study the problem even further. Some families are wearing small sensors to track heat exposure.

“Would you mind putting this on?” one researcher, Madeline, asked a resident.

Small monitors in trees on the Cool Block are collecting data as trees grow and shade begins to take hold to see if air temperatures drop. 

Research shows that parks, trees, and green space can reduce peak urban temperatures by 2 to 9 degrees fahrenheit, but finding space in big crowded cities is not always easy.

Landscape architect Chris Reed has worked on innovative green infrastructure projects throughout Boston and Cambridge — including one that turned a former traffic island into an urban forest.

“It’s one acre of land. It’s a former traffic island. Nothing but gravel was here,” Reed explained.

It now has 400 trees on that one acre. 

 “So you don’t need acres and acres of land,” Reed said. “These kinds of places are in cities everywhere and can be transformed one by one.”

Cooling the Future, One Block at a Time

In Chelsea, that transformation is underway. A paved lot behind the Ait Chaib family’s home is being turned into a park.

“Does it feel like your neighborhood is getting better?” Tracy asked.
“For sure,” said Wafa.
“I can agree on that one,” added Arwa. “We can feel the difference. When you go out you can feel the breeze. You can feel that it’s getting better.”

As cities across the U.S. struggle to adapt to a hotter future, Chelsea’s Cool Block offers a glimpse at what’s possible — one street, one tree, and one rooftop at a time.