Hot Enough For You? Cooling The Worsening Urban Heat Island

33:54 minutes

a stylized version of the earth with cloudsThis story is part of Degrees Of Change, a series that explores the problem of climate change and how we as a planet are adapting to it. Tell us how you or your community are responding to climate change here.

The Urban Heat Island

a city skyline under a hazy yellow, brown sunset
Phoenix, Arizona, the hottest city in the U.S. Credit: Shutterstock

We’ve known for more than 200 years that cities are hotter than surrounding rural areas. All that concrete and brick soaks up the sun’s rays, then re-emits them as heat long after night has fallen. On top of that, waste heat from the energy we use to power our buildings, vehicle emissions, and even air conditioning units can cause some cities to be as many as 20 degrees Fahrenheit warmer than their rural surroundings—creating “urban heat islands.” Between the toll that heat takes on the body and the concurrent air quality problems that heat exacerbates, heat waves kill more Americans per year than any other weather-related event. And if enough city residents are using air conditioning to beat the heat, power outages from overworked grids can add to the risk of mortality.

As the globe warms, urban heat islands are projected to become more pronounced, with even hotter temperatures and a more stark urban-rural divide. But scientists and engineers have been working on solutions to reflect the sun before it can raise temperatures, such as cooler roofing materials and heat-reflecting pigments, cool pavements, green roofs, and neighborhood green space. Ronnen Levinson of the Lawrence Berkeley National Laboratory joins Ira to describe what we know about cool infrastructure, while Global Cool Cities Alliance executive director Kurt Shickman explains how cities around the world are implementing solutions—and why it may take something as bureaucratic as building codes to see mass adoption of cooling strategies.

Los Angeles: Cool Roofs And Fitting The Solution To Landscapes

The city of Los Angeles passed the first mandate for residential buildings to have high-reflectivity roofs, a step up from the past requirements, which only applied to flat, commercial roofs. Los Angeles is also pouring cool pavements to test their effectiveness in lowering temperatures.

But how do researchers know these interventions are actually working? And how do you pick the right intervention for any given neighborhood in a city with as big and varied a landscape as Los Angeles? USC scientist George Ban-Weiss talks about his work tailoring cool solutions to individual neighborhoods, and the data that’s still missing as communities weigh the costs and benefits of planting trees versus painting pavement or roofs white.

New York City: Green Roofs And Community Activists

four kids run and play in a large fountain. there is a french architectural arch in the background
Summer in NYC’s Washington Square Park. Credit: Shutterstock

While heat waves are projected to kill thousands of New Yorkers per year by 2080, that pain is not likely to be distributed evenly. Some of New York City’s hottest pockets—near highways and heavy industry, with fewer green spaces—are communities with the most vulnerable populations. And research has found these hotter urban heat islands are home to higher percentages of poor people and people of color. Meanwhile, while New York City alerts residents of heat events and offers cooling shelters for them to go to, the shelters can be difficult for people to access, or even hear about.

But community groups in the Bronx, Harlem, and other parts of the city are working both to cool down their neighborhoods, and connect residents to life-saving cooling. Justine Calma, a reporter for Grist, details the environmental justice problem of the urban heat island, and how New York City is responding.

Phoenix: The Hottest City In The U.S. Is Trying Everything

Phoenix, Arizona, experiences temperatures over 100 degrees in the summer, and researchers are only expecting summers to get hotter and longer. Hot season durations are projected to increase by several weeks on both ends, while the likelihood of temperatures that exceed 115 degrees is only expected to grow. In 2017, an estimated 155 people died of heat-related causes in the Phoenix area.

But the city has been taking the heat seriously. Phoenix has been painting municipal building roofs white since 2006. The city also has ambitious goals to establish shade trees, shelters along public transit routes, and a HeatReady program that would put heat planning on par with disaster preparedness—all with help from scientists like Arizona State University researcher David Hondula. Hondula joins Ira to describe the challenges of getting cities invested in heat preparedness, both short-term and long-term, and what’s next for Phoenix.

How You Are Responding To Urban Heat Islands

How is your county, city, or neighborhood responding to extreme heat? Let us know in the comments below.

Jeremy Hoffman, climate scientist for the Science Museum of Virginia, called in to tell us how his community in Richmond, Virginia developed a method to map urban heat islands. Listen below.

 Transcript: In the summer of 2017, the Science Museum of Virginia hosted a citizen science campaign to measure our city’s temperature during a heat wave. We sent teams of volunteer scientists all over the city with thermometers and GPS units to measure temperatures across various land use types in the city’s metro area. We found a 15 degree Fahrenheit difference between the warmest and coolest place in the same city, on the same day, at the same time. Now, we’re working with the city health department to understand thresholds for issuing heat warnings as we identified higher heat-related illness rates in those warmest zip codes. 

We’re also coordinating with local non-profits to focus tree plantings and greening projects in the most heat-striken areas, which also tends to be areas of extreme poverty and health inequity. We call a team program we developed with a local education non-profit, “Throwing Shade in RVA,” which advances health and climate equity education for local teens. I have many more stories to tell you about heat enrichment, but we’ve since also recreated the same type of study in Washington, D.C. and Baltimore, Maryland, with this summer campaigns happening all over the country.

Citizen science is the best way for us to empower our communities to understand urban heat and then fight back against it. 

Something You Can Do!

a white house with a white roof
Credit: Shutterstock

How can you help your city cool down a bit? Make your roof a cool roof, whether your material is white paint or heat-reflecting shingles. The Cool Roof Rating Council has recommendations for materials you can choose, and a directory of rated products. The CRRC also keeps an updated list of rebates and building codes to help you identify what the requirements for cool roofs are in your city and whether you can save any money on the update.

If you don’t own your home or can’t convince your landlord to make the change, then think on a neighborhood level. Plant a tree (and care for it), or contact your local government about creating green spaces and parks in either your neighborhood, or those that don’t have them. Find out how efforts by South Bronx residents led to the creation of Hunts Point Riverside Park in 2004.

Further Reading

  • Learn about albedo and creating cooler playgrounds with this activity from Science Friday’s education team!
  • Read about how this week major metro areas in the West, including Las Vegas, Phoenix, Sacramento, and San Francisco, were experiencing heat waves with temperatures as high as 120 degrees Fahrenheit in USA Today.
  • Find out more about Phoenix’s HeatReady program for heat readiness in Scientific American.
  • Learn more about the Urban Climate Research Center’s studies at Arizona State University.
  • Learn about Los Angeles’ initiative to pour cooler pavement materials in the Los Angeles Times.
  • Read more on New York City’s bill requiring new buildings to establish green roofs in Dwell.
  • Read Justine Calma’s reporting on how climate action could avert hundreds of heat-related deaths in the U.S. and how heat waves are impacting communities of color in Grist. 

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Segment Guests

Kurt Shickman

Kurt Shickman is executive director of the Global Cool Cities Alliance in Washington, D.C.

George Ban-Weiss

George Ban-Weiss is a professor of civil and environmental engineering at the University of Southern California, in Los Angeles, California.

Ronnen Levinson

Ronnen Levinson is a staff scientist and leader of the Heat Island Group at Lawrence Berkeley National Laboratory in Berkeley, California.

Justine Calma

Justine Calma is a staff writer at Grist. She is based in New York, New York. 

David Hondula

David Hondula is an assistant professor at the School of Geographical Sciences and Urban Planning and is a senior sustainablity scientist at Julie Ann Wrigley Global Institute of Sustainability at Arizona State University. He is based in Phoenix, Arizona.

Meet the Producers and Host

About Christie Taylor

Christie Taylor is an associate producer for Science Friday. Her day involves diligent research, too many phone calls for an introvert, and asking scientists if they have any audio of that narwhal heartbeat.

About Lauren J. Young

Lauren J. Young is Science Friday’s digital producer. When she’s not shelving books as a library assistant, she’s adding to her impressive Pez dispenser collection.

About Ira Flatow

Ira Flatow is the host and executive producer of Science Friday. His green thumb has revived many an office plant at death’s door.

  • Ken

    Any comment about the relationship between cool roofs and solar panels?

  • M Fitzpatrick

    There are some city people who think trees are a nuisance. How can we convince tree haters that trees are good?

  • Brett Nagel

    Just wanted to mention the fact that 20 times more people die from cold than from heat unlike your guests stated.

  • James Golden

    I see that several businesses and hospitals are putting solar panels over their parking lots. This makes the cars a lot cooler, but is that a net good for the city heat island? I’m sure that it’s better than fossil fuel power, but does anyone know if these solar parking lots heat or cool their immediate surroundings?

  • Don Welsh

    Can you explain how the mandates for cool roofs squares with the mandate for solar panels on roofs as I believe all solar panels are dark.

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