ARI SHAPIRO, HOST:
In the summer, cities get especially hot. Some of that heat comes directly from the sun, of course, but in urban environments, heat also gets absorbed and then released by the pavement, buildings and other objects.
MARCIA MATIAS: When I'm in the street and I pass by a car, I can feel the heat radiating from it. People often feel this, but they don't ask, why is this happening?
AILSA CHANG, HOST:
That is Marcia Matias, a Ph.D. student and researcher with the Institute of Geography and Spatial Planning at the University of Lisbon. She can cite many reasons why cities are often significantly warmer than surrounding rural areas. The phenomenon even has a name - the urban heat island.
SHAPIRO: And we've known about that for a while, but in her team's new study, published in the journal City and Environment Interactions, Matias writes that one underestimated factor in urban warming is heat radiating from parked cars, especially the darker ones. Matias and her colleagues measured the air temperature in the area around a black car and a white car on a hot day in Lisbon.
MATIAS: The black car would - will be increasing on average the air temperature around it by 2 degrees.
CHANG: Two degrees Celsius - that's about 3 1/2 degrees Fahrenheit.
MATIAS: So it's a very big differences between a dark-colored car and a light-colored car.
CHANG: That's right. The reason for the temperature difference is that white vehicles reflect between 75- and 85% of incoming sunlight. Meanwhile, black vehicles absorb most incoming sunlight, then radiate it out as heat. And Matias says that if you think about this effect with hundreds of thousands of cars, well, all that heat radiating back into the city adds up.
MATIAS: We are making plans about climate change based on models that don't account for specific elements. Probably we should be also thinking about how cars are influencing our air temperature inside cities.
SHAPIRO: The study does note that this data was gathered at one specific time, but Matias is confident that vehicle colors do impact air temperature.
CHANG: In addition to other urban heat mitigation strategies, like more green spaces, more trees and more shade, Matias says governments could encourage manufacturers to use reflective coatings or get people to simply buy brighter cars.
SHAPIRO: She says fleets of municipal vehicles, like buses and police cars, would be a good start and could be a small step in making the sweltering summer heat a little more bearable.
(SOUNDBITE OF NELLY SONG, "HOT IN HERRE") Transcript provided by NPR, Copyright NPR.
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