Ever notice how hot the air gets around parked cars on a sunny day? It’s not just your imagination. Scientists in Lisbon found that parked cars, especially dark ones, really do warm up our cities. A fresh study dives into this finding, showing just how much these vehicles can turn up the heat.
Geographer Márcia Matias, who led the study with her team, confirmed this. They found parked cars, particularly dark ones, can significantly raise street temperatures. Multiply this effect by tens or even hundreds of thousands of cars parked across a city, and you’re looking at warmer air in whole neighborhoods.
You know that feeling when you walk by a parked car on a hot day and feel the heat radiating from it? That’s real! It’s not your imagination.
That’s what Matias, who co-authored the new study, published in the journal City and Environment Interactions, said.
The Air Temperature Difference Around Black and White Cars
Urban areas often become ‘heat islands,’ meaning they’re much hotter than the countryside around them. This happens because of lots of buildings, dark roads, and human activity. This new study points out that parked cars, particularly black ones, are also a major part of this heat puzzle.
To prove their point, Matias and her team ran a simple test in Lisbon. They parked one black car and one white car on asphalt at 8 AM. Both sat under direct sunlight for over five hours. When they checked the surrounding air in the early afternoon, the results were striking:
- The air directly above the black car’s roof was nearly 4 °C hotter than the nearby asphalt.
- The white car, on the other hand, had a much smaller effect. It even made the local air cooler than the street itself.
Physics explains this difference easily. Black paint soaks up most of the sun’s energy, reflecting only a tiny 5% to 10%. White paint, though, bounces back as much as 85% of sunlight. Unlike thick asphalt, cars are made of thin steel or aluminum. This means they heat up super fast and quickly release that warmth into the air around them.
Now imagine thousands of cars parked all over the city, each acting like a small heat source or a thermal shield.
Matias added that “their color can really change how hot the streets feel.”
The Impact of Thousands of Dark Cars Heating the Air Around Them
In a city like Lisbon, researchers counted over 91,000 street parking spots. On a typical weekday, more than 700,000 cars drive through the city. Many of these vehicles end up parked in dense, sunny areas during the hottest hours. By combining field measurements, traffic data, and maps of how land is used, the team expanded their findings to cover the whole city.
What they found was pretty amazing. In parts of Lisbon where parked cars take up 10% or more of the road, switching dark cars to light ones could boost how much sunlight is reflected by up to 19%. That means real cooling could happen. In these specific spots, swapping dark cars for white ones could nearly double the street’s ‘albedo’ – that’s a fancy word for how reflective it is – from 20% to almost 40%. This would drastically cut down on how much solar energy is soaked up and then given off as heat.
Matias points out that city vehicle fleets, taxis, and delivery trucks or vans are “obvious candidates” for switching to lighter colors. Sarah Berk, a climate researcher at the University of North Carolina, agrees. She told the scientific journal New Scientist that using light-colored cars to help cool cities is “particularly innovative.” This is especially true since most city heat plans usually focus on things like roofs and pavements. Cars are different. Unlike thick, slow-to-heat materials like asphalt, their surfaces react very quickly to sunlight.
What’s really interesting is that in Lisbon’s most crowded parts, where roads cover almost a third of the land, cars were seen as the most active factor for heat changes. Buildings were less dynamic. The daily movement of cars from the suburbs to the city center and back subtly shifts the city’s thermal landscape throughout a single day.
How Can Car Colors Help Cool Cities?
While this idea is exciting and offers a fairly cheap way to cut down on urban heat, the researchers also pointed out the study’s limits. Their measurements were taken during peak sunlight on just one summer day. So, the results don’t fully cover seasonal changes, cloudy weather, or the growing number of electric vehicles.
Even with these limits, they suggested several smart strategies for cities:
- Encourage light-colored cars in areas that get very hot.
- Put up shade structures in parking lots.
- Promote reflective coatings for cars.
- Think about rules for parking based on car color in super hot areas.