When Cars Become Furnaces
On a hot summer day, walking past a black car often feels like standing next to a furnace. This sensation is not just perception but a measurable phenomenon. Recent research shows that parked dark-colored cars act as miniature heat islands, raising the temperature of city streets by several degrees and worsening the urban heat problem.
The Science of Sunlight and Color
The effect ties directly to how different surfaces interact with sunlight. Dark cars absorb most of the radiation that hits them, reflecting only 5 to 10 percent, while lighter-colored vehicles reflect up to 85 percent. Because thin sheets of metal make up most of a car’s body, they heat up quickly under direct sunlight and radiate that heat outward.
Evidence From Lisbon’s Streets
A study in Lisbon demonstrated this strikingly: a black car parked in full sun increased the air temperature around it by up to 3.8°C more than the surrounding asphalt. Under the same conditions, a white car produced a much smaller heating effect and sometimes even cooled the nearby road surface.
Small Changes, Big Impact
In urban neighborhoods, parked vehicles can cover as much as ten percent of road space, and their warming effect can accumulate. Researchers calculated that replacing dark-colored cars with lighter models could almost double street-level reflectivity and significantly reduce heat absorption. While the study relied on a limited set of measurements taken on a sunny day, the evidence highlights a simple, low-cost strategy to cool cities.
Rethinking Cars in Urban Heat Island Studies
Traditionally, scientists focused discussions of urban heat islands on rooftops, pavements, or tree cover. However, this study reveals that cars themselves contribute to the problem. Beyond their emissions, vehicles physically reshape a city’s thermal environment. Even small changes in car color or parking design could play a meaningful role in creating cooler, more livable urban spaces.
