On a blazing summer day, stepping into a parked car can feel unbearable. But scientists in Lisbon warn that the problem doesn’t stop inside the car, it spreads to entire neighbourhoods.

Researchers compared a black and a white car left outdoors in 36°C heat. The black car raised nearby air temperatures by almost 4°C, while the white car had a much smaller effect. The reason is simple: white paint reflects most sunlight, while black absorbs it, turning cars into heat radiators.

This matters because of the urban heat island effect, where cities trap more heat than surrounding areas due to concrete, asphalt, and human activity. At night, city temperatures can stay up to 10°C higher, worsening health risks like dehydration, heat stress, and even death.

Experts say something as simple as lighter paint jobs could help. Repainting fleets of taxis, buses, or delivery vans could boost reflectivity on streets and reduce local temperatures.

Cities across Europe are already greening streets and creating climate shelters, but this new research suggests your car’s colour could also be part of the solution.