A car parked in 60-degree Fahrenheit (approximately 15.5°C) weather can become dangerously hot, reaching over 100°F (38°C) in as little as 10 minutes and potentially exceeding 130°F (54°C) within an hour. This rapid temperature rise is due to the greenhouse effect, where solar radiation enters through the windows and is trapped as heat inside the vehicle. This is a critical safety concern, especially for children, pets, and even items left inside.
The exact interior temperature depends on several factors. Direct sunlight is the most significant variable; a car in the sun will heat up much faster and to a higher peak temperature than one in the shade. The color of the car's exterior also plays a role, with darker colors absorbing more heat. The length of time the vehicle is stationary is, of course, a direct factor.
It's a common misconception that slightly cool weather is safe. The internal temperature of a car is not dependent on the outside temperature being extremely high. The sun's energy is the primary driver. To illustrate how quickly conditions can change, here is a typical temperature rise for a sedan in direct sunlight on a 60°F day:
| Time Elapsed | Approximate Interior Temperature |
|---|
| 0 minutes | 60°F (15.5°C) |
| 10 minutes | 100°F (38°C) |
| 20 minutes | 115°F (46°C) |
| 30 minutes | 120°F (49°C) |
| 60 minutes | 130°F (54°C) |
To mitigate this, always try to park in a garage or in the shade. Using a windshield sun shade can significantly reduce the initial heat buildup. If you must leave an item or a person in the car, even for a "quick" errand, it is never safe. Cracking the windows open has a minimal effect on slowing the heating process and does not prevent the interior from reaching dangerous levels. The only safe choice is to never leave a child or pet unattended in a vehicle, regardless of the weather.
