On a hot day, the inside of a car can become lethally hot, reaching 125°F (52°C) or higher within an hour, even when the outside temperature is only in the 80s°F. This rapid heating occurs due to the greenhouse effect, where solar energy enters through the windows and is trapped inside, heating the interior surfaces and air. This is not just uncomfortable; it's a critical safety hazard, especially for children and pets.
The temperature rise is most dramatic within the first 10-20 minutes. Cracking a window open does little to slow this process. The dashboard, steering wheel, and seats can reach temperatures high enough to cause burns. For parents and pet owners, this is the most crucial point: there is no safe amount of time to leave a living thing in a parked car on a warm day.
The following data illustrates how quickly a car's interior temperature can climb on a sunny, 85°F (29°C) day. These figures are based on studies from organizations like the National Highway Traffic Safety Administration (NHTSA).
| Time Elapsed | Approximate Interior Temperature | Notes / Comparison |
|---|
| 0 minutes | 85°F (29°C) | Starting ambient temperature. |
| 10 minutes | 105°F (41°C) | A 20°F (11°C) increase in just 10 minutes. |
| 20 minutes | 115°F (46°C) | Hot enough to cause discomfort and dehydration. |
| 30 minutes | 120°F (49°C) | Body's internal cooling mechanisms begin to fail. |
| 60 minutes | 135°F (57°C) | Extreme danger zone; risk of heatstroke is severe. |
The color of your car's interior and exterior also plays a role. A black interior can be 20-30°F hotter than a light-colored one. To prevent this, always park in the shade, use a sunshade for your windshield, and consider window tinting that blocks infrared radiation. The most important takeaway is to never leave children or pets unattended in a vehicle, regardless of how short you think the errand will be.
