My Dog is Cool | How Hot Do Cars Get?
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How Hot Do Cars Get?

Have you ever noticed how hot it can get inside a car on a summer day — far hotter than it is outside! That’s because a car acts like a greenhouse (called the “Greenhouse Effect”) trapping the sun’s heat.

Check out this animated video of the Greenhouse Effect in action on a hot car, by the cool people at Golden Gate Weather Services.

The below study by the Animal Protection Institute showed that hot temperatures outside can quickly lead to deadly hot temperatures inside a closed car. This study was conducted during a local heat wave in Sacramento CA. However, notice on day three, the temperature starts out at a reasonable 72 degrees.

This study compared an outside temperature of a shaded area with the inside of an automobile in three states: fully closed, with four windows cracked, and with two windows cracked. Inside temperatures were measured with an indoor/outdoor thermometer and an oven thermometer (both readings are given). All temperatures use the Fahrenheit scale.

Day 1
Outside “Shaded” Temperature
Inside Closed Automobile
Indoor/OutdoorOven Thermometer
9:00 am82°109°---
9:30 am87°115°---
10:00 am91°115°---
10:30 am94°114°115°
11:00 am98°114°119°
11:30 am100°117°124°
12:00 pm101°119°127°
1:30 pm112°124°130°
2:30 pm125°130+°159°
4:00 pm98°110°110°
Day 2
Outside “Shaded” Temperature
Inside Closed Automobile
Indoor/OutdoorOven Thermometer
9:15 am84°98°98°
10:00 am88°103°105°
10:30 am90°108°108°
11:00 am92°109°109°
12:00 pm95°113°113°
1:00 pm101°114°115°
2:00 pm110°123°120°
3:40 pm112°129°128°
4:00 pm115°132°130°
Day 3
Outside “Shaded” Temperature
Inside Closed Automobile
Indoor/OutdoorOven Thermometer
8:30 am72°72°72°
9:30 am80°95°95°
12:00 pm88°105°105°
1:50 pm99°109°109°
2:30 pm104°120°120°

Other studies show similar results:

  • San Francisco State University – April 2007 fact sheet utilizing data from a Golden Gate Weather Services study
  • Another study reprinted from the Journal of the Louisiana State Medical Society
  • A study from Stanford University shows that even on comparatively cool days, such as 72 degrees, a car’s internal temperature will rocket to 116 degrees within 60 minutes. And keeping the windows open a crack hardly slows the rise at all.