Editor’s note: This story corrects the location of the temperature measuring device on a car. We regret the error.

(WKBN) – It is not a secret that September has been off to a hot start in the Valley. Just Tuesday, the high temperature at the Youngstown/Warren Regional Airport reached 90°F for the second time in 2023. The heat and humidity probably have your car air conditioner on high once you get inside.

While the high temperatures this week have been around 90°F, you might have noticed that your car reports temperatures that are much higher. What is the reason for this difference?

Well, the light that passes through your car window has substantial energy, which means it has a high wavelength. The sunlight heats up the interior of the car, but the heat that radiates off of the leather, seats, and plastic is not as energetic, which causes it to be trapped inside the car.

This results in a “greenhouse effect” that heats the car to temperatures much higher than the outside temperature.

Here is an example of the temperature inside a car after 60 minutes of exposure with an air temperature of 80°F:

Example of the temperature inside a car after 60 minutes of exposure with an air temperature of 80°F (Courtesy of the National Weather Service).

Not only does this have an effect on the temperature in the interior of the car, this affects the temperature under the hood as well.

The temperature reported by a car is not actually measured by a thermometer but a thermistor. Thermistors measure the change in electrical resistance when heat is added or taken away. Now, the problem is not that temperature is measured by a thermistor but the issue is where the thermistor is located.

Typically, the thermistor for cars is located in the front of a car behind the grill. Therefore, the heat that builds up under the hood of the car creates a hot bias on the temperature reading. Additionally, this reading is affected by the heat that is absorbed by the pavement that radiates upward, under the hood of the car.

The result is a temperature reading that is several degrees above the ambient temperature outside.

How hot does it get inside of cars?

The temperature inside the interior of cars can be substantially higher than the outside temperature.

Even if the air temperature is in the 70s, the temperature in a car can rise over 110°F after 60 minutes time. Temperatures in the 90s can result in a temperature inside the car of over 130°F!

The temperature of a vehicle between 0 and 60 minutes as a function of air temperature (Courtesy of the National Weather Service).

There are many who crack the windows of their cars to try and mitigate this issue. While this does help slow the heating of the vehicle, eventually the difference in temperature between a car with and without cracked windows becomes minute.

The difference in the temperature of a car with cracked windows and a car with closed windows (Courtesy of the National Weather Service).

The heat that builds up inside cars is why you should never leave pets or children inside a vehicle with the windows closed or without the air conditioner turned out. Heat is responsible for the largest number of fatalities related to any other weather event. Therefore, it is important to keep safety in mind during these hot and humid conditions.