Why Car Interiors Get So Hot in Summer

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We've all heard the saying, "If you can't take the heat, get out of the kitchen." But during summer, you could insert the word car into that sentence just as easily.

Why is it that your car feels like an oven, no matter if you park in the sun or shade? Blame the greenhouse effect. 

A Mini Greenhouse Effect

Yes, the same greenhouse effect that traps heat in the atmosphere and keeps our planet at a comfy temperature for us to live is also responsible for baking your car on warm days.

 Your car's windshield not only allows you an unobstructed wide view while on the road, it also allows the sunlight an unobstructed pathway inside your car's interior. Just like , the sun's shortwave radiation passes through a car's windows. These windows are only warmed a little, but the darker colored objects that the sunrays strike (like the dashboard, steering wheel, and seats) are heated immensely due to their lower albedo. These heated objects, in turn, heat the surrounding air by convection and conduction.

According to a 2002 San Jose University study, temperatures in enclosed cars with a basic gray interior rise approximately 19 degrees F in 10 minutes' time; 29 degrees in 20 minutes' time; 34 degrees in half an hour; 43 degrees in 1 hour; and 50-55 degrees over a period of 2-4 hours. 

The following table gives an idea of just how much above the outside air temperature (°F) your car's interior can heat up over certain periods of time.

 

Time Elapsed70 °F75°F80°F85°F90°F95°F100°F
10 minutes899499104109114119
20 minutes99104109114119124129
30 minutes104109114119124129134
40 minutes108113118123128133138
60 minutes111118123128133138143
>1 hour115120125130135140145

As you can see, even on a mild 75 degree day, the inside of your car would warm to triple digit temperatures in just 20 minutes!

  

The table also reveals another eye-opening reality: that two-thirds of the temperature spike happens within the first 20 minutes! This is why drivers are urged not to leave children, the elderly, or pets in a parked car for any amount of time -- no matter how seemingly short -- because contrary to what you'd think, the bulk of the temperature rise happens within those first few minutes. 

More: Keeping Your Pet Safe in the Summer Heat

Why Cracking the Windows is Useless

If you think you can avoid the dangers of a hot car by cracking its windows, think again. According to the same San Jose University study, temperatures inside a car with its windows cracked down rise at a rate of 3.1 °F every 5 minutes, compared to 3.4 °F for closed windows. The  just isn't enough to significantly offset the .  

Sunshades Offer Some Cooling

Sunshades (shades that fit inside the windshield) are actually a better cooling method than cracking windows. They can reduce your car's temperature by as much as 15 degrees. For even more cooling action, spring for the foil type since these actually reflect the sun's heat back through the glass and away from the car.

Why Hot Cars are a Hazard

A stifling hot car isn't only uncomfortable, it's also dangerous to your health.

Just like overexposure to high air temperatures can cause heat illness such as heatstroke and hyperthermia, so can  but even faster since because they. this leads to hyperthermia and possibly death. Young children and infants, the elderly, and pets are most susceptible to heat illness because their bodies are less skilled at regulating temperature. (A child's body temperature warms 3 to 5 times faster than an adult's.)

 

Resources and links:

NWS Heat Vehicle Safety: Children, Pets, and Seniors. 

Heatstroke Deaths of Children in Vehicles. http://www.noheatstroke.org

McLaren, Null, Quinn. Heat Stress from Enclosed Vehicles: Moderate Ambient Temperatures Cause Significant Temperature Rise in Enclosed Vehicles. Pediatrics Vol. 116 No. 1. July 2005.