The atmosphere and the windows of a car are relatively transparent to the suns shortwave radiation (yellow in figure below) and are warmed little. This shortwave energy, however, does heat objects it strikes. For example, a dark dashboard or seat can easily reach temperatures in the range of 180 to more than 200 degrees F.
These objects (e.g., dashboard, steering wheel, childseat) heat the adjacent air by conduction and convection and also give off longwave radiation (red) which is very efficient at warming the air trapped inside a vehicle.
(Animation Courtesy of General Motors and Golden Gate Weather Services. Use of this animation does not imply NWS endorsement of services provided by General Motors and Golden Gate Weather Services)
Never Leave Children or Pets In Unattended Vehicles
Each year dozens of children and pets die from being left in unattended vehicles across the country. Catherine McLaren MD et al published an article in Pediatrics in 2005 titled "Heat Stress From Enclosed Vehicles: Moderate Ambient Temperatures Cause Significant Temperature Rise in Enclosed Vehicles." which showed evidence that at relatively cool outside temperatures, the temperature inside a vehicle can rise significantly, with the majority of the temperature rise occurring within the first 15 to 30 minutes. In addition, they found that leaving windows cracked does not significantly slow the heating process or decrease the maximum temperature measured inside the vehicle. To prevent serious heat related illness or death, children should never be left unattended in a vehicle.
The temperature inside a vehicle will reach 100F in 25 minutes when the outside temperature is only 73F!
Temperature inside a vehicle (air temperature ranging from 73 - 93 F)
Temperature inside a vehicle (closed vs cracked window)
Excessive Heat Safety
* Drink plenty of water and natural fruit juices, even if you're not thirsty. Avoid alcoholic beverages and drinks with caffeine, such as coffee, tea, and colas.
* Wear loose-fitting, lightweight, light-colored clothing. If you must go out, use sunscreen and wear a wide-brimmed hat. Remember that sunburn reduces the skin's ability to provide cooling.
* Avoid going out during the hottest times of the day. Take frequent breaks if working during the heat of the day.
* Using a buddy system between co-workers in high heat-stress jobs can help ensure that signs of heat stress do not go unnoticed.
* Inside during the day, keep shades drawn and blinds closed. Use air conditioning whenever available. Even just two hours per day in air conditioning can significantly reduce the risk of heat-related illness.
* Fans should only be used in a ventilated room. Blow hot air out a window with a fan during the day, and blow in cooler air at night.
* Take cool (not icy cold) baths or showers. Eat frequent, small meals. Avoid high protein foods, which increase metabolic heat. Fruits, vegetables, and salads constitute low protein meals.
* Do not leave children or pets in a closed vehicle with the windows up. Temperatures inside a closed vehicle can reach over 140 degrees within minutes.
* Provide extra water and access to a cool environment for pets.
* Listen to NOAA Weather Radio or media sources to keep up with the latest heat watches, warnings, and advisories.
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