Each year, a few dozen children die of heat stroke after having been left unattended in vehicles. These easily preventable tragedies happen through out the summer, not just on scorching hot days. Researchers in California measured how much cars heat up as well as whether leaving the windows cracked keeps it cooler inside.

What the researchers wanted to know: How quickly do parked cars heat up in the summer?

What they did: The authors conducted their research on 16 sunny California days, with temperatures between 72 and 96 degrees Fahrenheit. They parked a dark sedan at an angle such that direct sunlight did not pass through the windshield. The car's initial interior temperature was the same as the outside temperature. Then, with the windows closed, researchers measured the interior temperature of the car every five minutes, for a total of an hour. On two of these days, they also took the temperature inside the car for an hour with the windows cracked.

What they found: Researchers found that the car's interior temperature rose at essentially the same rate, an average of about 3 degrees every five minutes, regardless of whether the outside temperature was 72 or 96 degrees. After an hour, the final temperatures recorded averaged about 40 degrees higher than the initial temperatures, with all final temperatures topping 110 degrees. Moreover, about 80 percent of this heating up happened in the first half an hour. Cracking the windows open did not significantly affect either the rate at which the temperatures rose or the final temperatures recorded.

What it means to you: Even if you think it's a relatively cool summer day, leaving a child in an unattended car could be dangerous. Kids are particularly susceptible to heat illness because they do not regulate their core body temperature as well as adults do, and they often cannot shed layers or grab a cold drink when feeling hot. If you suspect that your child has heat illness, with symptoms such as an elevated temperature, headache, thirst, nausea, and irritability, seek medical attention right away.

Caveats: This study only recorded a car's interior temperatures. It is still unclear how much heat exposure is safe for children as such research would be unethical to conduct.

Find out more: The National Institutes of Health has a page with links to different sites that have information on heat illness.

The website KidsHealth.org has a fact sheet on heat illness in children.

Read the article: McLaren, C., et al. "Heat Stress from Enclosed Vehicles: Moderate Ambient Temperatures Cause Significant Temperature Rise in Enclosed Vehicles." Pediatrics. July 1, 2005, Vol. 116, No. 1, pp. e109-e112.

Abstract online: http://pediatrics.aappublications.org