With the arrival of warmer temperatures and sunny days, drivers are often reminded to be more vigilant about checking the back of their vehicle after parking it. If a child or pet is inadvertently left behind, they can quickly be exposed to lethal temperatures as the vehicle's interior heats up.

A new study by researchers at Arizona State University and the University of California San Diego School of Medicine suggests that the air temperature in a parked vehicle can reach dangerous levels within one hour. Even when parked in the shade, warm outside temperatures can put a child at risk of heatstroke within two hours.

The study, which was published in the journal "Temperature," parked vehicles in different amounts of sunlight and shade on three summer days where the temperature exceeded 95 degrees Fahrenheit. The study was conducted in Tempe, Ariz., and also simulated how the vehicle temperature would affect a two-year-old child left inside.

Six vehicles, all silver, were used in the study. These included two midsize saloon cars, two city cars, and two minivans. The vehicles were moved from direct sunlight to shade for varying lengths of time over the course of the day.

"These tests replicated what might happen during a shopping trip," said Nancy Selover, an Arizona State climatologist and co-author of the report. "We wanted to know what the interior of each vehicle would be like after one hour, about the amount of time it takes to get groceries. I knew the temperatures would be hot, but I was surprised by the surface temperatures."

Researchers monitored the temperature within the vehicle as well as the surface temperature of various cabin features. Vehicles parked in direct sunlight had an average cabin temperature of 116 degrees after an hour. The average seat temperature measured 123 degrees, while the steering wheel heated up to 127 degrees. Dashboards had the hottest surface temperature, averaging 157 degrees after an hour.

Even when parked in the shade, a vehicle's interior heated up considerably. The average cabin temperature after an hour in the shade was 100 degrees. The seats had an average temperature of 105 degrees, the steering wheel temperature hit 107 degrees, and the dashboard temperature reached 118 degrees.

"We've all gone back to our cars on hot days and have been barely able to touch the steering wheel," said Selover. "But, imagine what that would be like to a child trapped in a car seat. And once you introduce a person into these hot cars, they are exhaling humidity into the air. When there is more humidity in the air, a person can't cool down by sweating because sweat won't evaporate as quickly."

The study noted how a person's age, weight, existing health problems, and other factors will influence how susceptible they are to heatstroke. However, children are generally considered to be most at risk when their core body temperature exceeds 104 degrees for an extended period of time. Jennifer Vanos, co-author of the study and an assistant professor at UC San Diego, said children could also suffer permanent neurological damage from prolonged exposure to sweltering temperatures.

"Internal injuries can begin at temperatures below 104 degrees," said Vanos. "As compared to adults, children have a quicker rise in core temperature and a lower efficiency at cooling."

The study used data to model what a hypothetical two-year-old child's body temperature would be over the course of the study period. Researchers found that temperatures could reach lethal levels for a child after an hour of a vehicle being parked in the sun and after two hours of a vehicle being parked in the shade.

The type of vehicle had some effect on how quickly a vehicle heated up. The temperature in the city cars went up faster than both the midsize saloon car and minivan temperatures.

"We hope these findings can be leveraged for the awareness and prevention of pediatric vehicular heatstroke and the creation and adoption of in-vehicle technology to alert parents of forgotten children," said Vanos.

Several automakers have started to add back seat alert systems to help prevent drivers from leaving children, pets, or items in their vehicle. These systems typically note when a rear door has been opened before a trip and will honk the horn, flash the lights, or otherwise warn the driver if they do not open a rear door shortly after turning off the vehicle.

The National Highway Traffic Safety Administration says heatstroke deaths frequently happen when a parent accidentally forgets that their child is in the vehicle. This is more likely to happen if a regular routine has been altered, such as an adjustment in who takes a child to daycare. Making a quick call to your spouse or a person at the child's destination can ensure that they arrived safely.

Getting into the routine of checking the back seat after every trip can also help ensure that nothing is left behind. Keeping your phone, briefcase, or another important item in the back of the vehicle can help you get into this habit.

Heatstroke deaths can also occur if an unattended child gains access to a vehicle. Keep your keys out of reach of young children to prevent this type of incident.