Even in the shade, a car’s interior can get lethally hot

Don’t count on a shady parking spot to save a child left in the back seat on a hot day.

A new analysis of temperatures inside parked cars reveals that a toddler in a sunbathed vehicle would reach lethal body temperatures faster than one left in the shade. But even in a shaded car, a child could die from overheating within a few hours, researchers report online May 23 in Temperature.

Researchers tracked temps inside three cars — a sedan, economy car and minivan — that were parked in the sun, and another three parked in the shade. Each car started at the outdoor air temperature or 29.4° Celsius, whichever was cooler. On days hotter than 38° C (about 100° Fahrenheit), it took an hour for the average ambient temperature inside the shaded vehicles to reach 38.3° C. For cars in the sun, the inside temperature hit a scorching 46.7° C in an hour, with surfaces such as steering wheels, dashboards and seat covers getting even hotter.

The researchers then simulated how the body temperature of a 2-year-old would increase under those conditions. On average, a toddler’s body would reach the potentially lethal temperature of 40° C (104° F) after about 1.4 hours in the sun and about 2.4 hours in the shade. It happened faster in some cars than others — a child left in a sunbaked sedan could die from overheating in just an hour. 

On average, 37 children in the United States die from heatstroke inside vehicles each year, and in more than half of those cases, the children had simply been forgotten. Car or smartphone alerts reminding drivers to check the back seat could help prevent these deaths, says coauthor Jennifer Vanos, an extreme heat and public health researcher at the University of California, San Diego.