During Arizona's population boom in the 1990s (about 1.5 million new inhabitants) a morning drive-time radio host in Phoenix told his listening public that if they were parking their car outside (temps were heading to 100 plus), put a package of microwavable popcorn on the dashboard.

On the way home from work they'd have freshly popped corn.

That's how hot it can get in a parked car — and why every year so far in the 21st century between 30 and 60 U.S. children have died from the heat after being left unattended in a parked car.

Those upsetting stats prompted researchers to do a study that "not only quantifies temperature differences inside vehicles parked in the sun ... but it also makes clear that even parking a vehicle in the shade can be lethal to a small child."

They found that in Tempe, Arizona (a Phoenix suburb), when daytime temperatures went to 95 degrees, after one hour — their estimated time for a shopping trip — temperatures inside a car reached 115 F, seats were 124 F, steering wheels 127 F and dashboards 156 F.

Even in vehicles parked in the shade, cabin temps were above 100 F. The researchers said a child (depending on height and weight) generally will suffer heatstroke when core body temperature reaches 104 F, so there's no time that's safe to leave little ones in the car.

As inconvenient as it may be to unpack them for a short run into a store, just do it — or use the phone or Internet for home deliveries.