When it gets really, really hot outside, like well over triple digits, it's not uncommon for somebody, probably from the local news station, to crack an egg on the sidewalk to see if it'll fry.
It takes a little more effort to bake cookies. But apparently, it can get hot enough to do that too. What this requires is temperatures getting up into 120, high 110's, being in Phoenix, and leaving some cookie dough in a car with the windows up. (Also aluminum foil.) The National Weather Service, who attempted this, didn't have a thermometer on hand, so the exact temperature isn't available, but they do know that temperatures inside the car topped 200 at least. As a control, cookies were also put on the sidewalk.
After four hours, they had fully-baked cookies (and a car that smelled like cookies). The, um, chef, Charlotte Dewey, says she probably could have taken them out of the car after two hours, but she wanted to make sure the cookies were done on the inside as well. The sidewalk cookies didn't quite work out.
That's a hint. If the car's hot enough to bake cookies, imagine what it can do to you. Roll the damn windows down. Or use the air conditioner. Or reconsider if you really need to drive.