My dog is a bc. He rides with me everywhere but he loves the winter for some reason. That whole back end of my SUV is like a giant play room for him. All toys, some bones, and a small comforter. I am always concerened that one day a person is going to see my Buddy and smash the windows in the car in summer when the air is on. Or winter when a little bit of heat is on. And yes I will say it i am a big pushover for animals.
The amount of energy from sunlight it takes to warm a car up to a dangerous levels is far lower then for a house.