So Cat, if I understand you correctly, your car is like mine. The back seat folds down so that the trunk space is accessible to the interior of the car? I can put ski poles, skis, and long lumber in the trunk and it pokes right through into the cabin of my car. So air flow would be the same in the trunk area as the rest of the cabin of the car? I would think that a cat in a carrier would STILL be better off in the actual car cabin, oxygen-wise. Next time, you might want to get some cat sedatives from your vet. I'd not recommend trunking your cat again. You really need to be able to make sure the cat is conscious and not suffering from exhaust fumes. The symptoms of exhaust fume asphyxiation is sleeping, by the way. So he might not have been "fine".
Years ago I witnessed our local police canine unit at the local zoo. The officer put the dog in the cruiser with the windows rolled down about 2 inches in the heat of the summer with the car off. After a little while, when he didn't appear to be leaving, I asked him what the hell he was doing with the dog in a hot car. I got a lecture about interfering with the police. I had my young children with me. So I called 9-1-1 and reported a dog locked in a hot car. Another police unit rolled up, and a heated discussion ensued between the officers. The dog was let out and given water. This dog later died from residual damage from the Twin Towers collapse, where he went to search for victims. The handler doesn't lock the dogs in his car anymore, either. And when I see him, I always say "hi".
Supposed animal lovers (like the canine unit) often justify their mistreatment of animals. It's still mistreatment. I look at it this way: You wouldn't lock a baby in the trunk, would you? Then don't put your cat there. And he wasn't "fine", he was sleepy from exhaust fumes.
