There's a 900 square foot strawbale cabin just a few hundred feet away from me, and I wish I had some actual numbers, but I tell people it's always at least 10 degrees cooler inside in the summer. The walls are literally 18 inches thick. Apparently a "regular" wall has an R value of about 18, and this one is 47! That also means that in the winter it costs just about zilch to keep it warm. If only I could live there....
Sometimes it gets humid here, and that's when the heat makes it sticky, but being a youngster and just getting over it works for me. And I don't even pay the bills! Maybe I'm getting ready for the real life, or maybe I'm just too lazy to even find a box fan.
IIRC, Humans didn't have AC for quite a long time (hundreds of thousands of years?), and survived, obviously. I guess they only lived to 35 if they were lucky though
I prefer the natural methods on just about everything, so if the car gets really hot, I open the windows. FYI, if you open all the doors for just a minute it cools down a lot. I think a lot of people just jump into a car, complain about the heat, and crank the AC. If they would just use some sense and park in the shade or open up the car for a minute, they would benefit from the FE.