First off, you're exaggerating. There is no place on earth that averages 40C for 3 months.

Second,I live in Tokyo, where the summer has been miserable with average temperatures of 32C, with regular highs of 36+ with 80% humidity. And yet I walked and biked everywhere and was just fine, and that's true for most of the 40M people that live here as well.

Third, it sounds like you live in a place that's not suitable for humans, you should probably move instead of making the planet even hotter for everyone else by living in your steel boxes with AC.