Which is the norm and always has been in places like Arizona in the summer. I didn't go out for more than an hour at a time in Tucson in the summer when I lived there. Anything longer and you seriously thought about and prepared for it. This has always been the way humans lived in these areas.
Arizona is a warm, but dry place. Temperature of 38C can be both mildly inconvenient and deadly, depending on the humidity. There are densely populated areas of the world that are much more humid than Arizona and are getting warmer. Eventually people will ditch those places and start to move towards milder climates.
And what do you do if it's not just in the summer, but the whole year? What if it's parts of the earth where a lot of poor people live?
What crops do you grow in those conditions?
So we should be fine with an increasing proportion of the populated environment that never experienced these conditions beginning to?