Sufficiently high CO2 levels, such as existed at the end of the Permian period, can raise temperatures above that which would be survivable. Sure, people could huddle in air conditioned survival pods. This doesn't seem to be a sufficient rebuttal of the claim.
If you think an analogy with the P/T extinction is invalid, note that CO2 levels are rising now much faster than they did over that event.
> people could huddle in air conditioned survival pods. This doesn't seem to be a sufficient rebuttal of the claim
I kind of think it does, particularly when we’re talking about temperatures that humans choose to live in (almost precisely as you describe) today.
CO2 is not going to render our inland cities uninhabitable. It will make them more deadly, more expensive and less comfortable. It will cause a continuation of the current extinction event, which is already comparable with (if not equivalent to) P/T.
This is hyperbolic. It will make it more expensive. But not uninhabitable.
You know what would render sections of it literally uninhabitable? A Union Carbide incident [1].
[1] https://en.m.wikipedia.org/wiki/Bhopal_disaster