[bobthepanda]

There is also humidity. The desert is dry, so you can still perspire and cool down that way; but in a humid place like, say, India it is possible that temperatures will rise high enough that the human body cannot perspire to cool down via evaporation, at which point it would be dangerous to be outside.

[DoingIsLearning]

Indeed "Wet-bulb temperature" is likely to be the thing that will make several densely populated places in Asia uninhabitable.

Bangladesh alone is +170M people. Dispacing these people will be a refugee crisis on an unseen scale.