I'm just making assumptions here, but if an average increases by 2 degrees, that could mean that the outlier maximum temperature can reach 4-5 degrees. For areas where this temperature is already in the 45-50(Celsius), that's probably uninhabitable (at least for poor people).

This will probably mean that there will be a wave of ecological emigration moving towards the more temperate areas of the globe.

So, it's not an uninhabitable earth unless you are poor and live around the dry tropical/ecuatorial areas. And there are a lot of people there.