[shalmanese]

Are you asking about humans or civilization? If you look at the habitable range of humans today, obviously a change in a few degrees is not going to do much, some previously habitable land will become uninhabitable and vice versa but large swathes will remain.

Civilization is a lot more fragile and dependant on the pace of change, not the absolute magnitude. The problem with civilization is it's like a Jenga tower, you can continue building higher and higher up the complexity ladder and gradually knocking out supporting pegs for a little bit of time and things will seem fine, but keep knocking out just a few of the wrong pegs and there's no halfway state of falling, it's either intact or severely collapsed.

[cconroy]

Humans, on time scale of 100s of thousands of years. You wouldn't expect Earth to be too dissimilar from today, if not for fossil fuel consumption.