And yes climate change is a constant in history. However what is new is significant change in the timescale of a human life. Meaning we won't adapt gratefully as a society. Previously cities becoming uninhabitable would be abandoned slowly over the course of centuries.

Now we will have a situation where a significant portion of the population will have to move in their lifetime. That's the kind of stuff that causes hostility and wars. And given how good we've become at mass-killing humans, that is a frightening prospect.