What do you suppose will happen when hundreds of millions of people find that their local geography no longer supports human habitation? They will be welcomed into neighboring regions with open arms?
The worst part is, once the killing starts, people will rationalise it to themselves, saying "We didn't have a choice".
I guess I'm in a sarcastic mood today. Yes, of course that will cause mayhem. It's one of the reasons I see climate change as such a threat to our all civilization. We're fearsome tribal creatures and the coming waves of desperate peoples will almost certainly play into the hands of nationalist fearmongers and firebrands.
I wonder if we will see some kind of -literally - ecofashism rise from that.