Because there is no agreement needed - those who can do might just do.

So, it's war, then?

I don't see why it would be. Just as it is not war now with respect to pollution and might also not be in the future. Before it is being cited: of course, the defense establishment sees risks of war everywhere, including climate - but that is their business.

There are already existing tensions and conflicts about resources like water. Some of these do not need much more pushing to escalate into war[0].

Further climatic disruptions will make the already dire situations in many countries untenable. That situations like that do not tend to improve by unilateral actions of their neighbors if the threaten to make a barely acceptable situation even worse.

https://www.thetimes.co.uk/article/the-first-water-war-is-un...

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?

Unfortunately, killing hundreds of millions of starving people can be done very easily -- much more easily than solving the underlying problem. The areas that become uninhabitable will then not be able to produce more starving people, so such an atrocity need only be carried out once.

The worst part is, once the killing starts, people will rationalise it to themselves, saying "We didn't have a choice".

Of course they will be. That's just what happened during the Syrian civil war; the refugees were welcomed with open arms in Europe, Germany didn't experience any political turmoil that reverberates to this day at all.

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.