> recent refugee crisis
This and that are very different things.
A refugee crisis involves people from country A becoming forcefully intermingled with people from country B: moving into their cities, sharing their resources, voting in their elections, etc.
What I’m talking about here, is effectively a series of land purchases made by every country from its bordering neighbours — like the Louisiana Purchase, or the Gadsden Purchase. But where the assumption is that only the land is acquired — while the people residing on the land before the purchase, are expected to have resettled (and been provided assistance to resettle by their own government) so that by the time of the purchase, the land is uninhabited, free for resettlement by the acquirer.
These people aren’t “resettling in northern countries” — the northern country is now just north-er than it was before. The people affected would be resettling in newly-developed cities within newly-purchased territory of their own country, to get away territory that was of their own country but has now been lost/sold.
(For much of human history, people were very used to packing up and moving away from contested borders. We’re actually rather good at it, as a species.)
Or, nearest the equator, people would be moving to get away from territory that just can’t be lived in by anyone, anymore. Such territory would be declared unlivable by global treaty, and the people there would thus be considered refugees of whatever country claims the area, similar to disaster victims. Countries whose whole territory became unlivable would indeed become stateless refugees, in need of an offer of refugee citizenship by some other country. But there’s rather few of those, as most people give up on non-arable land long before it becomes that bad. (See: the thing most https://en.wikipedia.org/wiki/Terra_nullius regions have in common.)
To be clear, that last bit is not a political argument. That’s a fact. Those people are climactic refugees — disaster victims. They already have a refugee’s need to live somewhere. We’re just currently ignoring their plight, because it’s only affecting these few people who have so little. That could change, if the same problems begin to affect large swathes of the world.
> most people don’t actually want to leave their homes ... it would be a lot be there to not have a need for mass migrations in the first place
I mean, obviously. I just think it wouldn’t be all that bad a thing for humanity as a whole if it did happen; not that anyone would choose to do it.
If every human were chased around by their own personal (de-fanged, de-clawed) tiger for an hour every day, we’d all be in much better shape. That doesn’t mean anyone would sign up for it. It’d be better to not have the tigers, obviously! It just means it’s not necessarily a disaster for humanity if that comes to pass.