There is absolutely no way I can think of in which this could be done diplomatically. In the recent refugee crisis [1] a few million people moving in almost caused the EU to collapse.
It's mindbogglingly naive to imagine that hundreds of millions of people from the most affected areas will just be able to resettle in Northern countries.
Aside from this, I suspect that most people don't actually want to leave their homes unless they really have to. It would be a lot better to not have a need for mass migrations in the first place, rather than cross our fingers and hope for the best.
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.
> a series of land purchases made by every country from its bordering neighbours
Which nation state would allow for this to happen? The US, which is now trying to build a wall along its Southern border? The Europeans who almost cancelled the Schengen agreement over the wave of refugees? Australia that houses refugees on an island prison[1]?
Nobody would sell their land to foreigners. No nation state would give up resources out of humanitarian concern.
> The people affected would be resettling in newly-developed cities within newly-purchased territory of their own country
Who would even pay for this? We're talking about tens of trillions of dollars.
[1] https://en.wikipedia.org/wiki/Australian_immigration_detenti...
Since you have not provided any discussion on the enormous obvious objections, this is effectively a troll (can I use that word?).
It's a comment bomb that would require dissenters to argue with specificities which you have declined to include, in some grossly asymmetric waste of time and energy.
So I leave this response, in lieu of a downvote.
But I did bring it up, because I find myself wondering lately about the objections to those objections. Assume the objections; then try to work out a world where this happens anyway. Do we live in a world that’s anything like that world? What would have to be true, for this to end up being what we do?
For example: right now, during this pandemic, we have government medical officers the world over dictating what are effectively bylaws to cities, and what are effectively regulations to businesses. In a climate crisis — say, a country entering permanent heat wave, becoming entirely non-arable where it previously relied on internal food sourcing — could we potentially see see government ecological officers of such countries given similar powers? What would then happen at the UN, if some of those countries were prominent members?
Etc.
Keep in mind that I’m a science-fiction novelist, not a futurist. I care a lot more about the could-happen than the will-happen. :)
(This would best be done not suddenly over years, but gradually over a century; with each country “losing” land on a schedule, as if a peninsula being eroded away into the sea; while gaining land at the same pace on the other end. Maybe each country could run a big painted cable across the country representing the border in places where it’s otherwise illegible, and then keep moving it along north/southward with each passing year. That would give people time to become wary of the encroaching border and move away, probably taking advantage of some government tax credit for doing so.)
As long as all this is done through negotiated treaties, rather than through war, this sort of mass resettlement seems somewhat like a good idea—even if we don’t experience world-shattering climate change. It’d be a recognition of the fact that some places in the world are (naturally) livable for human beings, while others aren’t. And that people have natural rights, no matter their country of citizenship, to reside in a livable climate. Which means that the people who were already living in not-naturally-livable areas even before recent anthropogenic climate change, would be acknowledged as having the right to resettle somewhere more livable, with governments working to change borders or citizenships to allow them that.