That's fine if you want to spend trillions moving the cities of Europe and US to Siberia.
It would be much cheaper, and require far less political co-ordination, to avert the CO2 emissions leading to climate change in the first place.
And even if you do take the incredibly drastic step of moving most of humanity to the Arctic circle, you still have the problem of runaway heating. What are you going to do when the climate changes for the places you have moved to?
Besides, I rather like having a range of different biomes available on my planet.
> That's fine if you want to spend trillions moving the cities of Europe and US to Siberia.
I don't even want to get into thinking why and if Russia [1] would let the people of Europe and the USA in, but that's only about 1 B people. There are many more out there.
[1] The Nordic countries and Canada, and probably the south of Chile and especially Argentina, are similarly well positioned.
You say that like that’s inherently a bad thing.
IIRC (from some other commentor’s previous napkin math), such a change would actually be unlocking a lot more livable/arable land than would be desertified by it. Just counting the tundras in Northern Canada + Northern Russia + Antarctica + Greenland, that’s already more potential arable/livable landmass than the entirety of the US + Europe.
What you should probably highlight, if you want to make an argument like this, is the time scale. If that change occurred over ~100,000 years, it’d probably be a great thing for human civilization, and, though it’d kill off a fair number of animal species, there’d also be time for many new adaptations to occur, so overall biosphere diversity wouldn’t be greatly impacted. The Earth would be different, but not necessarily worse.
It’s the fact that said change has the potential to occur over only ~100 years, that screws the biosphere (including us) over.