You can get a slight hint as to what it would look like by looking to the pacific northwest, Canada, Alaska. The northern pacific ocean has a "Gulf Stream" called the Kuroshio. However, there is no appreciable meridional overturning in the north pacific. Thus north-west portion of north america is colder than Europe at the same latitude. Roughly.

I've lived there. Let's say I like the European climate a bit better.

Northwest Russia is habitable. Not that pleasant, but habitable.

For a relatively limited number of people and with a standard of life that doesn't compare to western/northern Europe. It will be 'a bit of an adjustment' to put it euphemistically.

I've lived in Northern Canada, which is somewhat comparable to Northwest Russia and sure, it's doable, but civilization as it currently exists in the countries that are exposed to this will cease, the present day number of inhabitants will be unsupportable.

Just trying to imagine the UK with a climate shift like that and the mind boggles. What works for Iceland will not work for the UK without a massive reorientation, which is probably a friendly way of writing 'mass die-off'.

Novosibirsk, Russia is 1m+ city... with some effort you can live. Russians are obsessed about populating their country all over even in the most inhospitable places vs Canadians who are just fine with living south of 60th parallel.

Go ask them how many of them would like to move family and all to Paris or Amsterdam and how many people from Paris or Amsterdam would like to move to Novosibirsk.

I've lived in Northern Canada. Snow isn't nearly as much fun as it is cracked up to be when there is 6+ months of it in some years (I recall one year where the snowplow went on the tractor in October and we had the last snow in June).

Those areas are well outside the ones where humans feel comfortable most of the time and don't underestimate the energy budget on a per-person basis required to make those places habitable to begin with.

Gamify it. Make them think it's practice for settling on some ice planet! Sell tickets via a lottery for the real thing some time really soon.

Northern Europe doesn't have ownership of Southern Europe, so they may not be comparable in the sense that habitability is somewhat subjective in the age of modern logistics.

That’s the thing. Growing food may be tough up there, but otherwise you can still have thriving cities if you have the capital to build appropriate infrastructure.

And are willing to spend a very high amount of energy per person.