You need to imagine a future where this ocean is populated and as active as all the other planet’s coastlines.
That’s more a perspective of the coming centuries then it is of the coming decades though. It’s not like migration follows gradually and in line with each degree the temperature rises. Also in that scenario the temperature on the Pacific coast lines will likely rise much more then the temperature on the Atlantic coast lines because of the likely collapse of the AMOC (meaning the red line might even expand further south, perhaps making european migration away from the North Pole more likely then migration towards it).
That’s more a perspective of the coming centuries then it is of the coming decades though. It’s not like migration follows gradually and in line with each degree the temperature rises. Also in that scenario the temperature on the Pacific coast lines will likely rise much more then the temperature on the Atlantic coast lines because of the likely collapse of the AMOC (meaning the red line might even expand further south, perhaps making european migration away from the North Pole more likely then migration towards it).