I think this is the much more likely political result of climate change. Yes, northern states’ population might increase if it we reach the point where people are routinely dying of heat in the South and outdoor labor and recreation are severely restricted. But at that point, the country will have already undergone a massive rightward shift as people fight over dwindling resources and against the migrants, whether they are immigrants from other countries or climate refugees from the US South.
I’m not convinced people who can afford air conditioning will move north to avoid the heat. Air conditioning is much cheaper than heating, and global warming won’t be enough to offset that cost in the north.
That’s not to dispute the premise here entirely. We can imagine more and more super-hurricanes making people walk away from certain southern cities, as many did following Katrina. As Florida becomes flooded, uninsurable and hurricane-prone, its residents might just walk away. Air conditoning could make a hotter Atlanta livable for quite some time, but we get utter chaos if the heat makes the airport tarmac too soft to operate (as has already happened in Phoenix multiple times).
I don’t know what that means for migration. I don’t think rural southerners could afford to live in northern blue states and probably wouldn’t want to. Keep in mind the Appalachians and Midwest are plenty cool and plenty affordable. They could simply move to the breezier parts of Tennessee or Ohio.
I think one of the things that I’ve noticed is that a lot (most?) of the West Coast migrants to Texas seem to be primarily right-wing types who come here because of the political climate (no gun regulation, etc…) and because they perceive there to be a lower tax burden.
I’m not sure that’s so, unless you don’t actually own any property, as our property taxes are very high relative to elsewhere in the US, and our sales taxes are as well. But no income tax, so there’s that.
Moving to Rochester would probably get you a larger house, but not much else on their list. So for them, Texas is perceived to be cheaper and more friendly than say… Washington or California, but maybe not as unfriendly as New York might be. I don’t know if climate has much to do with it; Texas is certainly more harsh in many climactic ways than most of California (extremely hot summers, violent weather (tornadoes, hurricanes and floods) and some parts are even prone to winter storm weather from time to time. From what I understand, Rochester is mostly cold and snowy in the winters, but otherwise pretty mild.