What we get is every single existing ocean port city (which is a lot of the largest cities) being threatened by more frequent flooding. They're all right at sea level, because that's where you build port cities. Not all of these cities really depend on being ports any more, but that's how they became major population and business centers.

They don't just pick up and move something like that. There's no place you can say, "Oh, they're going to move New York over to X, so I'll buy land there now". Even if they did for some reason decide that it was so bad they had to abandon New York (or Charleston or San Francisco or lots of others), there's no one place that it goes. The whole human geography of it changes.