I don't know if it's true or not, but I've read that when places become more temperate because of climate change, they're still not very livable because there's no soil capable of supporting crops.
It takes decades for the soil to get invaded by bacteria, grasses, shrubs, trees... but eventually they will get there. With a little human help, it can get done even faster.
The warming process is blazing fast on geological scales, but for example sea levels are not expected to reach the top of the Statue of Liberty for at least another 500 years, so on a human scale it's more than enough time to build whole cities, generate fertile top soil, or to organize scuba trips to the 9/11 memorial and put warning signs at sub tunnel entrances.