In a minor Ice Age, the tropical will become temperate, the temperate will become arctic. The arctic will become frozen death. So as long as humanity moves towards the equator, everything should be fine. After the coming States revolution, I suggest we invade Mexico, Cuba and Central America. After all, who will stop a 100 million strong army.
Especially if we have nuke plants in the North, so our bases and supply depots will be hard to reach for those without lots of fuel.