We have had other migrations.
Think about the Dust Bowl Days that were documented in the book and movie The Grapes of Wrath. It seems like eons ago, but those days can still happen today and happen sooner rather than later as Americans become climate migrants.
Earlier I blogged on the New York Times article, but here now is The Daily Podcast (which you don't need a subscription to the NY Times to listen to), "How Climate Migration Will Reshape America."
Well worth listening to. I was chatting with a neighbor who noted that American climate refugees will be coming to the Pacific Northwest. He has recommended that his son, temporarily living in South Korea, purchase a home here, since house values are sure to go up as demand escalates with new people seeking an escape from the heat, water shortages, hurricanes, etc. Of course, while escaping climate impacts, they will be moving to a high earthquake risk area.
As noted in the podcast, we are headed for a "new abnormal."