Michael Kahn recently wrote in Reuters about how the flooding of what is now the Black Sea is related to the emergence of farming in much of Europe. He also brings up the potential impact of future catastrophes on human migrations:

The study also underscores the potential impact rising sea levels may have in the future, the researchers said. An expected one meter rise by the end of the century due to climate change would displace some 145 million people, Turney added.[Noah's Ark flood spurred European farming, November 17, 2007]

Now, there are obvious implications of this for US immigration policy. It means that there is a distinct possibility there will be increased global pressure for humanitarian immigration. We need to look at ways in which more countries can help handle this situation as it emerges—and in which the US has ways to carefully select and assimilate its immigrants that minimize impact on an already strained society.