miami
Elizabeth Kolbert has a good discussion on the end of Miami due to climate change. There's almost no way around this conclusion, not with Miami's limestone allowing water to flow.
Between having 2.4 million people living at six feet above sea level or less and a nuclear power plant ready to be inundated with sea water, watching the United States'.
If you haven't read this Rolling Stone piece on the forthcoming erasure of Miami and all of south Florida from the face of the Earth because of rising sea levels, you should. It's happening and most of us will live to see it.