Motley: You're likely right.  We will spend hundreds of billions attempting to "defend" these low lying areas with dikes, dams, chewing gum or whatever is available.  That decision regarding "uninhabitable" will ultimately be made by the rising sea.  It's not going to be pretty..

For ten years we owned a cabin in a low lying (flood plain) area near the mouth of one of our beautiful Oregon rivers.  The cabin was built on "pilings" to get it above the hundred year flood plain level.  Then one year we had high tides, lots of rain and a storm surge.  For the first time in anyone's memory, the water was below our deck.  We didn't get flooded, but we got the "message."  We sold the cabin.  I fear more and more "ocean front" properties will change status and be "ocean" properties. 

 Some will accuse me of "the sky is falling" talk.  That's OK, ....I take global warming very seriously and feel it's going to increasingly impact our lives.  and, not for the better.  regards, Gary