recent Elizabeth Kolbert new yorker piece on miami and flooding http://www.newyorker.com/magazine/2015/12/21/the-siege-of-mi...

The basic problem is the limestone. Because of the limestone, seawalls are essentially useless as the water goes underneath through the porous ground. I think very likely the comments only seem exaggerated to you because it's difficult to imagine with all the people around you driving fancy cars and buying expensive condos, like pre-cupernican difficult.

No one knows how long miami has, but I would bet it's closer to 20 years than 100 years. To be quite honest, I hope it happens sooner rather than later as maybe something like that will start to wake people the fuck up. Doubtful though. There's always another rationalization.