As quoted in the Bible, the foolish man built his house upon the sand. Risk concerning the potential destructive power of the sea has been known for as long as historical records have been kept.... that is thousands of years.
Nobody can say how much the sea will rise in the next 50 - 100 years. All we know is that it is rising, insurance companies will soon include additional caveats to protect themselves and at the moment anyone measures an actual material rise rate (above the norm) buyers will run for the hills (literally).
