My guess would rather be that they neither heard about the ice age scare nor the global warming craze, but they simply saw that water is coming, that floods are getting more numerous and that it's safer to pack up and GTFO.
Some people don't need no statistics to know when to flee some place. Wet feet are more convincing than any amount of statistics.
At 6 feet above seal level, how can you even tell floods are more numerous? High tide is over 5 feet. At least once a month, you are going to get flood even if there is no significant weather.
They started fleeing the encroaching waters back in the 1970s when the sea level was still dropping.