See my post below where I link to actual data on sea level rise rate. The ice caps don't melt instantaneously there's not enough energy in one summer to do that. The fastest it ever rose was 3 cm a year during a 1000 year period. Even at 3 cm a year you can build new buildings on higher ground as the water advances and never lose a beat. Especially when we're talking an era when most homes were built out of bones and deerskin and maybe clay. Without metal they couldn't even chop wood but even wood buildings go up rather quickly. I just fail to see how we could believe our ancestors made it through several ice ages, mastered fire, avoided being eaten by saber tooth tigers and hunted wooly mammoths and populated the whole globe but failed to avert a 3cm a year sea level rise.