In less than 100 years, strolling from shop to shop along Commercial Street in Portland or running with your dog on Willard Beach in South Portland could become something folks did in the old days. Based on the latest tidal trends, the National Oceanic and Atmospheric Administration predicts that by the year 2100, those areas will be under at least a foot of seawater at high tide on a calm day. Under this grim scenario, Willard Beach would disappear, showing up once in a while as a narrow strip of sand at extreme low tides. The indomitable brick buildings on...