There’s a simple reason why New York City co-ops and condos remain so expensive and why rents are at all-time highs: the supply of housing units has historically failed to keep up with demand. Now a new force is getting ready to worsen the city’s housing crisis. More than 80,000 housing units in New York City and the southern shore of Long Island could be lost to floods over the next 15 years, according to a new report by the Regional Plan Association, a nonprofit civic organization. And those staggering losses could double by 2070.     Read the article…………………………….