The term “underwater” — used frequently to refer to homeowners who owed more on their mortgage than their property was worth — has a more frightening meaning in a study by Zillow.

Zillow’s new analysis of the potential impact of climate change on homes across the country projects that 1.9 million residences could be literally underwater by 2100 if the oceans rise six feet.

That six-foot rise is approximately halfway between the federal government’s estimated “very likely” rise of 4.3 feet by 2100 and an eight-foot or greater rise, the possibility of which the government says “cannot be excluded.” Zillow opted for this midpoint rather than address the different predictions for various areas.

If those projections come true, this would impact 1.8 percent of the country’s housing stock, valued at $916 billion.

While five of the 10 metro areas anticipated to be hardest hit by rising seas are in Florida, New York City is second on the list, with 4.6 percent of its homes, valued at $123 billion. Also on the list is nearby Upper Township, N.J., where 56.6 percent of homes could be underwater by 2100.

Boston, Salisbury, Md., and Virginia Beach are also among the top 10 areas anticipated to be hardest hit by rising sea levels.

Zillow’s analysts point out that while some cities have already invested in systems to protect residents against rising ocean levels, such as a pump system in Miami Beach and a wall around lower Manhattan, suburban and rural areas are less prepared.

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