New York City is sinking by up to 2mm each year on average due to the sheer weight of its buildings, with some areas plunging at double this rate, research has found.
A new study, published in the Earth’s Future journal, warns the US city - which has a “deeply concentrated population of 8.4 million people” - faces “varying degrees of hazard from inundation”.
Researchers say the risks will be shared by other coastal communities around the world as global temperatures rise and the city has to “get planning” for extreme flooding in the future.
The sinking is causing sea levels to rise even more, with the sea level off New York’s coast up to nine inches higher than it was in 1950. This is mostly due to “the slowing of the Gulf Stream and New York’s sinking land” which is causing “major issues” researchers say.
The researchers calculated that the city’s structures, including the famous Empire State Building and Chrysler Building, weigh a total of 1.68tn lbs - roughly equivalent to the weight of 140 million elephants.
Many of New York City’s largest buildings sit upon solid bedrock, but there is a mixture of other sands and clays that have been built over which is adding to a sinking effect.
The sinking effect is naturally occurring along much of the US east coast as the land is reacting to the retreat of huge glaciers following the end of the last ice age. Between 20,000 and 95,000 years ago, the Laurentide Ice Sheet covered most of northern North America and levered the land upwards.
Professor of Earth and Planetary Sciences Peter Huybers said “the mid-Atlantic crust is still subsiding” thousands of years after the ice has gone.
Tom Parsons, a geophysicist at the US Geological Survey, who led the new research told the Guardian the sinking is “not something to panic about immediately” but warned of an increased risk of flooding in the future.
He said: “The softer the soil, the more compression there is from the buildings. It wasn’t a mistake to build such large buildings in New York but we’ve just got to keep in mind every time you build something there you push down the ground a little bit more.”
In 2012, New York was hit by Hurricane Sandy then in 2021 Hurricane Ida flooded areas of the city where at least 14 people were killed as basement apartments suddenly filled with water.
Mr Parsons said New York and other coastal cities “have to get planning for this.” He added: “If you get repeated exposure to seawater, you can corrode steel and destabilise buildings, which you clearly don’t want. Flooding also kills people, too, which is probably the greatest concern.”