NEW YORK — If rising oceans aren’t worrisome enough, add this to the dangers facing New York City: The metropolis is slowly sinking under the weight of its skyscrapers, homes, asphalt and humanity.
New research estimates that the city’s landscape is sinking at an average rate of 1 to 2 millimeters per year, a phenomenon referred to as “subsidence.”
That natural process happens everywhere as land is compacted, but a study published this month in the journal Earth’s Future sought to assess how the city’s massive weight is speeding things up.
More than 1 million buildings are spread across the city’s five boroughs. All of those structures were calculated to press about 1.7 trillion tons (1.5 trillion metric tons) of concrete, metal and glass — the mass of about 4,700 Empire State Buildings — into the earth.
The rate of compression varies across the city. Midtown Manhattan’s skyscrapers are mostly built on bedrock, which compacts very little, while parts of Brooklyn, Queens and downtown Manhattan rest on loose soil and sink faster, the study found.
Although the process is slow, parts of the city will eventually be under water, said lead researcher Tom Parsons of the US Geological Survey.
“It’s inevitable. The land is going down and the water is coming up. At some point, those two conditions will meet,” said Parsons, whose job it is to predict dangerous events from earthquakes and tsunamis to incremental changes to the land beneath us.
But there’s no need to invest in life preservers, Parsons assured.
The study indicates that buildings themselves contribute to the changing landscape, he said. Parsons and his team of researchers reached their conclusions using satellite imaging, data modeling and a number of mathematical assumptions.
It would be hundreds of years – and precisely when is unclear – before New York became America’s version of Venice, which famously plunges into the Adriatic Sea.
But some parts of the city are at risk.
“There’s a lot of weight there, there’s a lot of people there,” Parsons said of Manhattan. “In the southern part of the island the average elevation is only 1 or 2 meters (3.2 or 6.5 feet) above sea level – it’s very close to the water table, so it’s a deep concern.”
Because seas rise at the same rate as land sinks, Earth’s changing climate could accelerate the timeline for parts of the city to disappear under water.
“It doesn’t mean we have to stop building. It doesn’t mean buildings are the only cause. There are a lot of factors,” Parsons said. “This needs to be identified early before it becomes a big problem.”
Already, New York City is at risk of flooding, as massive storms can cause seas to surge inland or torrential rains to inundate neighborhoods.
As demonstrated by Superstorm Sandy a decade ago and the still powerful remnants of Hurricane Ida two years ago, the resulting flooding can have devastating and deadly consequences.
“From a scientific perspective, this is an important study,” said senior researcher Andrew Kruskiewicz of Columbia University’s School of Climate, who was not involved in the research.
Its findings can help inform policymakers as they develop plans to combat or at least prevent rising tides.
“We cannot sit and wait at the critical threshold for sea-level rise, because waiting means we miss out on taking anticipatory action and preparedness,” he said.
New Yorkers like Tracy Miles may be incredulous at first.
“I think it’s a manufactured story,” Miles said. He thought back to the sailboats bobbing along the water’s edge in downtown Manhattan. “We have an overabundance of skyscrapers, apartment buildings, corporate offices and retail space.”
New York City isn’t the only place to sink. San Francisco exerts considerable stress on the ground and the region’s active earthquake faults. In Indonesia, the government is preparing to retreat from Jakarta, which is sinking into the Java Sea, for a new capital to be built on high ground on a completely different island.
