As if the rising oceans weren’t problem enough, New York City faces an additional risk: the metropolis is slowly sinking under the weight of its skyscrapers, houses, asphalt, and humanity itself.
New research estimates that the mass of the city is sinking at an average of one to two millimeters a year, known as “subsidence.”
That natural process occurs everywhere as the earth compresses, but the report published this month in Earth’s Future magazine attempted to estimate how the process is accelerating due to the sheer weight of the city.RELATED
There are more than a million buildings spread across the five neighborhoods of the city. The research team calculated that all these structures add about 1.5 trillion tons of concrete, metal and glass, about the mass of 4,700 Empire State Buildings, pressing down on the earth.
The compression rate varies depending on the part of the city. Midtown Manhattan’s skyscrapers are mostly built on rock, which compresses very little, while parts of Brooklyn, Queens and midtown Manhattan are on looser soil and sink faster, the study said.
Although the process is slow, study director Tom Parsons of the US Geological Survey said several parts of the city will be under water at some point.
“It is unavoidable. The ground is going down and the water is rising. At some point, those two levels will meet,” said Parsons, whose job it is to anticipate dangerous events caused by earthquakes, tsunamis or progressive changes in the subsoil.
But there’s no need to invest in life preservers yet, Parsons said.
The report simply points out that the buildings themselves contribute, albeit partially, to the change in the landscape, he said. Parsons and his team’s researchers used satellite imagery, simulation models and a lot of mathematical assumptions to reach their conclusion.
It will be hundreds of years – exactly how many is unclear – before New York becomes America’s version of Venice, sinking into the Adriatic Sea.
But there are parts of the city where the risk is greater.
“There’s a lot of weight there, a lot of people there,” Parsons said of Manhattan. “The average elevation in the southern part of the island is only one or two meters above sea level, it’s very close to the water line, so it’s a serious concern.”
With the ocean rising at a rate similar to the land sinking, the planet’s changing climate could speed up the timeframes for parts of the city to disappear under water.
“It doesn’t mean we should stop building buildings. It does not mean that the buildings themselves are the only cause of this. There are many factors,” Parsons explained. “The purpose was to flag this up early before it became a bigger problem.”
New York City is already at risk of flooding from huge storms that can drive the ocean ashore or drench neighborhoods with torrential rain.
The flooding they cause could have deadly and destructive consequences, as demonstrated by Superstorm Sandy a decade ago and the still-potent remnants of Hurricane Ida two years ago.
“From a scientific perspective, this is an important study,” said Andrew Kruczkiewicz, a senior researcher at Columbia University’s School of Climate, who was not involved in the study.
Their findings can help inform policy makers as they plan to combat or at least anticipate the rising tides.
“We cannot sit by and wait for sea level rise to reach a tipping point,” he explained, “because waiting would mean that we might miss the opportunity to take anticipatory and preparedness measures.”
New Yorkers like Tracy Miles can be incredulous at first.
“I think it’s a made-up story,” Miles said. He then he thought about it as he looked at the sailboats bobbing on the water next to midtown Manhattan. “Yes, we have a huge number of skyscrapers, apartment buildings, company offices and shops.”
New York is not the only place that is sinking. Also San Francisco puts considerable pressure on the ground and active faults in the region. In Indonesia, the government is preparing for a possible move from Jakarta, which is sinking in the Java Sea, to a new capital built on higher ground on a different island.