New York City is sinking at a rate of 1 to 2 millimetres a year because of the sheer weight of all its buildings, a study published in the journal Earth’s Future has found.

The city is home to more than eight million people and across the five boroughs, there are more than one million buildings.

Researchers who wrote the study have concluded that the combined weight of all the buildings in New York City is roughly 762 billion kilograms.

The aim of the study was to raise awareness that “every additional high-rise building constructed at coastal, river or lakefront settings could contribute to future flood risk, and that mitigation strategies may need to be included”.

“A deeply concentrated population of 8.4 million people faces varying degrees of hazard from inundation in New York City,” the study wrote.

The report notes that New York faces “significant challenges” regarding flood hazards, with the Atlantic coast of North America facing the risk of sea levels rising three to four times higher than the global average.

“We’re a way off from the ocean simply moving in,” Tom Parsons, a research geophysicist at the US Geological Survey, one of the report’s authors, told CNN.

“But we’ve had a couple of major hurricane events with Sandy and Ida in New York where heavy rainfall caused inundation in the city, and some of the effects of urbanisation have allowed water to come in.”

Dr Parsons also told CNN construction on soft soils and artificial fill is part of the problem too.

Hurricane Ida devastated New York City in 2021. Photo: Getty

Other cities are sinking, too

New York City isn’t the only city in the world that is sinking.

Indonesia was forced to move its capital city due to this very issue.

With Jakarta sinking into the Java Sea, Indonesian officials decided to move the capital to Nusantara, which is in Borneo. The city is set to be inaugurated in 2024.

Some 10 million people live in Jakarta, but it’s expected that one-third of the city will be inundated by 2050. The main reason for Jakarta going under water is uncontrolled ground water extraction, but sea levels rising due to climate change is exacerbating it.

Italy’s Venice is also at risk of going under. While being plagued by flooding events which damaged cultural sites, it has been suggested the city could be under water completely by 2100.

In Bangladesh, Dhaka and Chittagong are both sinking and millions of people have already been displaced.

When speaking to CNN, Dr Parsons noted this was a global issue, not just in coastal areas, but inland areas also.

He pointed to a 2022 study that examined 99 coastal cities across the world and that study concluded in most cities, land is sinking faster than sea levels are rising.

“If subsidence continues at present rates, these cities will be challenged by flooding much sooner than projected by sea level rise models,” the researchers said.

“The most rapid subsidence is occurring in South, South-East, and East Asia. However, rapid subsidence is also happening in North America, Europe, Africa and Australia.”

Human activity, especially groundwater extraction, was the likely main cause of cities sinking, which is why expanded monitoring and policy interventions are needed to minimise the consequences.