At this rate, the city is sinking far faster than sea levels are rising to meet it. "In some cities, we're seeing subsidence of a few centimetres a year," says Steven D'Hondt, professor of oceanography at the University of Rhode Island in Narragansett. Some cities around the world – such as Jakarta, capital of Indonesia – are sinking far faster than others.
( Learn more about how concrete has become the material that defines our age.)Ĭan anything be done to halt these cities – which between them have hundreds of millions of residents – from sinking into the sea? The scale of this infrastructure is vast: in 2020 the mass of human-made objects surpassed that of all living biomass. There is a wide range of reasons for why coastal cities are sinking, but the mass of human infrastructure pressing down on the land is playing a role. New York City, says Parsons, "can be seen as a proxy for other coastal cities in the US and the world that have growing populations from people migrating to them, that have associated urbanisation, and that face rising seas".
"That relaxation causes subsidence," says Tom Parsons, a research geophysicist at the Pacific Coastal and Marine Science Center of the USGS in Moffett Field, California and one of the four authors of the study.īut the enormous weight of the city's built environment worsens this subsidence, Parsons says.Īnd this is a global phenomenon. Relieved of the weight of ice sheets, some land on the Eastern Seaboard is expanding, while other parts of the coastal landmass, including the chunk on which New York City lies, seem to be settling down. New York has already been suffering subsidence since the end of last ice age. That may not sound like much, but over a few years it adds up to significant problems for a coastal city.
And that is concerning experts – add the subsidence of the land to the rising of sea levels, and the relative sea level rise is 3-4mm (0.12-0.16in) per year. That ground, according to a study published in May, is sinking by 1-2mm (0.04-0.08in) per year, partly due to the pressure exerted on it by the city buildings above.
Nor does it include the transport infrastructure that connects them, nor the 8.5 million people who inhabit them.Īll that weight is having an extraordinary effect on the land on which it is built. While that figure involves some generalisations about constriction materials, that prodigious tonnage does not include the fixtures, fittings and furniture inside those million-odd buildings. On the 300sq miles (777sq km) that comprise New York City sit 762 million tonnes (1.68 trillion pounds) of concrete, glass and steel, according to estimates by researchers at the United States Geological Survey (USGS). The Tower Building is long gone – its plum spot on Broadway was taken in 1914 – but its erection marked the beginning of a construction spree that still has not stopped. It was an 11-storey building that, thanks to its steel skeleton structure, is thought of as New York City's first skyscraper. On 27 September 1889, workers put the finishing touches to the Tower Building.
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