New York Skyline
High-rising buildings sink New York City by 2mm every year. MIKE SEGAR/Reuters

A recent research article published in the Earth's Science edition of Advancing Earth & Space Science suggested that New York City could sink under its own weight in the near future. The article published earlier this month shows how the island burdened by skyscrapers is subsiding by 2mm per year.

The scientists have termed this research the most difficult task because the rate of this subsidence is comparatively new when measured against the urban load of buildings and people, which has been happening for a bigger period. Despite that, they have done thorough research comparing the surface geology of the place from different satellite image sources including GPS or the Global Positioning System and Interferometric Synthetic Aperture Radar.

While the weight of the various high-rising buildings that plague the city is causing the city to sink there might be other critical reasons behind New York's sinking. One of the primary reasons is how the earth is continuously shifting since the time of the ice age impact that happened 10,000 years ago.

What does this mean?

The sinking of New York City means catastrophic changes will be happening in the coming years, which might seem a bit apocalyptic like the 2012 film but in reality will occur with simple changes like rapid rise in sea levels, frequent floods over consistent periods of time.

Sea level rise is eventually going to pose inundation challenges in New York and globally.
Tom Parsons, Geophysicist, U.S. Geological Survey.

Scientists have already underlined how sea levels along the US Atlantic Coast are rising at an alarming rate because of global warming and climate change. The situation is such that this part of the world is experiencing a three to four times more sea level rise than the global average.

How will this study help?

At a time like this, the data from this research is crucial to predict flooding patterns in New York City.

In the research paper, the scientists have already articulated that some areas are sinking at a higher rate than other areas although the median subsidence rate is 1-2 mm per year. Based on that we can easily demarcate the flood risk zones in the city.

The researchers are particularly pointing towards Manhattan where the numerous skyscrapers have burdened the earth to sink at a rate of 2.1 mm per year which is higher than the mean rate of subsidence recorded in overall New York. This means that Manhattan, particularly lower Manhattan, is sinking 0.08 inches yearly, as seen in the Global Positioning System.

What's causing this?

The cause of this sinking isn't man-made alone. Some of it can be attributed to natural geological causes like the movement of ice during the ice age. As the planet became more habitable, especially during the last ice age, the soil that lies underneath the massive ice sheets were sinking, resulting in the upward shift of the landmasses.

When the ice age ended, most of these ice sheets that surrounded the ground all over the world started melting and the landmasses that got tilted upwards began sinking which is continuing even today. Scientists estimate that by the end of 2100, the US East Coast will sink by 48-150 cm. This accounts for 19 to 59 inches of landmass subsiding.

While this was relatively known, scientists wanted to find out the effect of man-made causes. By comparing computer models of different buildings and satellite data they found out that the weight of the buildings is making the city sink by 1-2 mm every year which is in-sync with the ice age earth shifting.

How did they hit upon the idea?

In 2019, Tom Parsons was in Belgium along with his wife and her family when he hit upon the idea while looking at the vast foundation stones of a cathedral in Antwerp, wondering about its effect on the ground.

Parsons reasons that every building causes the ground beneath it to sink or settle a little when the entire construction is completed. The nature of this subsidence depends on the nature of the ground. A softer earth will cause greater subsidence than hard rocks.

This simple geological fact and thinking about the cathedral while on a holiday in Belgium led to the idea of studying the buildings of New York City and their effect on the soil underneath.

How did they do it?

The scientists then calculated the mass of all the 1,084,954 buildings of all five boroughs of New York City. The estimated result was a whopping 763 billion kg or 1.68 trillion lb weight which spanned over an area of 778 sq km or 300 sq mi.

They built computer models of all these buildings and their weight and checked how the soil sank in those models. The models were made keeping in mind the types of soil prevalent in different parts of the city.

When the data from the computer models were tallied with the satellite data of 0.04-0.08 inches or 1-2 mm subsidence per year it matched. At first the scientists thought that this was due to the earth's natural shifting but the difference in the rate of sinking in different areas soiled the evidence towards the role of the buildings in this sinking. However, they haven't ruled out other causes behind this phenomenon and further research is needed.

What's the bottom line?

Sea level rise in New York is about 1 to 2 millimetres per year, so every millimetre of subsidence is equivalent to moving a year ahead in time with regard to rising ocean levels.
Tom Parsons, Geophysicist, U.S. Geological Survey.

The bottom line from this study is that the rate of sinking in New York City is equivalent to the rate of sea level rise. This means we are moving a year into sea level rise with every millimetre of sinking.