You’ve probably heard by now that global sea levels are rising. But in populated coastal towns, only half of that threat is from ocean levels increasing.

The other half comes from something called subsidence – the gradual sinking of the Earth’s surface. 

A new study looked at roughly two-thirds of the world’s coastal population and found that people on densely populated coasts are now experiencing about a quarter inch of relative sea level rise per year. That’s close to double that from climate-driven ocean levels rising alone. 

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When averaged across the world’s coastlines, the rate is nearly one third of that. The difference is where people build. 

About 90% of the world’s coastal population lives in an area that extends along only roughly 10% of the global coastline.

And those populated stretches are the ones disproportionately sinking. 71% of people living in low-lying coastal zones are on land that is sinking. 

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Why is the ground sinking?

Subsidence is driven by various natural and human processes. Natural events such as earthquakes, soil compaction, glacial adjustment, erosion and sinkhole formation can all cause subsidence.   

However, the majority of subsidence is caused by human activities — the removal of water, oil, natural gas or mineral resources out of the ground by pumping, fracking or mining activities. 

For example, when groundwater is pumped out of an aquifer faster than it refills, the sediment layers above it lose the water pressure that was holding them apart. They compact, and the soil settles, sinking the ground above it.  

Southeast Asia is sinking fastest

Jakarta, Indonesia, has the highest average rate of vertical land movement (VLM) in the world, an average of 13.7 millimeters a year — that’s over half an inch a year. And within Jakarta, local VLM varies greatly, with some neighborhoods dropping as much as 1.65 inches a year. 

In fact, it's sinking so fast that Indonesia is planning to move it's capital to a new city, named Nusantara, located over 620 miles away from Jakarta.

Tianjin, China is close behind at 13.5 millimeters (0.53 inches) a year. Bangkok is sinking at a rate of 0.33 inches a year. 

At a national level, Thailand, Bangladesh, Nigeria, Egypt, China and Indonesia are all seeing population-weighted sea level rise of 7 to 10 millimeters (0.27 to 0.39 inches) a year – two to three times the global ocean average.

American cities are sinking too

Some of the U.S. cities sinking the fastest are Houston, Philadelphia, New York and Washington D.C. Though not as dramatically as Jakarta – about a tenth of an inch a year – still enough to matter. 

A 2024 study by several of the same researchers examined 32 major U.S. coastal cities and found that 24 of them are sinking faster than 0.08 inches per year. And by 2050, the study projected roughly an additional 388 to 536 square miles of U.S. land will be exposed to relative sea level rise. 

This puts foundations, buried pipes, runways and rail beds all under stress that engineers didn’t design for. This means storm surge and flooding risk increase across coastal towns. 

Subsidence can be minimized

This may sound discouraging, but there are still ways to minimize subsidence. Unlike the increase in ocean levels, subsidence responds to local decisions on human timescales.

Tokyo is proof of that. Parts of the city were once sinking near 4 inches a year, and in its worst areas, over 9 inches a year.

Japan then began to regulate groundwater pumping and developed alternative water supplies, and the sinking largely stopped. Tokyo's water table went from 190 feet below sea level at its worst back up to 20 to 32 feet below sea level. 

What you can do now

For homeowners living on the coast, there are some things you can do now to prepare. 

Look up your address on FEMA’s flood maps to know what zone you’re in to know what your flood risk actually looks like. Also, check that your flood insurance is current – before the next storm, not after it. 

Miriam Guthrie is an associate meteorologist with weather.com who graduated from Georgia Tech with her undergrad and graduate degrees in Earth & Atmospheric Sciences.