That鈥檚 according to a in the journal Science.

The study by Zurui Ao, Xiaimei Hu, Shengli Tao and others at South China Normal University, used radar observations from satellites to track ground deformation.

Radar can detect changes of just millimetres per year in ground level. They used the technology to determine the extent of land subsidence across 82 major cities in China from 2015 to 2022.

The study found that of the examined urban lands, 45% are subsiding faster than 3mm per year and 16% are subsiding faster than 10mm per year, affecting 29% and 7% of the urban population, respectively.

The subsidence appears to be due to factors including the weight of buildings and groundwater withdrawal, the study said.

It forecast that by 2120, 22% to 26% of China鈥檚 coastal lands will have a relative elevation lower than sea level because of the combined effect of city subsidence and sea-level rise.

Robert Nicholls at the Tyndall Centre for Climate Change Research at the University of East Anglia told that the report showed that it was a national problem for China but added, 鈥淎nd it is a microcosm of what is happening around the rest of the world.鈥�

Nicholls said vulnerable cities could learn lessons from Tokyo, which sank by about 5m until it banned groundwater extraction in the 1970s.

He added that subsidence mitigation measures would only go so far and that adaptation works and the construction of dykes could be required in the future.