Sea level rise up to four times global average for coastal communities

Coastal populations are experiencing relative sea-level rise up to four times faster than the global average – according to new research from an international research team that includes Global Climate Forum.

A new study published today in Nature Climate Change is the first to analyse global sea-level rise combined with measurements of sinking land. Climate-induced sea-level rise is a known threat to coastal populations, but the role of land subsidence in influencing relative sea level is less recognised. Recently, sea-level rise around the world’s coasts, including subsidence, averages 2.6 mm/yr. However, coastal residents on average experience sea-level rise four times faster at 7.8-9.9 mm/yr, reflecting that people preferentially live in subsiding areas, especially on deltas and in cities on deltas. Hence, contemporary risks of relative sea-level rise are much worse than previously recognised. Urgent and feasible action is needed to control and mitigate human-induced subsidence in populated areas.

The research team assessed four components of relative sea-level change – climate induced sea-level change, the effects of glacier weight removal causing land uplift or sinking, estimates of river delta subsidence and subsidence in cities. Sea-level measurements were taken from satellite data. The team then weighted their results by population to show their importance to people. The overall analysis used the Dynamic Interactive Vulnerability Assessment (DIVA) model which is designed for understanding coastal management needs.

They found that high rates of relative sea-level rise are most urgent in South, South East and East Asia as the area has many subsiding deltas and coastal flood plains, growing coastal megacities and more than 70 per cent of the world’s coastal population. They also found that over the 20th Century, the city of Tokyo experienced net subsidence of 4m, while Shanghai, Bangkok, New Orleans, and Jakarta, have experienced between 2m and 3m subsidence. In Tokyo, Shanghai and Bangkok the subsidence has been stopped or greatly reduced by reduced groundwater extraction, while in other cities there has been little direct response to reduce subsidence.

Nicholls, R.J., Lincke, D., Hinkel, J., Brown, S. Vafeidis, A.T., Meyssignac, B., Hanson, S.E., Merkens, J.-L., Fang, J. (2021). A global analysis of subsidence, relative sea-level change and coastal flood exposure. Nature Climate Change.