Sea levels have been rising faster since the beginning of the 20th century than at any other time in the past 4,000 years.

Researchers at New Jersey's Rutgers University attribute this primarily to the warming of the oceans and the melting of glaciers and ice sheets. Ice loss is accelerating significantly, particularly in Greenland.

While sea levels rose only slowly in the 19th century, they have already risen by an average of 1.5 millimeters (1/20th of an inch) per year between 1990 and 2020. Earlier fluctuations were more pronounced, but occurred over much longer periods of time.

Local factors also play a role: in cities such as Shanghai and Jakarta, land subsidence caused by construction activities and groundwater extraction has resulted in parts of these areas now lying below sea level.