At the end of the Last Glacial Maximum (~21,000 years ago), sea levels were at their lowest. Between roughly 14,000 and 8,000 years ago, the majority of the rise occurred, with about 90 metres of sea level increase in just 6,000 years, corresponding to an average rate of roughly 15 mm per year.
After this rapid rise, sea levels continued to increase more gradually, adding another 30–40 metres over the following several thousand years, reaching near-modern levels around 3,000 years ago. From about 3,000 years ago until the pre-industrial period, sea levels were relatively stable, with only minor fluctuations.
From the IPCC report archive (archive.ipcc.ch/ipccreports/tar/wg1/409.htm😞
Based on tide gauge data, the rate of global average sea level rise during the 20th century is in the range 1.0 to 2.0 mm/yr, with a central value of 1.5 mm/yr
Based on the few very long tide gauge records, the average rate of sea level rise has been larger during the 20th century than the 19th century.
No significant acceleration in the rate of sea level rise during the 20th century has been detected.