By Kenneth Richard on 23. February 2023
More evidence emerges that modern rates of sea level rise are approximately 20-50 times slower than natural rising rates occurring during deglaciations.
In tropical areas coral reef fossils form terraces, or flat surfaces bordered by ascending sloping surfaces. Terraces are formed at or near sea level, so their relative geological presence can be interpreted as reliably precise proxies for past relative sea levels.
A new study uses fossilized coral evidence from terraces and the elevation of beach rock relative to today to discern sea levels were higher than present from about 7,500 years ago until about 1,500 years ago. Specifically, sea levels were 2.2 to 2.4 meters higher (highstand) than today from 5,500 to 4,200 years ago.
The primary reason sea levels were so much higher was that the Earth’s surface was significantly warmer than it is today throughout most of the last 10,000 years. The water that has in recent centuries been locked up in ice sheets and glaciers on land inhabited ocean basins as recently as a few thousand years ago.
Image Source: Janer et al., 2023
Sea level rise rates of 45-80 mm/yr
Frederikse et al. (2020) and Frederikse et al., 2018 assessed the global rates of sea level rise were effectively the same for the entire 1900 to 2018 period (1.56 mm/yr−¹) as they were from 1958-2014 (1.5 mm/yr−¹). So, about 1.5 mm/yr−¹ is the modern sea level rise rate.
Compare this current value to the rates of sea level rise in the past 20,000 years, or when sea levels rose 120 m out of the last glacial maximum (LGM).
About 14,700 years ago (Meltwater Pulse [MWP] 1A) the seas rose at rates of up to 80 mm/yr−¹, or 8 m per century. This is more than 50 times faster than today’s rates. About 9,000 to 10,000 years ago, sea level rise rates were still 45 mm/yr−¹.
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