How long have sea levels been rising? How does recent sea-level rise compare to that over the previous centuries?
Between about 21,000 years and about 11,700 years ago, Earth warmed about 4 degrees C (7.2 degrees F), and the oceans rose (with a slight lag after the onset of warming) about 85 meters, or about 280 feet. However, sea levels continued to rise another 45 meters (about 150 feet) after the warming ended, to a total of 130 meters (from its initial level, before warming began), or about 430 feet, reaching its modern level about 3,000 years ago.
This means that, even after temperatures reached their maximum and leveled off, the ice sheets continued to melt for another 8,000 years until they reached an equilibrium with temperatures.
Stated another way, the ice sheets’ response to warming continued for 8,000 years after warming had already ended, with the meltwater contribution to global sea levels totaling 45 additional meters of sea-level rise.
From about 3,000 years ago to about 100 years ago, sea levels naturally rose and declined slightly, with little change in the overall trend. Over the past 100 years, global temperatures have risen about 1 degree C (1.8 degrees F), with sea level response to that warming totaling about 160 to 210 mm (with about half of that amount occurring since 1993), or about 6 to 8 inches. And the current rate of sea-level rise is unprecedented over the past several millennia.