A team of researchers recently studied 120 ice sheets collapses and other factors to put together the history of sea level rise for the past 500,000 years. The researchers found sea levels have changed drastically in the past, due to factors not connected to human interaction, but they do not state current rates of sea level change are normal. The study explains that Earth once had triple the ice it has now, but ice has also been closer to current levels in warmer times.
"In the 120 different events we looked at, ice sheets went from initial change to maximum retreat within 400 years 68% of the time, and within 1,100 years for 95%. In other words: once triggered, ice sheet reduction (and therefore sea level rise) kept accelerating relentlessly for many centuries," writes one of the researchers. They claim the sea level could rise as quickly as 5.5 meters per century, based on what they found from previous eras. Much of the studying was done in the Red Sea, because the Red Sea's salt levels change as sea levels change, so they can see where the sea level was for certain parts of history. They were also able to measure temperature change and CO2 levels by extracting ice cores. The study can be found in the journal Nature Communications.