Scientists have modeled a history of the planet’s sea levels spanning back nearly 3,000 years, and concluded that the rate of increase last century “was extremely likely faster than during any of the 27 previous centuries.”
Bob Kopp, a climate scientist at Rutgers University who led the research, said in a statement on his website that he and his collaborators had determined with 95% probability that the rate of sea level increase in the 1900s was faster than during any century since at least 800 B.C.
It is not that seas rose faster before that date, he wrote — but “simply that the reconstruction quality isn’t good enough before then” to say so with the same level of confidence.
Moreover, the study found that without human-caused climate change, the global sea level would have “very likely” changed by between a 3 centimeter (1.18 inch) drop and a 7 centimeter (2.75 inch) rise over the 20th century — rather than the 14 centimeter (5.512 inch) rise that was observed.
The study, conducted by a group of 10 climate scientists from universities around the world, was published Monday in the U.S.’s Proceedings of the National Academy of Sciences.
The authors said it was the first estimate, to their knowledge, of global sea level change over the past 3,000 years based on a “statistical synthesis of a global database of regional sea level reconstructions.”
It used a new statistical framework to combine reconstructions of 1,300 geological sea level changes in 24 locations around the world, along with measurements from 66 “tide gauges.”
The study says the global sea level rose at a rate of 1.4 millimeters (0.05 inches) a year during the 20th century. NASA’s figures, which put the current rate of sea rise at 3.4 millimeters (0.13 inches) a year, suggest sea level rise is only accelerating.
The study’s authors said a “significant” and “historic” acceleration in sea level rise began in the 19th century.
It also found that the 20th century “wasn’t the only time period when temperature and global sea level changed together,” wrote Kopp.
The study found that that the global sea level fell by “a statistically robust” 8 centimeters between 1000 and 1400, a period in which the global temperatures declined by about 0.2°C, he wrote.
An assessment report from the U.N’s Intergovernmental Panel on Climate Change in 2013 found with 95% certainty that human activity was to blame for at least half of climate change in the last half-century.
The report, created from the work of nearly 1,000 researchers worldwide and considered the benchmark study on global warming, projected a rise in global sea levels of 1 to 3 feet (about 30 to 90 centimeters).
But researchers last year suggested those predictions could be too conservative, with ice loss from massive melting ice sheets in Antarctica and Greenland being a major concern.
In December, ministers from 195 countries adopted a legally binding agreement in Paris to fight climate change. The goal of the deal is to help the world abandon fossil fuels this century and, specifically, stop global warming “well below” 2 degrees Celsius and, if possible, below 1.5 degrees.