According to researchers who, according to recent predictions, are inconsistent with historical data, sea levels are likely to be faster and greater than previously thought.
In its most recent assessment, the Intergovernmental Panel on Climate Change said sea levels are unlikely to rise by more than 1.1 meters (3.6 feet) by 2100.
However, climate researchers from the Niels Bohr Institute of the University of Copenhagen believe that levels could rise by 2100 to 1.35 meters, in the worst case. When they used historical data on sea level to validate the various models the IPCC relied on, they found a difference of about 25 cm, they said in an article published in the journal Ocean Science.
According to the researchers, the models used by the IPCC are not sensitive enough, based on what they described as a “reality test”.
“It is not good news that we believe the forecasts are too low sooner,” said climate change scientist Aslak Grinsted, an associate author and associate professor at the Niels Bohr Institute.
“The models currently used to base the prediction of sea level rise are not sensitive enough,” he said. “To make it clear, they do not hit the point when we compare it to the rate of sea level we see when we compare future scenarios with observations going back in time.”
However, he hoped that their testing method could be used to limit models, make them more credible and reduce uncertainty. He said the article was sent to IPCC scientists at sea level.
The rise forecasts used by the IPCC are based on a “puzzle” of models for ice sheets, glaciers and the thermal expansion or warming of the sea. The more the temperature rises, the higher the sea level will become.
But, Grinsted said, there was sometimes only a limited amount of data available to test on the models. There was virtually no data on the melting rate for Antarctica before satellite observations in the 1990s, he said. Grinsted found that although the data were tested backwards from 1850 to 2017, reflecting the actual sea level rise, but that the forecasts were too conservative when the data were put together.
“We have better historical data for the total sea level rise, which in principle allows a test of the joint puzzle of models,” Grinsted said.
The research team at the Niels Bohr Institute hopes that their method of validating future scenarios by looking at the past can gain a foothold in the analysis of sea level.
Jens Hesselbjerg Christensen, a professor in the Department of Ice, Climate and Geophysics at the institute and a co-author of the article, said: “We hope that this new benchmark will be adopted and become a tool we can used to compare different models. “