Sea level rise is likely to be faster and greater than previously thought, according to researchers who say recent predictions are inconsistent with historical data.
In its most recent assessment, the Intergovernmental Panel on Climate Change said sea levels are unlikely to rise above 1.1 meters by 2100.
But climate researchers at the University of Copenhagen’s Niels Bohr Institute believe levels could rise as high as 1.35 meters by 2100, in the worst case of warming. When they used historical data on sea-level rise to validate several models on which the IPCC relied to make its assessment, they found a deviation of about 25 cm, they said in a paper published in the journal Ocean Science.
The researchers said the models used by the IPCC were not sensitive enough, based on what they describe as a “reality check” test.
“It’s not great news that we think the previous forecasts are too low,” said climate change scientist Aslak Grinsted, a co-author and associate professor at the Niels Bohr Institute.
“The models currently used to base sea level rise forecasts are not sensitive enough,” he said. “To put it plainly, they don’t hit right when we compare them to the rate of sea-level rise we see when we compare future scenarios with observations going back in time.”
However, he hoped their testing method could be used to narrow down models, make them more credible, and reduce uncertainty. He said the document had been sent to the IPCC scientists at sea level.
The rise forecasts used by the IPCC are based on a “jigsaw puzzle” of models for ice sheets, glaciers and thermal expansion or warming of the sea. The more the temperature rises, the higher the sea level becomes.
But, Grinsted said, there was sometimes only a limited amount of data available for the models to test on. There was practically no data on Antarctica’s melting rate before satellite observations in the 1990s, he said. Grinsted found that while individual data, when tested backwards in time, from 1850 to 2017, reflected actual sea level rise, while the predictions were too conservative when the data was combined.
“We have better historical data for sea level rise in total, which basically allows us to test the combined puzzle of models,” said Grinsted.
The research team at the Niels Bohr Institute hopes that their method of validating future scenarios by looking in the past can gain a foothold in the analysis of sea level rise.
Jens Hesselbjerg Christensen, professor in the institute’s department of ice, climate and geophysics and co-author of the paper, said: “We hope that this new benchmark for comparison will be adopted and become a tool we can apply in comparing different models. “