Rising sea levels are likely to be faster and higher 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 that sea levels are not expected to rise beyond 1.1 meters (3.6 feet) by 2100.
But climate researchers at the Niels Bohr Institute at the University of Copenhagen believe that levels could rise up to 1.35 meters by 2100, in the worst warming scenario. When they used historical data on sea level rise to validate several models on which the IPCC made its assessment, they found a discrepancy of about 25 cm, they said in an article published in the journal Ocean Science.
The researchers said the models used by the IPCC were not sensitive enough, based on what they described as a “reality check” test.
“It is not good news to believe that previous predictions are very low,” said climate change scientist Aslak Grinsted, co-author and associate professor at the Niels Bohr Institute.
“The models used to base predictions of sea level rise are currently not sensitive enough,” he said. “To be more clear, they don’t hit the target when we compare them to the rate of sea level rise that we see when comparing future scenarios with observations going back in time.”
However, he hoped that his test method could be used to restrict models, make them more reliable and reduce uncertainty. He said the article was sent to IPCC sea level scientists.
The increase forecasts used by the IPCC are based on a “puzzle” of models for ice sheets, glaciers and thermal expansion or sea heating. The higher the temperature, the higher the sea level.
But, Grinsted said, sometimes only a limited amount of data was available for models to be tested. There was virtually no data on the Antarctic melt rate before satellite observations in the 1990s, he said. Grinsted found that while the individual data, when tested back in time, from 1850 to 2017, reflected the actual rise in sea level, when the data was combined the predictions were very conservative.
“We have better historical data for overall sea level rise, which, in principle, allows for a test of the combined model puzzle,” said Grinsted.
The research team at the Niels Bohr Institute hopes that their method for validating future scenarios looking to the past can gain a basis for how sea level rise will be analyzed.
Jens Hesselbjerg Christensen, professor in the ice, climate and geophysics section of the institute and co-author of the article, said: “We hope that this new comparison metric will be adopted and can become a tool that we can apply when comparing different models.”