LONDON—Sea levels may rise by more than two metres for each degree Celsius of global warming the planet experiences over the next 2,000 years, according to a study by researchers in five countries.
The research, published Monday in the Proceedings of the National Academy of Sciences, attempts to iron out the impact of short-term fluctuations in sea levels, examining changes over a longer term for which forecasts are more certain.
The findings signal that melting of ice in the Antarctic will take over from thermal expansion, where warmer water occupies more space, as the main cause of rising seas. In the worst-case scenario examined, a temperature gain of four degrees Celsius would result in seas rising by about nine metres since industrialization began in the 18th century.
Researchers from Germany, the United States, Canada, Spain and Austria contributed to the study. They used computer models and analysis of past trends in sea levels derived from sediments and raised ancient shorelines to make their predictions.
“Continuous sea-level rise is something we cannot avoid unless global temperatures go down,” Anders Levermann, the lead author of the study, said by email from the Potsdam Institute for Climate Impact Research in Germany, where he is based.
“We need to adapt,” Levermann said. “Sea-level rise might be slow on time scales on which we elect governments, but it is inevitable and therefore highly relevant for almost everything we build along our coastlines, for many generations to come.”
Temperatures already have climbed about 0.8 degree and seas have risen about 17 centimetres since the Industrial Revolution, according to the United Nations. When temperature gains reach one degree, the world will be committed to sea levels about 2.3 metres higher over two millennia, according to the study in the journal of the Washington-based National Academy of Sciences.
About 1.6 metres of that will come from ice melting in Antarctica, 40 centimetres from the natural expansion of the sea as it gets warmer, 20 centimetres from mountain glaciers and 10 centimetres from Greenland, it said.
In the four-degree scenario, Antarctica would add 4.8 metres to sea levels over 2,000 years, thermal expansion would contribute 1.7 metres and mountain glaciers and small ice caps would add 45 centimetres.
Greenland would contribute 2.1 metres, though it would be destabilized to the point that a further 4.9 metres is possible if all the ice there melted over the next few thousand years.