Worst-case scenario sea levels predicted

Sea levels could rise a maximum 1.8 metres this century in the worst-case scenario. An upper limit for the rise has not been calculated before.

The report by the UN’s Intergovernmental Panel on Climate Change (IPCC) in 2013 was based on the best available estimates of future sea levels – but the panel was not able to calculate an upper limit for sea level rise within this century.

Now researchers from the Niels Bohr Institute in Denmark have calculated the risk for a worst-case scenario. The results, which were published in Environmental Research Letters, indicate that at worst the sea level could rise a maximum of 1.8 meters.

There are several reasons for the rise in sea levels, including the melting of the ice sheets, humans pumping more groundwater than can seep back into the ground and the warming of the oceans. The greatest risk is posed by the ice sheets melting, the study found.

Aslak Grinsted, Associate Professor at the Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen, said: “We wanted to try to calculate an upper limit for the rise in sea level, and the biggest question is the melting of the ice sheets and how quickly this will happen.

“The IPCC restricted their projections to using results based on models of each process that contributes to sea levels. But the greatest uncertainty in assessing the evolution of sea levels is that ice sheet models have only a limited ability to capture the key driving forces in the dynamics of the ice sheets in relation to climatic impact.”

Working with researchers from England and China, Grinsted has now devised new calculations. The researchers combined the IPCC numbers with published data about the expectations within the ice-sheet expert community for the evolution, including the risk for the collapse of parts of Antarctica and how quickly such a collapse could take place.

“We have created a picture of the probable limits for how much global sea levels will rise in this century. Our calculations show that the seas will likely rise around 80 cm. An increase of more than 180 cm has a likelihood of less than five per cent,” added Grinsted.

He concluded that a rise in sea levels of more than two meters was improbable, but highlighted that the results only concerned this century.

Photo credit: United Nations Photo/ CC BY-NC-ND 2.0

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