Antarctic’s ice melt will cause 30cm sea level rise

New modelling shows melting Antarctic and Greenland ice will raise sea levels by almost 40 centimetres in the next 80 years if emissions are not curbed.

The Antarctic ice in particular will contribute almost three-quarters of that rise (nearly 30cm), though those impacts are expected to mostly be seen in the latter half of this century.

The Nasa-led research, which involved scientists from Crown research institute GNS Science and Victoria University of Wellington, confirmed estimates from earlier, less sophisticated modelling were correct. Sea levels could rise as much as 84cm by 2100 – when taking into account all causes – if emissions continue as they are today.

Sea level rise will have devastating effects on coastal communities, including putting them at risk of inundation during storm surges.

A 2019 study estimated about 71,000 New Zealanders live less than 1 metre above current sea level, and nearly 240,000 live less than 2mabove the high tide line.

Some Kiwis are already moving away from the ocean because of concerns about rising seas, while storm surges like those from ex-tropical cyclones Fehi and Gita in 2018 have already flooded low-lying communities.

Around the globe, about 230 million people live less than 1m above sea level, while about 1 billion people live less than 10m above the current high tide mark.

GNS scientist Dr Dan Lowry, who contributed to the research, said while centimetres sounded like a small amount, it had to be thought of in terms of how it would be affected by extreme events and storm surges.

A small increase in the sea level would allow storm surges to reach much further inland.

Lowry said about 9cm of the predicted rise under current emissions came from the Greenland ice sheets, with the remainder from Antarctica.

Greenland was a more immediate issue, with Antarctica likely to become a problem later in the century. The figures for Greenland also had a stronger consensus in the scientific community, as the surface melting seen today was more easily measured.

In Antarctica, much of the ice being lost was taken by the sea below, a process that was less understood and would depend on the circulation of ocean currents. Scientists are drilling through the ice in an attempt to better understand what is happening.

Lowry said if all the ice in Antarctica melted, it would raise the global sea level by about 58m. Modelling showed the West Antarctic ice sheets might have stability issues in the future, but the eastern sheets were expected to get more snow in the future.

That mass of ice was enough to create its own gravitational field, which pulled nearby water towards it, he said.

As ice was lost, the gravitational pull would decrease, and the ocean would be spread more evenly around the world. The further a place was from the ice sheets, the more they would be affected by this.

Lowry said gravitational pull was an important aspect of the expected sea level change.