Sea levels could rise up to 20 metres if Paris climate accord isn't followed, NZ study finds

A Victoria University of Wellington-led study published today in a major academic journal has found global sea levels have the potential to rise up to 20 metres under current atmospheric carbon dioxide levels.

Dr Georgia Grant. Source: Victoria University of Wellington.

Research has revealed that 3 million years ago, levels of carbon dioxide in the earth’s atmosphere were similar to today’s levels and subsequently caused a rise in sea levels of as much as 25 metres after a third of Antarctica’s ice sheets melted.

Known as the Pliocene Epoch, temperatures rose between two and three degrees in response to rising levels of carbon dioxide.

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A NIWA-led study discovered sun-warmed waters beneath the world’s biggest slab of ice. Source: 1 NEWS

The study was led by Georgia Grant, a recent Victoria University of Wellington PhD graduate who is now based at GNS Science.

Ms Grant developed a new method of determining the magnitude of sea-level change through analysing the size of particles moved by waves, as part of her PhD research.

The method was applied to the geological archive from Whanganui Basin on the west coast of New Zealand’s North Island, which contains some of the best evidence anywhere in the world for global sea-level changes.

Ms Grant was able to show that during the past warm period of the Pliocene about three million years ago, global sea levels regularly fluctuated between five to 25 metres.

The study, which was funded by the Royal Society Te Apārangi’s Marsden Fund, also involved professor Tim Naish and Gavin Dunbar from the University’s Antarctic Research Centre, as well as other scientists from GNS Science, Victoria University of Wellington and Waikato University, and from the Netherlands, the United States and Chile.

Mr Naish said the study comes with a stark warning. 

"If we do not keep our greenhouse gas emissions in line with the Paris Climate Agreement target of two degrees warming, then we may potentially lose not only the West Antarctic Ice Sheet, but also the vulnerable margins of the East Antarctic Ice Sheet,” he said. 

Of critical concern, added Ms Grant, is that over 90 percent of the heat from global warming to date has gone into the ocean, and much of it into the Southern Ocean which surrounds the Antarctic ice sheet.

"One-third of Antarctica’s ice sheet — equivalent to up to 20 metres sea-level rise — sits below sea-level and is vulnerable to widespread and catastrophic collapse from ocean heating.

"It melted in the past when atmospheric carbon dioxide levels were 400 parts per million (ppm), as they are today," she said. 

“Our new study supports the idea that a tipping point may be crossed if global temperatures are allowed to rise more than two degrees, which could result in large parts of the Antarctic ice sheet being committed to melt-down over the coming centuries. It reinforces the importance of the Paris target."

The study was published today in the journal Nature.