A New Zealand study has used prehistoric data to paint a picture of how climate change will affect sea levels.
The study, from Victoria University of Wellington, looked at the size of particles moved by waves millions of years ago to measure the change in sea level in the Whanganui Basin.
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Lead researcher Dr Georgia Grant told The AM Show it's a new way to see how sea levels have changed in the past.
"It's a new and quite unique record of sea-level change around three million years ago, which was the last time we had 400 parts per million of carbon dioxide in the atmosphere."
According to the data the ice sheets are capable of widespread melting and raising the sea level up to 20 metres under current atmospheric carbon dioxide levels.
Dr Grant hasn't yet mapped how the sea-level change will look across New Zealand, but scientists are working on that.
She said the suggestion of large sea-level rise isn't new though.
"We've been looking at this picture for a while now with the vulnerability of the marine-based margins around the ice sheet, where those parts of the ice sheet that are sitting grounded below sea level bathed in those ocean waters."
There is a chance humanity can avoid a watery fate if emissions are curbed, but there will still be some sea change, Dr Grant said.
"If we manage [the Paris Climate Accord's] target we might reduce that kind of significant retreat but we're still looking at half a metre by the end of the century."