Climate-change researchers are warning that sea levels could rise 30 metres within the next 2000 to 3000 years, and by one metre by the end of the 21st century.
Tim Naish of Victoria University joined a Rutgers University team that took core samples in Virginia, Whanganui and Enewetak Atoll in the Marshall Islands.
The team looked at sea levels three million years ago, when carbon dioxide levels were similar to those today.
Professor Naish says findings based on core samples taken earlier from Antarctica indicated that sea levels would rise between five and 40 metres.
But he says the latest research has has narrowed that down, indicating a rise of between 10 and 30 metres, caused by melting ice sheets and the thermal expansion of water.