Tamu, 28, is likely to see that traumatic transition during his lifetime, according to a landmark UN report on oceans and Earth's frozen regions, released this week.

Even before the creeping global waterline covers this low-lying atoll between Australia and Papua New Guinea, it will probably be rendered inhabitable by a tropical storm engorged by rising seas, or salt-water infiltration.

"We see first-hand the impact of climate change in rising sea level, coastal erosion," Tamu told AFP phone from New York, where he had gone to bear witness as world leaders gathered in a climate summit.

"We have a deep connection -- culturally, spiritually -- with the land that will be lost."

Confronted with this grim future, everyone on Warraber -- and hundreds of similarly situated tropical islands worldwide -- is confronted with a choice.

But for Tamu and his family, "leaving is not an option," he said emphatically, noting that his people had lived on this and neighbouring islands for thousands of years. "To be taken away is to lose our deep spiritual connection to the land. This is our home."

The problem of populations uprooted by global warming is generally framed in terms of logistics, geopolitics and economics: who will accomodate them and who will bear the cost?

But there is another dimension that remains largely neglected, said Bina Desai, head of policy and research at the Internal Displacement Monitoring Centre in Geneva.

- Cultural and spiritual home -

"With sea level rise, we have to recognise that there is no return," she told AFP. "It is a resettlement that is not only physical, but cultural and spiritual as well."

For some Pacific islanders, she noted, the thought of leaving without the remains of their ancestors is intolerable.

When people's sense of self is interwoven with the soil and sand, the unique trees and birds of their island homelands, "how can they move without disrupting the identity of their culture?", she asked.

The problem is not unique to island cultures.

"The Saami people belong to Sapmi, and Sapmi belongs to the Saami," said Jannie Staffansson, a member of the Saami Council in Sweden, referring to the cultural region in northern Scandinavia historically inhabited by her people.

Climate change is already devastating the Saami homelands, where snow cover is thinning or melting, and the reindeer upon which so many livelihoods depend are in trouble.

"It is heartbreaking to watch the animals struggle," she told AFP by email. "And it is going to get worse because of other people's unwillingness to change."

"If we lose the reindeer, we lose a huge part of our culture."

On the other side of the Arctic Ocean, things are not much better in Alaska and Canada.

"The Inuit communities want to maintain their way of life," said Dalee Sambo Dorough from the Inuit Circumpolar Council in Canada, which represents some 160,000 indigenous people.

- 'Our people are strong' -

"We depend on the sea ice in the same way that the marine mammals depend on it," she said via Skype. "Hunting is still vital to our culture."

And if things get so difficult that the only option left is to relocate?

"Out of the question -- the Arctic is our homeland," she said.

Yes, she acknowledged, villages already falling into the sea due to crumbling permafrost and storm surges need to be moved.

"But I know that our people are very strong," she said. "We've managed to survive the Arctic by adapting, so we have that capacity."

The Intergovernmental Panel for Climate Change (IPCC) report on oceans and the cryosphere warns of threats to the "cultural identity of Arctic inhabitants," especially indigenous peoples, who number approximately four million.

But these are not the only cultures menaced by global warming and rising seas, noted Anders Levermann, a professor at the Potsdam Institute of Climate Impact Research in Germany and a top expert on Antarctica.

"Hong Kong is currently a beacon of democracy in China, New Orleans is a bastion of culture, and New York too," he told AFP.

"Hamburg, Calcutta and Shanghai -- we are going to lose them all to sea level rise if we do not stop emitting carbon into the atmosphere."