In an interview with AFP in Geneva, Heine detailed a range of projects underway aimed at helping prepare and adapt her far-flung country, made up of 1,156 low-lying islands, scattered over 29 coral atolls, to rapidly shifting realities brought on by climate change.

"We have to do something, because the only other option is to sit there and wait for the water to come," she said.

Most of the Marshall Islands lie less than two metres (6.5 feet) above sea level, leaving the Pacific Ocean archipelago's some 55,000 inhabitants "sitting ducks when it comes to sea level rise," she said.

The Marshall Islands is among the countries most immediately threatened by unchecked climate change.

Heine lamented that many countries were not taking the threat against small island states seriously enough. She described Washington's decision to withdraw from the Paris climate accords as "deeply disappointing".

Faced with lacklustre efforts to slow warning, she said the Marshall Islands' "survival depends on innovative approaches", pointing for instance to ongoing discussions about possibly elevating some of the islands.

"In order for the Marshall Islands as a country and as a culture and as a people... to remain in the future, we need to make sure we have higher grounds," she said.

Heine said the project, which is part of a national climate change adaptation plan due to be published next year, would obviously "cost a lot of money".

The Marshall Islands has been lobbying the World Bank, the Green Climate Fund and others for a special designation for atoll nations that would give them easier access to grants and loans for climate adaptation projects.

The country itself is spending more to address the negative consequences of climate change already being felt and to prepare for future shifts, including through the building of sea walls around island communities.

The share of its gross domestic product dedicated to disaster risk management and preparedness has doubled from five to 10 percent over the past four years alone, Heine said.

- 'Disaster' -

But this may not be enough. The Marshall Islands is also preparing for the possibility that the territory could eventually be swallowed by the sea.

"We want to stay where we are, where we belong, but if it comes to that then we need to consider... strategies," Heine said.

She pointed out that Marshall Islanders are granted visa-free travel to the United States, and many have already gone there to start fresh.

"If it looks like we won't be able to save the Marshall Islands, than perhaps more people will take that option," she said, adding that she would "hate to see that because that means the disappearance of the Marshall Islands as a country".

"That to me would be a disaster."

The country is also considering petitioning the UN to ensure that "borders can continue to remain where they are even though they are submerged under water".

"Even if people relocate elsewhere, their ownership of a certain piece of the ocean would remain," ensuring rights to fishing and other marine resources, she said.

"I think some kind of discussion along that line needs to start taking place," she said.

- Nuclear 'leakage' -

At the same time, rising sea levels could also exacerbate the threat left by the Marshall Islands' nuclear legacy.

The US, which detonated 67 bombs at the Enewetak and Bikini atolls between 1947 and 1958 as part of its nuclear test programme, built a dome-shaped structure on Runit island to store the radioactive debris.

Rising seas are now threatening to undermine the structural integrity of the thick concrete dome, which has already developed cracks.

The US energy department insists there is no danger, but the Marshall Islands wants the UN or another country to "help with an independent assessment of the leakage," Heine said.

"How can it be safe?"