SYDNEY - Adapting to a sea level rise of up to 0.5 meters will cost the three most vulnerable Pacific atoll nations nearly $10 billion - equivalent to about 20 years of gross domestic product - the World Bank said in a report on Thursday.

Kiribati, Tuvalu and Marshall Islands are among the smallest, most remote and dispersed countries in the world, spread across 6.4 million square kilometers of Pacific Ocean, where residents live at an elevation of no more than 2-3 meters, the report said.

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A third of the population of Kiribati and Tuvalu are at risk of falling into extreme poverty from climate shocks such as coastal flooding, while healthcare is under pressure from increased heat-related illness, it said.

A sea level rise of 0.5 meters, which would submerge significant portions of these nations, could occur as soon as 2050 under a worst case scenario, or more likely by 2070, and it was imperative for governments to act on adaptation plans now, it said.

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Money is a central focus of the COP29 climate talks being held in Azerbaijan and the success of the summit is likely to be judged on whether nations can agree a new target for how much richer nations, development lenders and the private sector must provide each year to developing countries to finance climate action.

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The Pacific atolls face a significant climate funding gap, the World Bank report said.

Importing sand and rock to build sea walls and raise and reclaim shorelines will also be costly and challenging, it added.