Small island nations, particularly those in the Pacific, are already experiencing "extreme effects" from global warming, and rich nations including Australia have a "moral responsibility" to help them cope with future unavoidable threats, a senior World Bank executive said.

Atoll nations including Kiribati, Tuvalu and the Marshall Islands are seeing shifting rainfall patterns, rising sea-levels and ocean acidification that are forcing islanders to move, said Rachel Kyte, the World Bank's special envoy for climate change.

Kiribati: The island nation is under threat from rising sea levels.

"For some of the islands, we're really talking about the extreme effects of climate change now, which are going to put their entire cultures in jeopardy within the foreseeable future," Ms Kyte said ahead of the biggest gathering of island nation officials for a decade, starting on Monday in Samoa. Foreign Minister Julie Bishop is due to attend.

"We have an obligation to help build these countries' resilience," Ms Kyte said, not only for economic reasons but also for moral ones. "Some will argue that this is an actual issue of justice and an actual issue of rights" given the role rich nations have played in emitting greenhouse gas emissions to "poison" the atmosphere, she said.