Kiribati president Anote Tong warned people in the region would have to flee in waves similar to the current migrant crisis in Europe unless stronger action was taken to reduce emissions.
"I think it would be incumbent on them because how relevant [would] their presence be," he said.
"We expect them as a our big brothers, not bad brothers, our big brothers to support us on this one."
Australia and New Zealand are the two most economically powerful members of the PIF, which is meeting this week in Port Moresby.