Smaller island states will not accept a weak climate pact in Copenhagen that imperils their very existence, an official said.

The 42-member Association of Small Island States (AOSIS) renewed a push on Thursday for a legally binding pact that limits global warming to a maximum of 1.5?C.

"For some countries we are talking about a total sinking," said Solomon Islands envoy Collin Beck, the AOSIS vice chairperson.

"Any higher (than 1.5?C) and we'll have to talk about issues such as relocation, compensation and migration," he said.

Tuvalu, which like the Solomons is a chain of low-lying atolls strung across the Pacific, has exposed a rift among developing nations in Copenhagen by pushing for a new pact that mandates emissions cuts by rich and poor alike.

The AOSIS says the widely held goal of limiting global warming to 2?C compared to pre-industrial times would still expose its members to catastrophic flooding as the oceans rise.

"We've been talking about climate change for 20 years and unfortunately it's taken a crisis to bring it to the world's attention," said Beck.

"But one thing AOSIS will not accept is a weak agreement."