A climate change legal expert advising small island states on how to get an international ruling on their plight says their case is compelling but not clear cut.
Professor Michael Gerrard is among four specialists on a newly formed advisory panel, helping small island states to take a petition to the International Court of Justice in The Hague.
Palau and the Marshall Islands are among those driving the world's first climate change case to be presented to the court.
Climate change law specialist at Columbia University Michael Gerrard says the hope is for a clear declaration that major emitting countries have an obligation to reduce their greenhouse gases.
He says there are clear legal doctrines that one nation may not cause pollution that causes harm across international boundaries.
"But here we have a global issue that the emissions from any one state affect the environment globally. We think that the International Court of Justice should take cognisance of that and should find it to be inappropriate, but we are filing new ground here."
Professor Gerrard says it could take up to two years to get a ruling from the court which could then be used to progress climate change negotiations.