"We're very happy that now at last there is agreement, that all the countries are in agreement that we have a problem with global warming," Tong told Reuters on Thursday during a visit to Tokyo in which he met Prime Minister Shinzo Abe.

"The question is, what can we now do? There's very little we can do about arresting the process," he said.

"We believe it's already reached a stage where it is irreversible for most countries."

Burning fossil fuels releases carbon dioxide and other greenhouse gases into the atmosphere. Scientists say rapidly increasing levels of these gases are warming the planet, causing glaciers to melt and sea levels to rise.

A draft of the UN report projects a big rise in temperatures this century and warns of more sea rises.

Among the nations considered to be at greatest risk is Kiribati, a group of 33 Pacific coral atolls straddling the equator.

Tong said his nation was already suffering, with land and houses washed away and even some public buildings threatened.

But the worst effect was the human toll on Kiribati's 105,000 citizens, he said.

"It's about the lives of the people, the homes, the source of livelihood. A lot of our people survive on taro, and the seawater has gone into that, so it's affecting their lives directly," he said.

Although islanders have tried to move farther away from the water, the narrowness of the low-lying atolls that are their home means that in the end, their only choice may be to leave, perhaps in as little as 50 years, Tong added.

Despite having little to offer economically, Pacific island states such as Kiribati are courted for their support as a bloc in international forums, including by Japan.

At a meeting in the southern Japanese island of Okinawa last year, Japan promised fresh aid of 45 billion yen (US$375 million) to the region over the next three years.

Tong said he was grateful for international support such as this and other efforts to tackle global warming, but feared it was too little and far too late.

"We should have acted a long time ago, and I think that any action that takes place now is dealing with the damage, not stopping the disaster," he said.