Week-long negotiations between scientists from 120 nations are expected to go well into the night here in Bangkok, before the Intergovernmental Panel on Climate Change unveils its findings on Friday.

It will be the third and last of their reports this year, after the first two looked into the evidence and potential impact of global warming, but countries are struggling to find consensus on exactly what should be done.

The economic impacts of reducing greenhouse gases that cause global warming have proved to be the biggest sticking point this week, but other issues such as whether to ramp up use of carbon-clean nuclear power have also caused fierce debate, according to delegates.

"The costs are the big 100,000-pound gorilla in the room," said a source at the closed-door meeting on Thursday.

"The cost is the underlying threat for some and the underlying opportunity for others."

Various delegates contacted by AFP said China has been the leading voice in expressing concern about the costs.

It has sought more than 10 amendments to a draft of the report, saying it will cost more and be harder to reduce greenhouse gas emissions than detailed in the draft, according to documents submitted to the IPCC and seen by AFP.

Carbon dioxide in the atmosphere is measured in parts per million (ppm), with today's levels close to 400 ppm but increasing rapidly.

An early draft of the report seen by AFP says that if the world wants to stabilise carbon dioxide in the atmosphere at 640 ppm by 2030, it would cost 0.2 percent of average global gross domestic product (GDP).

A more ambitious target of 550 ppm, the draft says, would cost 0.6 percent of GDP, and stabilising CO2 in the atmosphere at 445 to 535 ppm by 2030 -- an unlikely scenario -- would be about three percent of GDP.

China has said it does not agree with the estimates, according to documents submitted to the IPCC.

Environmental groups have warned that even at 535 ppm, the world will warm to an extremely dangerous level, causing droughts, floods and other disasters, while at 640 ppm the impacts could be catastrophic.

Traditionally, nations that are in favour of stringent measures to battle climate change want the cost to appear relatively low, while high-polluting nations who want to delay action are keen to portray the price as high.

One delegate from a European nation said that China was trying to water down every single statement relating to the cost of climate change.

"They want the evidence as low as possible on what we know about cost... China is trying to minimise the impact of the comments," the delegate said.

While countries battle it out over a percentage point of GDP, green groups have stressed that it is not only the economic impact nations should consider, but the environmental devastation that climate change brings.

"The costs for ambitious emissions reduction are very low compared to the dangers caused by climate change if they take no action," said Stephan Singer, European head of climate and energy policy at environmental group WWF

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