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, but other issues such as whether to ramp up use of nuclear power have also caused fierce debate, delegates said.

"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."

The final report is likely to say that world leaders have little time to waste, but that the tools for reducing greenhouse gas emissions already exist.

A draft summary of the IPCC report seen by AFP calls for a greater use of renewable energies such as biofuels and hydro-power, as well as ways to use energy more efficiently.

Storing carbon dioxide, the biggest greenhouse gas, underground is also under consideration, as are tariffs and other economic mechanisms to make using fossil fuels more expensive and renewable energies much cheaper.

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

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

"They want the evidence to appear as weak as possible on what we know about cost," one delegate from a European nation said.

Carbon dioxide in the atmosphere is measured in parts per million (ppm), with today's levels close to 400 ppm and 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, which relies heavily on cheap coal to fuel its booming economy, has said in documents submitted to the IPCC that it does not agree with the economic cost estimates.

Environmental groups warn 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.

Renaud Crassous, one of the French delegates, said that nuclear power provoked a lengthy debate on Wednesday.

"Some countries are fiercely against nuclear and they were not comfortable with the fact that it will figure (in the IPCC report) among the other options for mitigating climate change," he told AFP.

While countries battle it out over the economic costs, green groups have stressed that the looming environmental devastation should be the top priority.

"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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