By Roger Harrabin
Environment analyst, BBC News, Bangkok
Environmentalists fear that a key climate report to be published this week is using outdated science, and will lead to dangerous climate change.
The CO2 safe level row threatens to undermine the IPCC meeting
Campaigners say most of the research for the IPCC's economics report is based on a safe limit of atmospheric CO2 being 550 parts per million (ppm).
But more recent scientific studies now put that figure at 450ppm, they argue.
Attempts by the report's authors to amend the findings to reflect the new data have been resisted by the Chinese.
It is one of many unresolved issues as negotiations at the latest intergovernmental panel on climate change (IPCC) meeting, which is being held in Bangkok, Thailand, draw to a close.
Other big sticking points are over demands from big developing countries that the report makes it crystal clear that rich nations bear responsibility for 75% of the cumulative emissions in the atmosphere.
The draft text of the technical report, which will be used by governments around the world as the basis for national climate policies, concludes that tackling climate change is both achievable and affordable.
But environmental groups say the findings need to be re-evaluated because it is based on the idea that global atmospheric CO2 levels can be stabilised at 550ppm without risking dangerous climate change.
"If governments decided to stabilise at 550ppm, I think we would see dramatic impacts around the world," said Stephanie Tunmore, a Greenpeace spokeswoman.
"Hundreds of millions more people would be at risk from water shortages, and it looks - from recent evidence - as though we would start to lose the massive ice sheets at the poles, resulting in sea level rises."
She added that scientists now warn a safe level of CO2 in the atmosphere is closer to 450ppm - maybe even less.
However, the authors of the economic report are struggling to give priority to the lower stabilisation goals because the majority of economic studies focus on the higher figure.
Attempts to change the emphasis of the report to reflect the new figures have been angrily resisted by Chinese delegates at the conference.
They argue that any change in emphasis would be unsupported by any economic evidence, and would threaten to undermine the nation's drive to tackle poverty.
The current trend of China's emissions would drive global CO2 to much more than 550ppm unless developed nations start making much more radical cuts than they have offered so far.
China is said to be prepared to block any such changes to the report, which is scheduled to be published on Friday.
The Chinese are also negotiating hard to ensure that the document does not imply any necessity for developing nations to tackle climate change.
The original UN agreement, the United National Framework Convention on Climate Change, made it clear that rich nations had to cut emissions first.
China is angry that the US is blaming it for pollution when its per capita emissions are six times higher than China's, yet the Chinese are blamed for the pollution caused while they are manufacturing goods for the rest of the world.
Brazil and India are said to be supportive of the stance adopted by the Chinese on this issue.
But critics of China's hard-line approach point out that the nation will benefit it agrees to be bound by policies like building efficiency proposed by the Bangkok report.