But it says there is a wide variety of technology already available to fight climate change at costs bearable by much of the developing world responsible for a lot of the current growth.
They include as nuclear, solar and wind power, more energy-efficient buildings and lighting. Capturing and storing carbon dioxide spewed from coal-fired power stations and oil and gas rigs is also feasible.
In some cases, such technologies could lead to substantial benefits, such as cutting health costs by tackling pollution.
Even changing planting times for rice paddies or managing cattle and sheep flocks better could cut emissions of methane, another powerful greenhouse gas, it says.
The report is the third to be released this year by the UN panel, which draws on the work of 2,500 scientists.
The previous two painted a grim future of human-induced global warming causing more hunger, droughts, heatwaves and rising sea levels which would drown low-lying islands.
In Bangkok, China and Europe sparred about the costs and levels of greenhouse gas emissions which ought to be allowed. Delegates also debated the role of nuclear power.
China, the world’s number two emitter of greenhouse gases after the United States, wanted the IPCC report to exclude language which would promote stabilising emissions near current levels in part because of the limited economic studies available.
The report says the steeper the emissions cuts, the more costly to the global economy.
The amended draft says that in 2030 the costs for mitigating greenhouse gases at stabilisation levels of 445 and 710 ppm CO2-equivalent are estimated at between a 3 per cent decrease of global GDP and a small increase.
But it says regional costs might differ significantly from global averages.
The senior delegate said focusing on 445 ppm (parts per million) was unrealistic given the rapid growth in emissions, particularly from the developing world.
The European Union wants the lowest level possible to achieve its goal of a maximum two degrees Celsius rise in global temperatures, a level it says is a threshold for ”dangerous” changes to the climate system.
Greenhouse gas concentrations are now at about 430 ppm CO2-equivalent.
A UN official said approval was expected within a few hours.
”The text has been agreed but formal approval is at 10 am,” said meeting spokeswoman Carola Traverso Saibante, referring to the 0300 GMT time when delegates were due to reconvene to endorse the report.
The talks between scientists and government officials from more than 100 countries ran into the early hours of Friday to try to resolve complex issues raised in the report by the Intergovernmental Panel on Climate Change (IPCC).
The final issue to be decided centred on the meaning of the word ”uncertainty” in one of the report’s annexes, said a delegate who did not want to be named.
China and Europe sparred over the costs and levels of greenhouse gas emissions. Delegates also debated the role of nuclear power.
China, the world’s number two emitter of greenhouse gases after the United States, wanted the IPCC report to exclude wording about scenarios for stabilising gas levels near current levels.