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.
Nevertheless, various delegates contacted by AFP said an agreement was still expected to be reached in the early hours Friday.
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 solar, wind, 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.
One top priority is how to cut the levels of carbon dioxide in the atmosphere, which are measured in parts per million (ppm). Today’s levels are close to 400 ppm.
An early draft of the report seen by AFP says that if the world wants to stabilise carbon dioxide levels at 640 ppm by 2030, it would cost 0.2 percent of average global gross domestic product (GDP) in that year.
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.
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.
And although the United States has maintained a relatively low profile at this week’s talks while China has come under the spotlight, WWF said the world’s superpower was most to blame for global warming.
"They are the biggest culprit and they are the biggest offender of climate," said Singer.
A longtime advocate for the environment, Gore presents a wide array of facts and information in a thoughtful and compelling way. “Al Gore strips his presentations of politics, laying out the facts for the audience to draw their own conclusions in a charming, funny and engaging style, and by the end has everyone on the edge of their seats, gripped by his haunting message,” said Guggenheim.