The talks will attempt to curb emissions caused by burning fossil fuels
The UN's top climate official has given an upbeat assessment on the prospects of a global deal at a climate summit which opens in Copenhagen on Monday.
Yvo de Boer told the BBC things were in "excellent shape" as officials from 192 nations began gathering in Denmark.
Any agreement is intended to supplant the 1997 Kyoto Protocol, aimed at curbing greenhouse gas emissions.
The UN official panel on climate change says emissions must be limited to avoid dangerous global temperature rises.
AT THE SCENE
Richard Black, BBC environment correspondent
There's no doubt that fundamental divisions remain between the various blocs here.
Developing countries are insisting that industrialised nations increase their targets on cutting emissions and put firm pledges of guaranteed money on the table for mitigation and adaptation.
The divide appears very wide but UN officials and some delegates are putting an optimistic slant on things, arguing that the 100-odd heads of state and government due in the for last few days will move far enough to secure some kind of agreement.
"Never in 17 years of climate negotiations have so many different countries made so many pledges. Almost every day now governments are announcing pledges - it's unprecedented," Mr de Boer, executive secretary of the UN climate convention, told the BBC.
"We've got 100 heads of state and government coming to Copenhagen. And, in general, heads of government come to celebrate success, not failure," he said.
Ahead of Monday's talks, the Intergovernmental Panel on Climate Change (IPCC) hit back at claims that human influence on global warming has been exaggerated.
It said it was standing by its findings in response to a row over the reliability of data from a UK university.
Hacked e-mail exchanges from East Anglia's Climatic Research Unit have prompted climate change sceptics to claim that data has been manipulated.
Top Swedish climate official Anders Turesson told the BBC that he hoped the issue "will be investigated".
However, Mr Turesson, who will also be leading EU negotiations as Sweden currently holds the rotating EU presidency, added: "But I cannot see it will in any way affect the negotiations here."
The Copenhagen talks are being held in recognition of the fact that the Kyoto Protocol's targets are not sufficient to avoid impacts projected by the IPCC, and run out in 2012.
Begin 7 December
To discuss emissions targets and financial measures to combat climate change
The US is pledging to cut its emissions in several stages, beginning with a 17% cut from 2005 levels by 2020.
India and China have both agreed to reduce their "carbon intensity", a measure of the amount of carbon dioxide emitted per unit of GDP.
Washington is currently unable to commit to its pledges for the talks, as a bill to cap its emissions is currently stuck in the Senate and will not be passed before the new year.
Australia is in a similar position, after its opposition-controlled Senate rejected a bill to curb emissions.
Mr Turesson said pledges on cutting emissions put forward so far were not enough.
"We have a problem here. First of all it is very welcome that we now indeed have figures from all major players in the climate change negotiations - and that is indeed positive because then we have a basis for discussions.
"But when we sum up here, they do not suffice, so something must be done here in Copenhagen to enhance the pledges."
Sudan's Lumumba Di-Aping, a lead negotiator for the G77/China bloc at the talks, said: "A deal can be done; the science is clear, the economics are clear, the legal issues are clear.
"The question is that some leaders believe their narrow national economic interests take primacy over the existence and well-being of the entire world."
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