Negotiators from around 190 countries are meeting in Warsaw to try to advance steps towards a global climate agreement.
Participants say there is a growing sense of realism about the scale of what can be achieved in any new deal.
But there are concerns that the process could become bogged down in procedural wrangling after Russia asked for a review of voting procedures.
The meeting comes amid new warnings about global levels of warming gases.
This will be the 19th annual Conference of the Parties (COP) to the UN Framework Convention on Climate Change (UNFCCC).
At the meeting in South Africa in 2011, delegates adopted what's termed the Durban Platform which stated that a new international agreement should be negotiated by 2015 and come into force by 2020.
Now in Poland, negotiators are coming to terms with the emerging shape of that deal.
"There is a fair degree of convergence emerging about the character of a new agreement," said Elliot Diringer from the Centre for Energy and Climate Solutions, a long-time observer of the negotiations.
"This reflects a greater sense of realism among the parties about what can accomplished in this process."
The delegates have been scarred by the experience in Copenhagen in 2009, when ambitions for a comprehensive deal foundered, despite the intense efforts of President Obama, Prime Minister Gordon Brown and others.
What's emerging now is a looser agreement whereby countries set their own targets, but are subject to some form of review by other nations.
"The sort of model that's emerging for Paris, this acceptance of the notion that commitments will be self defined, it's a recognition that where the rubber really meets the road is at the domestic level, and the agreement needs to reflect that," said Elliot Diringer.
The meeting comes after a series of studies indicating the scale of the climate challenge. The fifth assessment report from the IPCC published in September suggested that without concerted political action the accepted 2C threshold to dangerous climate change would be passed sometime in the middle of this century.
Just this week the World Meteorological Organization reported that concentrations of greenhouse gases in the atmosphere were higher than ever. While the UN Environment Programme detailed the yawning gap between what nations have pledged to do and where the world needs to be in 2020 to avoid the worst impacts.
According to the UNFCCC executive secretary Christiana Figueres, Warsaw is a pivotal moment to advance momentum towards a deal.
"We still have time and the means to limit warming to 2 degrees C. And the international process must push forward now to build the foundation for an ambitious universal climate agreement in 2015," she said.
But there are a number of difficulties on the road to Paris where the 2015 meeting will be held.
Russia has emerged as a potential problem for the process as they have tabled an amendment on decision-making at the COP.
The process works on the basis of consensus but the Russians believe their objections were overruled at the meeting in Doha last year.
"Decision-making in the UNFCCC process has suffered evident setbacks over the past few years," the Russian delegation wrote in a statement.
It goes on to state that the voting system within the meeting needs to be addressed to rebuild confidence.
Climate cliff hanger
The Russian concerns led to stalemate at a sub-meeting in June. There are worries that this might continue to hamper progress in Warsaw, where delegates will be keener than ever to avoid a breakdown.
"This has been haunting the process even before the Russians brought it up," said Norine Kennedy, who will be representing US business at the meeting.
"We've had a succession of COP cliff hangers and one or two countries always get rolled over in the effort to find consensus and last year that was Russia.
"The consensus question will have to be faced sooner or later and it's better they do this now than in Paris," she said.
Another key question is the shifting nature of development. Where once the UNFCCC was neatly divided into developing and developed nations, with the richer ones making all the cuts in emissions, there is now a greater push for every country to bear some of the load.
But not everyone is keen on this.
"I saw some comments from the Chinese side, saying they are going to insist on a common but differentiated responsibilities point, said Norine Kennedy.
"That will be a hard fought fight and it will lurk behind most of the interventions we will hear over the next couple of weeks."
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