UN negotiations resume in Geneva on Sunday to streamline the bloated draft for a climate pact that nations, still at odds over key elements, must sign in Paris in December.

The six-day meeting is one of three special sessions added to this year's schedule of talks meant to culminate in the French capital with a historic deal to curb global warming.

On the table is a sprawling 37-page blueprint stuffed with options that reflect conflicting country interests and demands on many fundamental points.

The goal in Geneva will be to trim the document down to a workable draft to be adopted at the close of the talks next Friday as an official "negotiating text" to guide the process through to December.

"This is a critical stage," negotiator Maesela Kekana of South Africa's foreign affairs department told AFP.

"This will be the last opportunity to refine the elements that will inform the negotiation text."

UN climate chief Christiana Figueres said Thursday the February 8-13 talks in Geneva were by no means expected to deliver a polished, finalised draft, but hopefully something that reflects more common ground.

"We're hoping that governments will be able to work with each other for a more manageable text. That is never a guarantee," she told reporters via webcast.

"Of course there is always the possibility that some governments may feel that their views are currently not included and that they would want to include their views. Whether we end up with more pages or less pages still remains to be seen."

The much-touted accord is set to enter into force in 2020 to further the UN goal of limiting global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels.

As part of the process, countries must submit carbon-cutting pledges in the months leading up to the Paris meeting.

- 2014 'hottest year' -

Scientists warn that on current greenhouse gas emission trends, Earth is on track for twice the 2 C target -- a recipe for catastrophic droughts, storms, floods and rising seas.

On Monday, the World Meteorological Organisation said 2014 was the hottest year on record -- part of a "warming trend" set to continue.

Despite the urgency, the UN process remains divided roughly between the interests of rich and developing nations -- as reflected in the unwieldy draft that emerged from the annual ministerial-level talks in Peru last December.

One of the biggest disagreements is centred around demands that rich nations spell out their financial commitments to the developing world for climate mitigation and adaptation actions.

Even the legal form of the agreement itself is in dispute and countries are split on the issue of "differentiation" -- how to divide responsibility for carbon cuts between rich and poor nations.

Procedure requires that an official draft text must be submitted by the end of May this year -- six months before the next Conference of Parties in Paris that will adopt the final version.

"As the Geneva session is the only negotiating session planned before May 2015, its objective is to deliver this negotiating text on 13 February," according to a note by the joint chairmen of the talks.

Observers and parties are hopeful the Geneva meeting will yield signs that the 195 nations gathered under the UN banner are willing to compromise.

"This is going to force parties to really buckle down... to figure out what's important to them to keep, what consolidation or streamlining they can live with and what they can't," said veteran commentator Alden Meyer of the Union of Concerned Scientists.

As the talking continues, many are pointing to the importance of carbon-cutting initiatives by countries, companies and cities outside of the official UN process.

"It would be a fundamental misinterpretation or misunderstanding of the complexity of what we're dealing with to even imagine that an agreement in Paris would in and of itself... miraculously solve climate change," said Figueres.

"What Paris is meant to do is to chart the course that can be followed by governments and by business... toward that two-degree pathway."