PARIS (AFP) - Oscar-winner Robert Redford added star power on Friday (Dec 4) to struggling efforts in Paris to forge an historic pact on global warming, as negotiators battled over a hotly disputed blueprint.

The American actor-turned-environmental campaigner headlined a summit of local leaders from around the world on the sidelines of the United Nations climate conference, aiming to help inject some much-needed momentum into the talks.

"We didn't come to Paris to make history: we came to shape the future. This group is uniquely positioned to do exactly that," said Michael Bloomberg, the co-host of the local leaders' summit.

"We will put local climate action on the global stage. So far, the international negotiations have not recognised the contributions that local leaders can make. We are speaking with one voice, and that voice must be heard."

But at the venue for the 195-nation talks in Le Bourget on the northern outskirts of Paris, negotiators were entrenched in familiar battle-lines over who should shoulder the cost for the effort to tame climate change.

The planned agreement would establish a universal framework for cutting greenhouse gas emissions that trap the Sun's heat, warming Earth's surface and oceans and disrupting its delicate climate system.

Scientists warn Earth will become increasingly hostile for mankind as it warms, such as with rising sea levels that will consume islands and populated coastal areas, as well as catastrophic storms and severe droughts.

However cutting emissions requires a shift away from burning coal, oil and gas for energy, as well the destruction of carbon-storing rainforests - costly exercises that powerful business interests are determined to press on with.

Rich nations have also been reluctant during two decades of UN negotiations to comply with demands from poorer countries that they must pay for the shift to renewable technologies, as well as to cope with climate change.

At stake is hundreds of billions of dollars that would need to start flowing from rich to developing nations from 2020, under the planned Paris pact.

But, with time running out before the talks' scheduled end on Dec 11, the feuding sides had yet to bridge their differences.

South African negotiator Nozipho Mxakato-Diseko, who spoke on behalf of the G77 group of 134 developing and emerging countries, plus China, said on Thursday (Dec 3) night the question of finance was "make or break".

"It has to be clearly understood that finance is critical," she told a news conference.

With frustrations at the conference mounting, UN Secretary-General Ban Ki Moon called on the world's developed economies to honour the financing pledge they made at the last major climate summit six years ago.

"I have been urging the developed world leaders that this must be delivered," Ban told reporters at UN headquarters in New York. "This is one very important promise." On Friday (Dec 4) morning, observers to the talks described them as increasingly hostile.

"The atmosphere at the moment, as I see it, has turned fairly brutal," Kelly Dent, leader of the British charity Oxfam, told reporters on the sidelines.

Another battleground is how much to try and limit global warming.

The biggest polluting nations, such as the United States and China, want to enshrine a target of 2 degrees C above pre-Industrial Revolution levels.

Many weaker nations most at risk want a much tougher target of 1.5 C, which would require the global economy to transform away from fossil fuels and be fully reliant on renewables by 2050.

Lower-level negotiators have until Saturday (Dec 5) to eliminate as many disagreements as possible from a draft text, before handing it over to ministers for them to begin debate on Monday (Dec 7).

Ahmed Djoghlaf, the co-chair of the negotiations, warned Friday (Dec 4) morning of marathon talks to get the job done.

"We intend to be here this morning, we intend to be here this afternoon, we intend to be here this evening and beyond until tomorrow. So we have brought apples for the lunch and the dinner," Djoghlaf told negotiators.

The summit of local leaders in Paris was described as "the largest gathering of global mayors to discuss climate change".

Redford, an Oscar-winning director and long-time environment campaigner, was representing the National Resources Defense Council.

Organisers said he would deliver an address to the event later Friday (Dec 4), and fellow American actor Leonardo DiCaprio was also expected to turn up.

Arnold Schwarzenegger, the action movie star and former governor of California who is also founding head of a non-government organisation helping local governments fight climate change, cancelled his planned attendance, organisers said without offering further details.