BONN (AFP) - Climate negotiators split on how to fight global warming and who should foot the bill will on Friday (Oct 23) grapple with finalising a draft agreement ahead of a crucial UN summit.

It is the final negotiating day before heads of state and government arrive in the French capital for a Nov 30-Dec 11 conference tasked with sealing the deal.

The pact will be the first to unite all the world's nations in a single arena for reining in global warming and helping vulnerable nations cope with its impacts.

"The most difficult issues remain the same as before," the European Union's top climate negotiator, Elina Bardram, told AFP on Thursday, summing up the first four days of fraught talks in Bonn.

After more than two decades of negotiations, she said, it still boils down to one fundamental disagreement: "How do you divide responsibilities between developed and developing countries?"

A stark reminder came as negotiators bickered when US scientists reported on Thursday that the first nine months of 2015 had been the warmest on record worldwide.

Voluntary national pledges to reduce greenhouse emissions have gone part of the way towards the UN goal of capping warming at two deg C above the mid-19th century benchmark.

But how to fill the remaining "emissions gap" remains highly contentious, with developing countries reluctant to set more ambitious goals unless rich nations provide guarantees of finance.

That money would go towards easing their transition away from cheap and abundant coal to cleaner energy, and for shoring up defences against the impact of climate change.

Money, said negotiators and observers, remains the most obstinate hurdle.

A promise made at a tumultuous 2009 climate summit in Copenhagen to provide US$100 billion (S$139.3 billion) in annual assistance to developing nations from 2020 was devoid of detail.

How much will be for curbing emissions and how much for boosting resilience? Can the money be from grants or loans, or the private sector? All these points remain undefined.

"We shouldn't be waiting for a miracle on finance here," France's climate ambassador Laurence Tubiana said of the Bonn round of talks.

"It is probably a subject that will be dealt with at the end" of the Paris conference, she told journalists on Thursday night.

'SECOND COPENHAGEN' WARNING

The job of negotiators in the former West German capital is to provide a manageable framework for ministers and top leaders to work out political compromises to give the final pact teeth.

Historically, this only happens at the 11th hour of climate conferences, if at all.

For the first time in the history of climate negotiations, the Paris conference will be opened by state leaders, adding to the sense of urgency.

"All parties feel that pressure," Bardram said.

But the Bonn round has left many unsatisfied, with developing countries accusing rich ones of seeking to sweep their core demands off the table, particularly on finance.

As diplomats clashed in a stocktaking session late Thursday, Venezuelan negotiator Claudia Salerno said she had a sense of deja vu.

"I've seen this movie," she told colleagues. "I hope this is not going to be just a really, really nasty, bad second Copenhagen."