United Nations climate negotiations in Madrid were set to wrap up on Friday with even the best-case outcome likely to fall well short of what science says is needed to avert a future ravaged by global warming.

The COP25 summit comes on the heels of climate-related disasters across the planet, including unprecedented cyclones, deadly droughts and record-setting heatwaves. Scientists have amassed a mountain of evidence pointing to even more dire impacts on the near horizon, while millions of youth activists are holding weekly strikes demanding government action. As pressure inside and outside the talks mounts, old splits between rich polluters and developing nations have re-emerged over who should slash greenhouse gas emissions by how much, and how to pay the trillions needed to live in a climate-addled world. Newer fissures, meanwhile, between poor, climate vulnerable nations and emerging giants such as China and India - the world's No.1 and No.4 emitters - may further stymie progress.

To not lose time, the 12-day meeting was moved at the last minute from original host Chile due to social unrest. But observers and delegates said negotiators had largely failed to live up to the conference's motto: Time for Action. "We are appalled at the state of negotiations," said Carlos Fuller, lead negotiator for the Association of Small Island States (AOSIS), many of whose members face an existential threat due to rising sea levels. "At this stage we are being cornered. We fear having to concede on too many issues that would damage the very integrity of the Paris Agreement."

The narrow aim of the Madrid negotiations is to finalise the rulebook for the 2015 Paris climate accord, which enjoins nations to limit global temperature rises to "well below" two degrees Celsius.

Earth has already warmed 1C, and is on track to heat up another two or three degrees by 2100. But "raising ambition" on emissions remains the overarching goal in Madrid.

Host nation Spain said Thursday that rich and developing nations alike were stalling. "There are two very clear visions," Spain's minister for energy and climate change Teresa Ribera told reporters.

"There are those that want to move quicker and those that want to hide behind things which aren't working, so as not to advance."

The deadline under the Paris treaty for revisiting carbon cutting commitments - known as NDCs, or nationally determined contributions - is 2020, ahead of the next climate summit in Glasgow.

But Madrid was seen as a crucial launch pad where countries could show their good intentions. Nearly 80 countries have said they intend to do more, but they only represent 10 percent of global emissions.

Conspicuously absent are China, India and Brazil, all of whom have indicated they will not follow suit, insisting that first-world emitters step up.

But some countries historically aligned with the emerging giants over the course of the 25-year talks broke rank on Thursday. "The failure of major emitters - including Australia, the United States, Canada, Russia, India, China, Brazil - to commit to submitting revised NDCs suitable for achieving a 1.5C world shows a lack of ambition that also undermines ours," AOSIS said in a statement.

The talks received a meagre shot in the arm Friday after the EU pledged to make the bloc carbon-neutral by 2050. The much-heralded decision was immediately undermined however by the refusal of Poland - a major emitter - to sign on.

Claire O'Neill, Britain's lead delegate in Madrid who will be president of the COP 26 summit next November, told AFP her government would prioritise the climate in 2020 after Prime Minister Boris Johnson's landslide election win.

"The prime minister talked about our legal commitment to CO2 neutrality on the steps of Downing Street last night," she said.

"I report to him and this will be our number one global priority next year." The UN said this month that in order for the world to limit warming to 1.5C, emissions would need to drop over seven percent annually to 2030, requiring nothing less than a restructuring of the global economy. In fact, they are currently rising year-on-year, and have grown four percent since the Paris deal was signed.

"It's basically like what's happening in the real world and in the streets, the protesters, doesn't exist," Alden Meyer from the Union of Concerned Scientists, told AFP. "We are in a fantasy land here." Without strong commitments from big emitters to up their own contributions to the climate fight, Meyer said the talks would have failed to fulfil their purpose.

"Countries need to be on a track to be 1.5C compatible, that's the bottom line."