Major economies have resisted calls for bolder commitments as a UN summit in Madrid has limped towards a delayed conclusion, dimming hopes that nations would act in time to mitigate the impacts of climate change.

Key points: The summit was due to end Friday but dragged on with disputes over implementing the Paris deal

The summit was due to end Friday but dragged on with disputes over implementing the Paris deal The Paris agreement enters a crucial implementation phase in 2020

The Paris agreement enters a crucial implementation phase in 2020 The EU's 28 member states, bar Poland, agreed to target net zero emissions by 2050

World leaders have been tasked with setting new emissions reduction benchmarks at COP25 in Madrid — the 25th meeting of the Conference of the Parties to the United Nations Convention on Climate Change — but many nations slammed Chile, presiding over the talks, for drafting a summit text that they said risked throwing the 2015 Paris Agreement to tackle global warming into reverse.

The Paris Agreement came into force in November 2016 and calls on signatories to drastically reduce emissions to a limit global temperature rise to no more than 1.5 degrees Celsius before 2100.

It also called on wealthier nations to provide developing countries with financial aid to assist their transitions to cleaner economies.

The annual UN climate summit had been due to conclude on Friday but dragged on with delegates mired in multiple disputes over implementing the Paris deal, which has so far failed to stem the upward march of global carbon emissions.

The leaders are yet to agree on several issues including targets for cutting greenhouse gas emissions, financial aid for countries most at risk and rules on carbon trading.

Long-time participants in the talks were outraged at the unwillingness of major polluters, including Australia, to show more ambition with plans to tackle the climate crisis, after a year of wildfires, cyclones, droughts and floods.

'Our window of escape is getting harder and harder'

Rising sea levels are already forcing displacement among some vulnerable Pacific coastal communities. ( Brad Marsellos: ABC Open )

Current national climate plans, if achieved, would lead to a temperature rise of at least 3 degrees, a level of warming that scientists say could lead to widespread food and water scarcity, more weather disasters and rising seas.

The science and growing public demand for action is heaping pressure on governments to meet a deadline to strengthen their climate plans by the end of next year — but only about 80 smaller-emitting countries have so far said they will.

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The European Union, small island states and many other nations had been calling for the Madrid decision to signal that the more than 190 countries participating in the Paris process will submit more ambitious pledges to cut emissions next year.

Carlos Fuller, chief negotiator for the Alliance of Small Island States, said the 44 low-lying nations in the bloc wanted strict rules but were being sidelined as larger countries dominated the talks.

"Are we a party to this process or not?" Mr Fuller asked reporters outside a meeting hall.

This was echoed by Papua New Guinea's climate envoy Kevin Conrad, who told reporters "90 per cent" of COP25's participants had not been involved.

The agreement enters a crucial implementation phase in 2020 when countries are supposed to ratchet up their ambitions ahead of the next major round of talks in Glasgow.

If big polluters such as Australia, China, India, Japan, Brazil and others fail to agree to more meaningful climate action soon, then scientists say already slim hopes of averting catastrophic temperature rises will all but vanish.

Alden Meyer, director of strategy and policy for the Union of Concerned Scientists, said he had attended the climate negotiations since they first started in 1991.

"But never have I seen the almost total disconnect we've seen here at COP25 in Madrid between what the science requires and the people of the world demand, and what the climate negotiations are delivering in terms of meaningful action," he said.

"The planet is on fire and our window of escape is getting harder and harder to reach the longer we wait to act."

'A quantum leap in the other direction'

There was anger among campaigners directed at Chile, which is presiding over the summit. ( Reuters: Javier Barbancho )

Although no advanced economy is yet on track for the kind of action scientists say is needed to steer the climate onto a safer path, all the EU's 28 member states, bar Poland, agreed in Brussels on Thursday to target net-zero emissions by 2050.

Krista Mikkonen, Finland's Environment Minister, speaking on behalf of the EU, told the talks that it would be "impossible to leave" without agreeing a "strong message" on the need to redouble pledges to cut emissions next year.

Tina Steger, climate envoy of the Marshall Islands, echoed the call, telling delegates: "It appears we are going backwards on the issue of ambition when in fact we should be calling for a quantum leap in the other direction."

Ministers broke into groups on Saturday (local time) for eleventh-hour negotiations on a tangle of issues, including finance for climate-vulnerable countries, carbon markets, and the all-important issue of the strength of the summit's final text.

The Paris process has been weakened by a move by US President Donald Trump to begin withdrawing the world's largest historical emitter from the agreement last month, making it easier for other big countries to backslide.

Chile became the target of anger among campaigners, who said the draft text circulating was among the worst they had seen in many years of UN climate negotiations.

Outside the talks, supporters of the international group Extinction Rebellion stood on 12 blocks of ice with nooses around their necks to symbolise the disappearing time left to "change the trajectory and truly face the reality of the planetary climate and ecological emergency", the group said.

Extinction Rebellion protesters warned of the "planetary climate and ecological emergency" in Madrid. ( AP: Manu Fernandez )

"At a time when scientists are queuing up to warn about terrifying consequences if emissions keep rising, and school children are taking to the streets in their millions, what we have here in Madrid is a betrayal of people across the world," said Mohamed Adow, director of Power Shift Africa, a climate and energy think tank in Nairobi.

"The approach Chile has taken on this text shows how it has listened to the polluters and not to the people," said Jennifer Morgan, executive director of Greenpeace International.

In response to critics, Andres Landerretche, coordinator of the summit for Chile, said they would aim "at a more ambitious text".

"We are at a defining moment and we need to have an outcome based on what the science is telling us," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 44 seconds 44 s The UN has warned that humanity is running out of time to save itself from climate change.

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