In an exclusive interview on Thursday with the Associated Press, Guterres said the negotiations in Glasgow, Scotland – set to end on Friday – will “very probably” not yield the emissions-cutting pledges he has said are needed to keep the planet from warming beyond the 1.5C threshold.

So far, the talks have not come close to achieving any of the UN’s three announced priorities for the annual conference called COP26.

One is cutting carbon dioxide emissions by about half by 2030 to reach the goal Guterres alluded to.

The other two are getting rich countries to fulfil a 12-year-old pledge of providing $US100 billion ($A137 billion) a year in financial climate aid to poor countries and ensuring that half of that amount goes to helping developing countries adapt to the worst effects of climate change.

Guterres said the Glasgow talks “are in a crucial moment” and need to accomplish more than securing a weak deal that participating countries agree to support.

“The worst thing would be to reach an agreement at all costs by a minimum common denominator that would not respond to the huge challenges we face,” Guterres said.

That’s because the overarching goal of limiting warming since pre-industrial times to 1.5C by the end of the century “is still on reach but on life support,” Guterres said.

The world has already warmed 1.1C, leaving far less than a degree before the threshold is hit.

Less than 36 hours from the scheduled close of the negotiations, Guterres said that if negotiators can’t reach ambitious CO2-cutting goals – “and very probably it will not happen” – then leaders of countries would need to come up with new pledges next year and in 2023 during high-level meetings.

He said it is “very important” that countries update their goals and send top leaders to the climate talks every year, at this point.

However, Guterres would not say at what point he thinks the 1.5C goal would have to be abandoned.

“When you are on the verge of the abyss, it’s not important to discuss what will be your fourth or fifth step,” Guterres said.

“What’s important to discuss is what will be your first step. Because if your first step is the wrong step, you will not have the chance to do a search to make a second or third one.”

Guterres praised a Wednesday evening agreement between the United States and China to cut emissions this decade as a reason why he still hopes for some semblance of success in Glasgow.

He said China promising that its CO2 emissions would peak by 2030 represented a key change in the top emitter’s outlook.

The UN chief said he hoped that two sticky issues that defied resolution for six years can be solved in Glasgow: creating workable markets for trading carbon credits and transparency that shows that promised CO2-reducing actions are real.

“It is the moment to reach agreement by increasing ambition in all areas: mitigation, adaptation and finance in a balanced way,” Guterres said.

UK Prime Minister Boris Johnson on Wednesday urged fellow world leaders to call their negotiating teams in Glasgow and give them the political backing to clinch an ambitious deal.

Officials and observers have said the bar for success must be a strong affirmation of the goal set in Paris in 2015 of keeping global warming well below 2C – ideally no more than 1.5C – backed by credible policies from all countries to get there.