The UN estimated on Tuesday that nations' carbon-cutting pledges imply a far-from-sufficient 10-percent emissions cut by 2035, cautioning that it was unable to provide a robust global overview after most countries failed to submit their plans on time.

With just days to go before tense COP30 climate talks in Brazil, UN Climate Change provided an emissions calculation alongside its formal assessment of national 2035 pledges.

The extra calculation incorporated elements from countries and regions such as China and the European Union.

UN secretary-general Antonio Guterres said last week that slow action from nations meant it was "inevitable" that efforts to limit temperature rise to 1.5 degrees Celsius would fail in the short term, unleashing devastating impacts during a period of overshoot as countries worked to pull temperatures back down again by the end of the century.

UN climate chief Simon Stiell said the estimated 10-percent emissions cut suggested that "humanity is now clearly bending the emissions curve downwards for the first time, although still not nearly fast enough".

The UN's Intergovernmental Panel on Climate Change has said emissions must fall 60 percent by 2035, from 2019 levels, for a good chance of limiting global warming to 1.5 degrees above pre-industrial levels – the more ambitious goal of the Paris climate deal.

"The science is equally clear that temperatures absolutely can and must be brought back down to 1.5 degrees as quickly as possible after any temporary overshoot, by substantially stepping up the pace on all fronts," Stiell said in a statement.

The two-week COP30 climate negotiations in the Amazon, which start on November 10, are tasked with galvanising momentum in the face of a hostile United States, geopolitical tensions, economic concerns and fears that the most ambitious climate targets are already slipping out of reach.

The 2015 Paris climate accords aimed to limit global warming to well below two degrees above pre-industrial (1850-1900) levels – and 1.5 degrees if possible.

With average warming already around 1.4 degree today, many scientists believe that the 1.5 degree threshold will likely be breached before the end of this decade as humans continue to burn oil, gas, and coal.

But they stress that each fraction of a degree of temperature increase avoided is crucial to limit the danger.

If temperatures overshoot 1.5 degrees, experts say humanity would likely have to try to pull warming back down by using technologies to remove carbon from the atmosphere that are not yet operational at scale. (AFP)