In Paris three years ago, countries committed to limit global temperature rises to well below two degrees Celsius (3.6 degrees Fahrenheit), and to the safer cap of 1.5C if at all possible.

But with only a single degree Celsius of warming so far, the world has already seen a crescendo of deadly wildfires, heatwaves and hurricanes made more destructive by rising seas.

Johan Rockstrom, designated director of the Potsdam Institute for Climate Impact Research, said the talks in the Silesian mining city of Katowice were crucial in nailing down how the Paris promises will work in practice.

Delegates at the COP24 talks "cannot and will not discuss if governments worldwide must achieve rapid greenhouse gas emission reductions to limit climate risks -- but how they can do this," he said.

In Katowice, nations must agree to a rulebook palatable to all 183 states who have ratified the Paris deal.

This is far from a given: the dust is still settling from US President Donald Trump's decision to ditch the Paris accord.

G20 leaders on Saturday agreed a final communique after their summit in Buenos Aires, declaring that the Paris Agreement was "irreversible".

But it said the US "reiterates its decision to withdraw" from the landmark accord.

Even solid progress in Katowice on the Paris goals may not be enough to prevent runaway global warming, as a series of major climate reports have outlined.

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