Gruelling negotiations in Poland have added legal flesh to bones of 2015 Paris agreement.

Weary climate negotiators limped across the finish line after days of round-the-clock talks, striking a deal that keeps the world advancing with plans to curb carbon emissions.

But the agreement fell well short of the leap forward scientists - and many of the conference's own participants - say is needed to avoid the cataclysmic impacts of a warming planet.

The deal struck at a global conference in the heart of Polish coal country, where some 25,000 delegates had gathered, adds legal flesh to the bones of the 2015 Paris agreement, setting the rules for how nearly 200 countries cut their production of greenhouse gases and monitor each other's progress.

The agreement also prods countries to step up their ambition in fighting climate change, a recognition of the fact efforts have not gone nearly far enough.

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But like the landmark Paris deal it does not bind countries to hit their targets. And observers asked if that was enough given the extraordinary stakes.

"We are driven by our sense of humanity and commitment to the wellbeing of the Earth that sustains us and those generations that will replace us," said Michał Kurtyka, the Polish environmental official who presided over the two-week summit.

He noted the difficulty of finding global consensus on issues so technical and, in many ways, politically fraught. "Under the circumstances, every single step forward is a big achievement. And through this package, you have made 1000 little steps forward together."

But doubts were aired immediately.

"In the climate emergency we're in, slow success is no success," said Durwood Zaelke, president of the Institute for Governance and Sustainable Development. "In an emergency, if the ambulance doesn't get you to the hospital in time, you die. If the firetruck doesn't get to your house in time, it burns down."

Negotiators said the agreement was the best that could have been expected given the limited agenda for the talks and the need for a global consensus. Virtually every nation was represented at Katowice, ranging from small island countries that threaten to be swallowed by rising seas - and that pushed for a crisis-level response - to the United States, which has said it plans to withdraw from the Paris process.

The US, the world's largest economy and its second-largest polluter, remains in the agreement until at least 2020. It played an at-times contentious role in the negotiations, with its officials rankling fellow delegates by initially refusing to accept a landmark climate report and later putting on a presentation touting the virtues of fossil fuels.

But fellow negotiators said it was mostly notable for its absence. "The US was the driving force in the run-up to Paris. Once they decide to no longer be a part of the agreement, they can't be a driver," said Jochen Flasbarth.

Climate activists march in a protest against global warming in Katowice. Photo / AP
Climate activists march in a protest against global warming in Katowice. Photo / AP

The German said the minimised US role was particularly apparent in negotiations with China, which did not feel as much pressure to ramp up its ambition in fighting climate change as it otherwise might have because the US was not applying it. China is the world's largest producer of greenhouse gases.

This year's conference - an annual United Nations-sponsored exercise now in its 24th year - came against the backdrop of a series of increasingly dire assessments by scientists. In October the UN's Intergovernmental Panel on Climate Change (IPCC) warned that the world was far off-track in its efforts to avoid the most catastrophic effects of warming. It concluded a "rapid and far-reaching" transformation of the world's energy, transport and other sectors will be necessary over the next dozen years to avoid warming the globe more than 1.5C above preindustrial levels.

But rather than lighting a fire under the world to move with more urgency, the report became a source of political friction during the talks in Poland.

Early in the summit, the Trump administration joined Saudi Arabia, Russia and Kuwait in blocking official acceptance of the report's findings.

The clash encapsulated the shift of the US under President Donald Trump.

A chorus of activists and diplomats and national delegates - none more vocal than a coalition of small island states already feeling the impact of rising seas - had implored leaders of the summit to recognise the content of the IPCC report.

The conference was scheduled to end Friday, but repeated deadlines passed, with negotiators haggling through the night and all Saturday.

Negotiators are due to meet in Santiago, Chile, next northern winter.

In between, the UN is hosting a climate summit next September that observers say now takes on crucial importance as a measure of whether countries are serious about upping their ambition.