Europe's climate commissioner has said world talks must provide a "substantial answer" to global warming in two years to remain relevant, after another United Nations conference gave only modest results.
Even if it succeeded, it was worth reconsidering whether the international conferences needed to be held every year and whether the scope of each session should be narrower, Connie Hedegaard said.
"Maybe it would be time now to think if there should be themes for the conferences so that not each conference is about everything," she said.
The UN talks have failed for 20 years to provide a cure to the world's fever. Heat-trapping carbon emissions that scientists say are warming the planet are growing each year as most countries still depend on coal and oil to fuel their economies.
Besides those emissions, the UN talks deal with a range of complex issues, including monitoring and verification of climate actions, accounting rules and helping developing countries cope with sea level rise, desertification and other affects as they move to clean energy.
The latest two-week session in Warsaw, Poland, nearly collapsed in overtime before agreements were watered down to a point where no country was promising anything concrete.
As the gavel dropped, negotiators emerged with a vague road map on how to prepare for a global climate pact they are supposed to adopt in two years - work Ms Hedegaard says will be crucial in answering whether the world still needs the UN process.
"I think that it has to deliver a substantial answer to climate change in 2015," the Dane said. "If it fails to do so, then I think this critical question will be asked by many more."
Many climate initiatives are happening far from the UN negotiations as governments pursue low-carbon energy sources and energy efficiency. Even international efforts are increasingly taking place outside the UN climate framework.
Governments are working together to slash funding for coal projects, reduce soot and other short-lived climate pollutants and to phase out subsidies for fossil fuels.
China and the US - the world's two biggest carbon polluters - agreed this year to work jointly on energy efficiency, carbon capture technology and other projects.
"This was a missed opportunity to set the world on a path to a global climate deal in 2015, with progress painfully slow," said Mohamed Adow, a climate change adviser at Christian Aid.
"We need a clear plan to fairly divide the global effort of responding to climate change and a timeline of when that will happen."
To avoid the brinksmanship of the UN negotiations, many countries, developed and developing, want to stop the fast rise of potent greenhouse gases called HFCs using another treaty that essentially eliminated the use of ozone-depleting chemicals.
Some observers could not help noting that the Warsaw talks were held in a football stadium where delegates were literally moving in circles.
"It is hard to resist that as a metaphor" for the UN process, said Nathaniel Keohane, vice president of the Environmental Defence Fund and a former special assistant on climate and energy to US president Barack Obama.
The Warsaw talks advanced a programme to reduce deforestation in developing countries but made only marginal progress on building the framework for a deal in Paris in 2015.
Key issues like its legal form and how it will differentiate between the commitments of developed and developing remain unresolved.
"If we go to Paris and say we didn't completely get this done I think ... the world will draw the conclusion you really cannot trust the UN to deliver on this process," said Jake Schmidt, a climate expert at the Natural Resource Defence Council.
UN studies show global emissions need to peak in 2020 and then start falling to stabilise warming at 2C (3.6 F), a level countries hope will avoid the worst consequences of climate change.