The 10-day conference will be opened by French Foreign Minister Laurent Fabius, who will steer the Paris talks, and Manuel Pulgar-Vidal, Peru’s environment minister, who chaired the last big climate parlay in Lima last December.

Topping the agenda is how to trim a sprawling draft text into something manageable.

At present, the document is an 80-page compendium of national viewpoints, some of which overlap while others are in clear conflict.

The goal is a deal that will save Earth’s climate from potentially catastrophic damage by heat-trapping fossil-fuel gases.

Taking effect from 2020, it would commit the world community to roll back these emissions and help poor countries threatened by worsening drought, flood and rising seas.

But the process remains scarred by memories of the last time the UN tried to forge an ambitious climate deal.

That occasion was in 2009, when a summit in the Danish capital nearly became a fiasco. Leaders jetted in, expecting to bless a new treaty and instead found utter deadlock.

The draft text coalesces around the need to limit warming to a maximum of two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial times.

But beyond this, there are many areas of potential discord.

They include whether to set intermediate goals in emissions reductions and stage regular meetings to press countries to deep their efforts, thus ensuring the planet is kept on the path towards 2 C.

On current emissions trends, say scientists, the planet is on track for possibly 4.8 C of warming this century alone.

So far only 38 UN parties have made pledges to a roster of emissions curbs designed to be the Paris deal’s big brake on carbon.

They include the United States, the European Union, Russia and Canada, but so far not Japan, Australia, Brazil, India or China, the world’s No. 1 emitter.

Despite this, many observers say they are not worried. They expect these major players to make their submissions in the coming weeks or months.

“I think we are finding that a lot of the countries are just finding it’s taking a bit more time than they were going to do originally,” said Liz Gallagher of campaign group E3G.

“It’s not about just one plan, it’s a conversation that’s taking place across governments, across civil society, that says ‘what’s the vision for our country in 2050, what do we want to look like?'”

She added: “For me, that’s a richer conversation to have, and I don’t mind if that delays the process a little bit.”

The G7 summit, taking place in Bavaria on June 7-8, may also have a bearing on the UN talks.

Rich countries are under pressure to explain how they will implement their promise of mustering $100 billion (92 billion euros) a year in climate finance by 2020.