LE BOURGET (AFP) -- Negotiators tasked with saving Earth's climate system embarked Tuesday on an 11-day race to overcome decades-long disputes as experts pointed to a towering threat from coal.

A day after world leaders pledged to tame global warming, bureaucrats from 195 nations scrambled to shape a labyrinthine 54-page text into a blueprint that can be approved by December 11.

The goal -- endorsed ringingly by around 150 heads of state and government at the start of the talks on Monday -- is to commit every nation to a post-2020 pact to roll back emissions of carbon gases.

Scientists have long warned that time is short for weaning humanity off its dependence on burning fossil fuels, the backbone of the world's energy supply and biggest source of these heat-trapping emissions.

But, heaping pressure on negotiators, researchers for the respected group Climate Action Tracker said Tuesday the clock was now ticking even faster than before.

If planned new coal-fired plants come online, they said, the added emissions would wreck hopes of meeting the UN target of curbing warming to two degrees Celsius (3.6 degrees Fahrenheit) from pre-Industrial Revolution levels.

"There is a solution to this issue of too many coal plants on the books:  cancel them," said Pieter Van Breevoort of Ecofys, an energy research organisation which is part of Climate Action Tracker.

"Renewable energy and stricter pollution standards are making coal plants obsolete around the world, and the earlier a coal plant is taken out of the planning process, the less it will cost."

The talks, taking place a heavily secured conference centre at Le Bourget on the northern outskirts of Paris, headed into the detail phase after the verbal flourishes of Monday, when around 150 leaders gathered for the biggest one-day summit in UN history. 

Threat for small islands

"Never have the stakes of an international meeting been so high, because it concerns the future of the planet, the future of life," French President Francois Hollande said in an opening speech.

"The hope of all of humanity rests on all of your shoulders."

US President Barack Obama on Tuesday met with the heads of small-island states, who are among the nations most at threat from climate change.

"Some of their nations could disappear entirely and as weather patterns change," said Obama.

"We might deal with tens of millions of climate refugees in the Asia Pacific region."

Obama added: "These nations are not the most populous nations, they don't have big armies (...) but they have a right to dignity and sense of place."

"Their voice is vital in making sure that the climate agreement that emerges here in Paris in not just serving the interest of the most powerful."

More than two decades of UN climate negotiations have left veteran observers skeptical about the kind of high-flown rhetoric heard from the podium on Monday.

Climate diplomacy touches the live wire of national interests, among users and sellers of fossil fuels, especially among countries keen to use cheap and plentiful energy to power their growth.

Rifts

Divisions quickly emerged in Paris on Monday, as leaders of developing nations hit out at rich countries for perceived hypocrisy in making demands to use fewer fossil fuels after carbon-burning their way to prosperity.

"The prosperous still have a strong carbon footprint and the world's billions at the bottom of the development ladder are seeking space to grow," said Indian Prime Minister Narendra Modi, who refuses to commit his country to abandon its coal resources to power economic development.

Modi argues his nation is doing all it can to move to cleaner energy sources, however.

In Paris, he launched an alliance of 121 sun-drenched countries, rich and poor, to dramatically boost the use of solar power.

The group vows to mobilise more than $1 trillion in investment by 2030 for the "massive deployment" of affordable solar power.

In an effort to bridge the diplomatic divide between rich and poor, which have dogged the annual climate parlays, Hollande promised Tuesday two billion euros in the next four years to help Africa move towards clean energy sources.

Many nations appeared to show greater determination to forge a climate accord as a sign of solidarity with France after the November 13 terror attacks, claimed by Islamic State jihadists, which killed 130  people in Paris.

French police banned demonstrations on Paris' prestigious Champs Elysees avenue and near the conference venue at Le Bourget north of the capital for the duration of the two-week UN climate talks.