Le Bourget - Sleep-starved envoys tasked with staving off catastrophic climate change are on track to seal a historic accord, the French hosts of UN talks said Friday although the biggest pitfalls were yet to be cleared.
The 195-nation conference in Paris had been scheduled to wrap up on Friday, but was extended another day after ministers failed to bridge deep divides during a second consecutive all-night round of negotiations.
Still, Foreign Minister Laurent Fabius, who is presiding over the talks, voiced confidence the event would culminate with a much-awaited pact.
"Things are moving in the right direction," said Fabius, whose optimism was echoed by many negotiators and observers despite potential deal-breakers still up in the air.
World leaders have billed the Paris talks as the last chance to avert disastrous climate change: increasingly severe drought, floods and storms, as well as rising seas that would engulf islands and populated coasts.
The outcome of a laborious two-decade-long process, the post-2020 accord would commit all nations to curb greenhouse gases that trap solar heat, warming Earth's surface and disrupting its delicate climate system.
Highlighting the urgency of the moment, US President Barack Obama and his Chinese counterpart, Xi Jinping, spoke by phone on Friday about the Paris negotiations, according to China's foreign ministry.
Xi said the world powers "must strengthen coordination with all parties" and "make joint efforts to ensure the Paris climate summit reaches an accord", according to a statement on the ministry's website.
The planned accord would seek to revolutionise the world's energy system by cutting back or potentially eliminating the burning of coal, oil and gas, whose carbon dioxide is the big warming culprit.- Battle lines -
UN efforts from the 1990s have been hamstrung by rows between developed and developing nations over sharing the emissions-curbing burden, aiding climate-vulnerable poor countries and funding the shift to cleaner renewables.
Developing nations have insisted established economic powerhouses must shoulder the lion's share of responsibility as they have emitted most of the greenhouse gases since the Industrial Revolution.
But the United States and other rich nations say emerging giants must also do more.
They point out that developing countries now account for most of today's emissions and thus will be largely responsible for future warming.
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The financing issues remained the biggest potential deal-breakers in Paris, highlighted in a draft text presented by Fabius on Thursday that was debated through the night.
Rich countries promised six years ago in Copenhagen to muster $100 billion (92 billion euros) a year from 2020 to help developing nations make the energy shift and cope with the impact of global warming.
But how the pledged funds will be raised remains unclear -- and developing countries are determined to secure a commitment for increasing amounts of money after 2020.
The latest text refers to the $100 billion as a floor, potentially triggering a last-minute backlash from the United States and other developed nations fearful of being forced to sign a blank cheque.
Another remaining flashpoint issue is how to compensate developing nations that will be worst hit by climate change but are least to blame for it.
The developing nations are demanding "loss and damage" provisions, which Washington is particularly wary of as it fears they could make US companies vulnerable to legal challenges for compensation.- Call for compromise -
As he released the draft of the pact, Fabius said a deal was "extremely close" but appealed for compromise from all sides.
Most nations submitted to the UN before the conference their voluntary plans to curb greenhouse gas emissions from 2020, a process that was widely hailed as an important platform for success.
But scientists say that, even if the cuts were fulfilled, they would still put Earth on track for warming of at least 2.7C.
Negotiators remain divided over when and how often to review national plans so that they can be "scaled up" with pledges for deeper emissions cuts.
The draft text sought to end some other key rows, by removing options and giving just one clear proposal on each of the disputes.
One of the most striking was over the temperature limit target to enshrine in the accord.
Nations most vulnerable to climate change had lobbied hard to limit warming to no more than 1.5 degrees Celsius (2.5 degrees Fahrenheit) compared with pre-Industrial Revolution levels.
However several big polluters, such as China and India as well as oil producing-giant Saudi Arabia, prefer a ceiling of 2C, which would allow them to burn fossil fuels for longer.
The latest draft offers a compromise that states the purpose of the agreement is to hold temperatures to well below 2C, but aim for 1.5C.
"With this, I would be able to go home and tell my people that our chance for survival is not lost," said Tony de Brum, foreign minister of the Marshall Islands, one of the archipelagic nations that could be wiped out by rising sea levels.