Ministers launched a last-stretch haggle Thursday for an elusive accord to stave off disastrous global warming, jolted into action by a round of late-night diplomatic sparring between rich and developing nations.
Negotiators are seeking in Paris to crown more than two decades of bruising international diplomacy to reduce humanity's reliance on coal, oil and gas -- fossil fuels which release planet-warming gases.
The 195-nation UN talks in the French capital have been billed as the last chance to avert worst-case-scenario climate change impacts: increasingly severe drought, floods and storms, as well as island-engulfing rising seas.
After nine days of tense negotiations, French Foreign Minister and conference host Laurent Fabius released a draft Wednesday of the final accord to be used as the basis for a frenetic final 48 hours of talks.
"I am convinced we can reach a deal but to do so we must unite our forces and set our compass on the need for compromise," Fabius told the delegates, mostly environment and foreign ministers.
Deep divisions -- primarily between developing and developed nations -- over how to pay for the costly shift to renewable forms of energy, such as solar and wind, have bedevilled the UN climate process.
The new, streamlined text eliminated hundreds of relatively minor points of dispute. Yet all of the main arguments have yet to be resolved.
In a more than three hour-long session on Wednesday night, a host of nations stepped up to voice entrenched positions they warned could derail the effort.
"Many options cross our red lines," Luxembourg negotiator Carole Dieschbourg, representing the European Union, told other delegates.
One of the key battle lines is what cap on global warming to enshrine in the accord, set to take effect in 2020.
Many nations most vulnerable to climate change want to limit warming to no more than 1.5 degrees Celsius (2.5 degrees Fahrenheit) over pre-Industrial Revolution levels.
However several big polluters, such as the United States, China and India, prefer a ceiling of 2C, which would allow them to burn fossil fuels for a while longer.
Barbados's Environment Minister, Denis Lowe, representing a bloc of Caribbean nations among the most vulnerable to rising sea levels, said 1.5C was non-negotiable.
"We will not sign off on an agreement that represents the certain extinction of our people," Lowe said.
For India, the crunch matter is determining a fair division of carbon-curbing responsibility between rich nations, which have polluted for longer, and developing states that need to power vast populations out of poverty.
"A durable agreement cannot be crafted by diluting historical responsibilities or by putting the polluters and the victims at the same level," said Indian Environment Minister Shri Prakash Javadekar.
Rich nations insist that developing giants work harder to tackle their greenhouse gases, noting that much of the world's emissions now come from their fast-growing economies.
Many ministers echoed oft-repeated country positions, but all accepted the draft as a base for further negotiations, scheduled to resume at midnight at a sprawling conference venue in Le Bourget on the northern outskirts of Paris.
Fabius tasked the teams with presenting a final, improved draft on Thursday afternoon -- which would allow for translation into the UN's official languages in time for the deal to be sealed by a deadline of 6pm (1700 GMT) on Friday.
"Now we need to begin to work on compromises," he said.
"This is the decisive moment," French President Francois Hollande said elsewhere in Paris.
"We are not there yet. We are on the track. I hope the good track, but we know there is resistance, questions coming from (various) countries."
One of the biggest potential deal-busters is money.
Rich countries promised in Copenhagen six years ago to muster $100 billion (92 billion euros) a year from 2020 to help developing nations make the costly shift to clean energy, and cope with global warming impacts.
But how the funds will be raised remains unclear -- and developing countries want promises that the amount will be ramped up in future.
Ahead of the Paris summit, most nations submitted voluntary plans to curb greenhouse gas emissions from 2020, a process widely hailed as an important platform for success.
But scientists say that even if the pledges are honoured, they would put Earth on track for warming of at least 2.7C.
One of the remaining battle fronts in Paris is a debate over when and how often to review those national plans, so that they could be "scaled up" with pledges for deeper emissions cuts.
Despite the hurdles, observers say a deal is likely to be reached -- the only question is how high it will aim.
"Our sense is that almost everything we need for an ambitious, equitable agreement is still in play," Jennifer Morgan, global director of the climate programme at the World Resources Institute, told reporters.
"But there is clearly an immense amount of work to be done in the coming hours."