Negotiators from about 200 countries were still poring over draft texts as an unscheduled 13th day of the summit dawned in Glasgow.
Delegates tussled over the fine linguistic points of the deal — from types of concern to whether countries should be urged or requested to take action.
"We have come a long way over the past two weeks and now we need that final injection of that can-do spirit, which is present at this Cop, so we get this shared endeavour over the line," said Britain's Cop26 chief Alok Sharma.
Mr Sharma planned to take soundings after publishing a revised draft of the agreement. He said he hoped for a deal later on Saturday.
“We’ve made very significant progress, but more work needs to be done,” said US climate envoy John Kerry as the UK hosts searched for a breakthrough.
Although the 12-day summit has brought a series of eye-catching announcements, every nation needs to sign off on the final deal that sets out the global response to climate change.
UK Prime Minister Boris Johnson, who is not in Glasgow, weighed in to say that finance for developing countries was key to reaching a deal.
The global south “needs to see the cash on the table” after years of disappointments, Mr Johnson said.
“That’s what needs to happen in the next few hours. People need to see that there’s enough cash to make a start, and there’s enough commitment to make a start,” he said.
Mr Sharma earlier said finance discussions were gathering pace after he bemoaned a lack of progress on a critical part of the talks.
Mr Sharma planned to take further soundings from diplomats before presenting a deal for approval, with delegates preparing to extend their stays in Glasgow.
He said “a small number of key issues remain” which prevented the draft texts presented to delegates from being set in stone.
One of the draft agreements signalled that negotiators had toned down calls to phase out fossil fuels.
It urged countries to turn their backs on “unabated” coal power and “inefficient” subsidies for fossil fuels, adding qualifications to a previous text.
The amendments cast doubt on whether Mr Sharma would succeed in his aim of “consigning coal to history” at Cop26.
He urged negotiators to seize the final hours as a “chance to forge a cleaner, healthier, more prosperous world” and come forward with pragmatic solutions.
“We need that final injection of that can-do spirit which is present at this Cop so we get this shared endeavour over the line,” he said.
After Mr Sharma spoke, dozens of countries took the floor to make their final pleas to the summit, with some lamenting the stalemate over carbon markets — an issue which has remained unresolved since the Paris Agreement in 2015.
Tradable carbon permits are an incentive to use clean energy and can raise money for climate action, but lax rules could let polluters off the hook.
Mattias Frumerie, Sweden’s chief negotiator in Glasgow, told a group of Nordic delegates that more work was needed on the subject in the final hours.
“We’re seeing texts coming out which will probably be revised during the course of the day,” he said.
“There have been some developments which we think are positive but we also want to see further action being taken in these last couple of hours.”
Finance talks have addressed how the rich world will help developing countries to adapt to climate change and develop their economies sustainably.
China indicated it would be willing to support a Cop26 deal but expressed disappointment over a lack of details on how to fund poorer nations.
Changes to the text can include the subtleties of whether countries are urged, requested or invited to take the steps that activists say are essential.
The provisional texts, which may change again before a final version is agreed upon, said rapid CO2 reductions were needed to meet the goals of the Paris Agreement.
The 2015 pact set the goal of limiting global warming to 2° — or preferably to 1.5°C — above pre-industrial levels to prevent impending climate disaster.
The draft agreements in Glasgow called on countries to revisit their 2030 pledges by the end of next year, sooner than required by the Paris deal.
But Leonore Gewessler, Austria’s minister for climate action, revealed there was a group of states who were “lobbying hard for fossil fuel energy".
“The new proposal weakens the coal phase-out. Austria switched off its last coal power station in 2020. And we have to go the same way globally,” she said.
“The 1.5°C goal has to be our north star in climate protection. It is therefore necessary to strengthen it in the final agreement.”
Although some were cheered by the fact fossil fuels were mentioned in the text at all, activists said even the initial version did not go far enough.
“The new final decision text could be better, it should be better, and we have one day left to make it a lot, lot better,” said Jennifer Morgan, the head of Greenpeace International.
“Right now, the fingerprints of fossil fuel interests are still on the text and this is not the breakthrough deal that people hoped for in Glasgow.
“The key line on phasing out coal and fossil fuel subsidies has been critically weakened, but it’s still there and needs to be strengthened again before this summit closes.”
Britain had hailed a breakthrough last week when dozens of countries agreed to phase out coal, which is regarded as the dirtiest fossil fuel.
In another agreement, more than 100 nations promised to cut their emissions of methane, which is highly potent in warming the planet.
The draft text published on Friday “invites parties to consider further actions to reduce by 2030 non-carbon dioxide greenhouse gas emissions, including methane”.
But UN Secretary General Antonio Guterres told delegates that the current suite of national climate plans would actually lead to emissions increasing by 2030.