Divisions that have plagued negotations over a global agreement to limit climate change prompted French Foreign Minister Laurent Fabius to declare a one-day extension to the Paris summit Friday.
After all-night talks between ministers and negotiators hammering out the remaining points from a draft text released late Thursday, Fabius said he remained optimistic that an agreement would be reached by the new Saturday deadline.
"Tomorrow at 9 [0800 GMT], I will be able to present to all the parties a text that, I am sure, will be approved and will be a great step forward for all humanity," Fabius said.
Countries are still divided over how to achieve a long-term goal of keeping global temperature increase to below 2 degrees, with many saying that only a limit of 1.5 degrees will be able to avoid the worst impacts of climate change - including the melting of Arctic and Antarctic ice sheets that contribute to sea levels rising.
The climate agreement is to replace the Kyoto Protocol, which expires in 2020. The United States, which has played a key role in the build-up to the Paris talks, did not ratify Kyoto.
Open-ended questions that remained in the draft text Friday were centred on what has been called "differentiation," which outlines the responsibilities of developed and developing countries. Under Kyoto, only rich countries that had contributed the most to greenhouse gas emissions were required to make major cuts.
Now, many countries are demanding that a new agreement should apply to a broader swathe of nations, including emerging economies.
Who should fund a global transition to renewable energy is another topic of disagreement along with whether everyone should be subject to the same rules on follow-up.
How to define what exactly should happen over the next 85 years has been an issue, with major oil producing countries like Saudi Arabia pushing hard against wording that references fossil fuel phase-outs.
A group of scientists came forward Friday to sound the alarm over the direction of the latest draft agreement, saying that the removal of specific references to time frames and percentages for emissions reductions left the new agreement too vague.