The UN chief Antonio Guterres said the announcements in Glasgow are "encouraging, but they are far from enough".
UN chief Antonio Guterres has dubbed climate promises from nations "hollow" while they continue to invest in oil, gas, and coal.
"The announcements here in Glasgow are encouraging, but they are far from enough," Guterres told the COP26 climate summit on Thursday, urging negotiators to "pick up the pace".
"Promises ring hollow when the fossil fuels industry still receives trillions in subsidies."
"We need action if commitments are to pass the credibility test," Guterres said, urging negotiators not to settle for a lowest common denominator outcome.
"We know what must be done."
Representatives from nearly 200 countries have gathered in Glasgow for painstaking talks aimed at keeping the world within the Paris Agreement goal of limiting temperature rise to between 1.5 and 2 degrees Celsius.
But with emissions still rising and current promises putting the world on a path to heat far beyond that target, negotiators were wrangling over a range of issues.
COP26 President Alok Sharma warned that time was running short to clinch a deal before the meeting's scheduled end on Friday evening.
"We still have a monumental challenge ahead of us," he said, appealing to delegates to show more ambition.
Egypt was on Thursday was confirmed as the host of COP27, due for 2022, while the United Arab Emirates will host COP28 in 2023.
READ MORE: COP26: Kicking the can down the road?
The 2015 Paris Agreement saw nations promise to limit heating to "well below" two degrees Celsius and to work towards a safer 1.5C cap through sweeping emissions cuts.
The 1.1C of warming so far is already magnifying weather extremes, subjecting communities across the world to more intense fire and drought, displacement and severe economic hardship.
But the UN says that even the most up-to-date national pledges set Earth on course to warm 2.7C this century.
The issues that remain unresolved at the COP26 include how vulnerable nations are supported financially to green their economies and prepare for future shocks.
Rules over transparency, common reporting of climate action and carbon markets are all also still under discussion.
Also contentious is wording in the draft text to "accelerate the phasing-out of coal and subsidies for fossil fuels", something which large emitters are opposing, according to sources close to the talks.