COP26 President Alok Sharma said there was still an array of unfinished business at the crunch UN climate summit on Thursday as scientists urged negotiators to heed their warnings for the need for urgent action to global warming.
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 - from slashing greenhouse gases to financial help for countries already facing supercharged storms, floods and droughts.
"We are not there yet. There is still a lot more work to be done," Sharma told delegates on Thursday, adding he was "concerned" particularly at the number of finance issues still unresolved a day before the meeting is due to wrap up.
"The world is watching us and they are willing us to work together and reach consensus. And we know that we cannot afford to fail them."
His comments come in the wake of a joint China-US pact to accelerate climate action this decade, that experts said should allay fears that tensions visible early in the summit might derail the talks.
The surprise declaration, unveiled by envoys John Kerry and Xie Zhenhua, said the world's two largest emitters "recognise the seriousness and urgency of the climate crisis", although it was light on detailed action.
Importantly, the document stressed the need for carbon pollution to fall this decade and committed to work swiftly to reduce their emissions of methane - a potent greenhouse gas.
"It can only be good news that the US and China are working closely on climate change and slashing methane emissions," said Bernice Lee, research director at the Chatham House think tank.
"But the statement is not enough to close the deal. The real test of Washington and Beijing is how hard they push for a 1.5C aligned deal here in Glasgow."
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.
Countries also agreed to redouble their emissions cutting plans every five years under the agreement's "ratchet" mechanism designed to produce ever-growing climate ambition.
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.
And the UN says that even the most up-to-date national pledges set Earth on course to warm 2.7C this century.
To keep from overshooting the 1.5C target the Intergovernmental Panel on Climate Change says emissions must fall 45 percent this decade.
More than 200 scientists sent an open letter to the COP26 summit Thursday urging countries to take "immediate, strong, rapid, sustained and large-scale actions" to halt global warming.
"Cumulative greenhouse gas emissions to date already commit our planet to key changes of the climate system affecting human society and marine and terrestrial ecosystems, some of which are irreversible for generations to come," said the letter.
Wednesday saw the release of draft "decisions", which were the first real indication of where nations are 10 days into deeply technical discussions.
The text, which is sure to change during ministerial debates, called for nations to "revisit and strengthen" their new climate plans, known as nationally determined contributions (NDCs) by next year, instead of 2025 as previously agreed.
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.
And nations already hit by climate disasters are demanding "loss and damage" support from rich emitters.
But the main sticking point is ambition: which countries plan to slash their carbon emissions fast enough to avert dangerous heating.
European Commission vice president Frans Timmermans said that the US-China pact would have a "positive influence" on discussions in Glasgow.
"With all the difficulties they have on other issues, to now actually signal this issue transcends other issues ... that helps the global community come to terms with the fact that we have to act now," he told AFP.