Children born today will be fighting each other for food and water in 2050 if the Cop26 climate summit fails, exhausted delegates were told as negotiators fight over the final details of a potential deal.

The deadline for the fortnight-long talks to finish came and went as leading figures took to the floor for what they hoped would be the final time, to exhort each other to cooperate in the interests of people threatened by the climate crisis around the world.

At stake is the world’s chance of holding global heating to 1.5C above pre-industrial levels, the tougher of the two temperature goals in the 2015 Paris climate agreement and a “planetary boundary” beyond which the ravages of climate breakdown will rapidly become catastrophic and irreversible.

Cop26 president Alok Sharma said a new draft would be published early on Saturday, after which it would be debated. Sharma said he anticipated the summit would finish on Saturday afternoon.

EU vice-president Frans Timmermans said: “If we fail [my one-year-old grandson] will fight with other human beings for water and food. That’s the stark reality we face. So 1.5C is about avoiding a future for our children and grandchildren that is unliveable.”

John Kerry, the US climate envoy, said: “We believe this is existential and, for many of you, existential today. People are dying today.”

The head of delegation from Tuvalu, a Pacific island nation, was rousingly cheered when he warned that his country was sinking beneath the waves. Kenya’s representative warned that heating of 1.5C on average around the world was likely to equate to 3C in many parts of Africa, a rise that would cause frequent heatwaves and devastating drought.

Earlier on Friday, the UK as host nation of the talks circulated a second draft text for the outcome. This included a resolution for countries to start to phase out “unabated” coal power and “inefficient” fossil fuel subsidies, and a request for countries to return to the negotiating table next year to strengthen their national plans on cutting greenhouse gas emissions.

Whether and how countries will revise those national plans – known as nationally determined contributions (NDCs) – is now at the heart of the talks. Research earlier this week by the Climate Action Tracker, an analyst organisation, found that current NDCs presented by countries in Glasgow would lead to at least 2.4C of heating, a disastrous level.

Some countries have tried to argue that revising NDCs next year was contrary to the Paris agreement, which requires such revisions only every five years. However, the three architects of the Paris agreement – Laurent Fabius, the French foreign minister who presided over the talks; Laurence Tubiana, his chief diplomat; and Christiana Figueres, the UN climate chief at the time – told the Guardian the treaty allowed for a faster return and called on countries to come back to the negotiating table next year with revisions in line with 1.5C.

This provision for an amendment next year, currently paragraph 29 of the second draft outcome text, is likely to be one of the clauses most strenuously fought over in the closing stages. However, there are other outstanding problems, still the subject of frantic shuttle diplomacy by the UK’s Cop president, cabinet minister Alok Sharma.

These sticking points include:

• Developing country concerns that their needs for finance to adapt to the impacts of the climate crisis are being overlooked. They want at least a doubling of the finance available for adaptation, and want to open up discussions on how to vastly increase the $100bn a year in climate finance, from public and private sources, that was promised them in 2009 for delivery from 2020, but which on current estimates will not be fulfilled until 2023.

• Loss and damage, the term for the impacts of the climate crisis too severe for countries to prepare for or adapt to them. The G77 + China bloc of developing nations – which represents 85% of humanity – are very unhappy about current plans for this subject, which they see as the compensation for climate disasters that rich nations have a moral duty to pay. The Guinea delegate, speaking for the bloc, wants the establishment of a “loss and damage facility”, likely to mean an actual fund rather than a measure to work towards one.

• Article 6 of the Paris agreement, which deals with carbon trading. Some countries want to use carbon offsetting to make up some of their commitments to reduce emissions, but others fear that the proposed rules would lead to a flood of cheap carbon credits that do not represent genuine emissions reductions.

• Disagreements over how countries should measure and report their greenhouse gas emissions. Known as the transparency and accountability provisions, these are also regarded as crucial because some countries are suspected of under-reporting their emissions.

Jennifer Morgan, executive director of Greenpeace International, said the commitments on fossil fuels in the current text were too weak and should be strengthened. But she added: “There’s wording in here worth holding on to and the UK presidency needs to fight tooth and nail to keep the most ambitious elements in the deal. We’ve moved from richer nations largely ignoring the pleas of developing countries for promised finance to tackle climate change, to the beginnings of a recognition that their calls should be met. Now we need developed countries to scale up their offer of support and finance.”

She added: “Negotiators in Glasgow simply have to seize the moment and agree something historic, but they need to isolate the governments who’ve come here to wreck progress and instead listen to the calls of youth and vulnerable nations.”

Tracy Carty, head of Oxfam’s Cop26 delegation, said: “Emission reduction targets over the next decade have us careering towards climate catastrophe. We need an unambiguous deal in Glasgow that commits governments to coming back next year, and every year after that, with improved targets that will keep the goal of 1.5 degrees alive. This is the final countdown. Negotiators should come back to the table armed with commitments that are equal to the challenge that millions of people around the world are facing every day.”

Tasneem Essop, executive director of the Climate Action Network, said it was essential that Cop produced concrete decisions to alleviate the suffering of millions of people worldwide coping with the double impacts of Covid and climate breakdown.

“We will continue fighting for this because this is the litmus test for the success of Cop26,” she said.