The climate pact, sealed after intense last-minute wrangling at the UK-hosted UN conference, recognised the need for cuts in carbon emissions but put off the pledges needed to achieve them until next year.
The deal did however make enough progress to allow summit president Alok Sharma to say that it kept alive the hope of limiting global warming to 1.5C.
But in a dramatic last-minute intervention, India and China significantly watered down commitments on fossil fuels, securing the change of a single word to ensure the pact calls for coal power generation to be “phased down” rather than “phased out”.
In a rare show of emotion, Mr Sharma struggled to hold back tears as he acknowledged the furious reaction of Europe and low-lying island states, saying he was “deeply sorry” for the revision, but insisted: “It is vital we protect the package.”
Earlier, he had urged bickering delegates not to unravel the “fine and fragile green thread” of the compromises secured at Glasgow “imperfect though they may be”.
Vulnerable poorer countries were bitterly disappointed that a proposed funding facility to pay for loss and damage from extreme weather events like hurricanes and floods was kicked into the long grass with the promise of a “dialogue” with rich-world donors.
The Maldives warned that any outcome from Glasgow will come “too late” to save the Indian Ocean island state from the threat of rising sea waters.
“What is balanced and pragmatic to other parties will not help the Maldives adapt in time,” said climate change minister Shauna Aminath. “For us, this is a matter of survival … The difference between 1.5 and 2 degrees is a death sentence for us.”
UN secretary general Antonio Guterres said the “compromise” deal had failed to achieve the goals of ending fossil fuel subsidies, phasing out coal, putting a price on carbon, building the resilience of vulnerable communities and making good on a 12-year-old promise for $100bn a year of rich-world support for developing countries.
“Our fragile planet is hanging by a thread,” said Mr Guterres. “We are still knocking on the door of climate catastrophe. It is time to go into emergency mode or our chance of reaching net zero will itself be zero.”
The former Irish president, and member of The Elders group of international statespeople, Mary Robinson also criticised the outcome of the summit, calling it a “historically shameful dereliction of duty” on the part of leaders who were not “on panic mode”.
Thrashed out in an all-night negotiating session after the summit missed its Friday deadline for a decision, the final agreement reaffirmed the goal set in the 2015 Paris accord of keeping temperature rises “well below” 2C above pre-industrial levels and pursuing efforts to limit them to 1.5C – which scientists believe will stave off the most catastrophic consequences of global warming.
But the respected Carbon Tracker website said commitments made so far would still see warming of 2.4C, while according to UN estimates greenhouse gas emissions are set to rise 16 per cent by 2030, rather than fall by the 45 per cent demanded in the new agreement.
In perhaps the most significant advance made at Glasgow, a “ratchet” mechanism designed to force continual escalation of climate action was accelerated, requiring states to come forward with enhanced emission reduction plans by the time of the Cop27 summit in Egypt at the end of 2022.
The move to annual reporting, from the five-yearly cycle agreed in Paris, was opposed by China and India, but was seen by environmentalists as a key measure in speeding up action in what was described as “this crucial decade”.
Declaring the completion of the agreement with a bang of the gavel on Saturday evening, Mr Sharma said that “history has been made here in Glasgow”.
Boris Johnson also said he hoped it would mark “the beginning of the end for climate change”.
“There is still a huge amount more to do in the coming years,” said the prime minister. “But today’s agreement is a big step forward and, critically, we have the first-ever international agreement to phase down coal and a roadmap to limit global warming to 1.5C.”
But Labour leader Sir Keir Starmer branded the two-week summit a “missed opportunity”, saying that Mr Johnson himself bore much of the responsibility for its limited achievements.
“The prime minister has hindered not helped,” said Sir Keir. “Boris Johnson never treated this summit with the seriousness it deserved, nor built the trust so critical to its success.”
And Oxfam executive director Gabriela Bucher said: “Clearly some world leaders think they aren’t living on the same planet as the rest of us. It seems no amount of fires, rising sea levels or droughts will bring them to their senses to stop increasing emissions at the expense of humanity.”
Greenpeace International executive director Jennifer Morgan said the “meek and weak” deal left the 1.5C goal “only just alive”.
“While the deal recognises the need for deep emissions cuts this decade, those commitments have been punted to next year,” said Ms Morgan. “Young people who’ve come of age in the climate crisis won’t tolerate many more outcomes like this. Why should they when they’re fighting for their futures?”
She dismissed the eleventh-hour ambush by India and China as less significant than the fact that fossil fuels were included for the first time in a UN climate decision.
“They changed a word but they can’t change the signal coming out of this Cop, that the era of coal is ending,” she said.
While Cop’s outcome does not achieve the global aspiration of limiting warming to 1.5C, it keeps the prospect within reach, with a series of processes to close emissions gaps and loopholes in the years leading up to 2030.
Seve Paeniu, the climate minister of the Pacific island state of Tuvalu, said the summit had delivered “a strong message of hope, a strong message of promise, a strong message of ambition”.
Holding up a photograph of his three grandchildren, Mr Paeniu said: “I will be able to tell them that Glasgow has made a promise to save their future. That will be the best ever Christmas gift I will present to them .”
US climate envoy John Kerry was involved in intense discussions with Chinese and Indian delegates on the floor of the conference hall as they forced the last-minute climbdown on coal.
Accepting the necessity of compromise, he told delegates: “We all know the adage of negotiations: you can’t let the perfect be the enemy of the good.
“And this is good. It is a powerful statement.”
Sepi Golzari-Munro, the acting director of the Energy and Climate Intelligence Unit (ECIU), said that, while “not perfect”, the Glasgow pact “delivered more than many expected”.
“The UK presidency used its significant diplomatic skill to reach a conclusion that parties could agree upon and built momentum on tackling climate change that has kept the Paris Agreement goals within reach,” said Ms Golzari-Monro.
But campaign group ActionAid International said the failure to deliver funding to help poor countries recover from warming-linked natural disasters was “an insult to the millions of people whose lives are being torn apart by the climate crisis”.
The director of Global Justice Now, Nick Dearden, said that Mr Johnson’s government had set Cop26 up to fail by making it inaccessible to campaigners from the global south while opening it up to corporate interests.
The result, he said, was a “hollowed-out agreement shows that, for all the lip service they paid, world leaders and big business have not listened”.
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