A pledge to phase out coal gained the support of 23 more countries at the UN climate conference on Thursday, but was shunned by big users of the dirtiest of the fuels that cause global warming.
The Cop26 summit hopes to find ways to keep within reach a target of limiting the global temperature rise to 1.5 degrees Celsius, but the scale of the challenge was underlined by a study showing carbon dioxide emissions have returned to near pre-pandemic levels.
Greenhouse gas emissions from burning coal are the single-biggest contributor to climate change, and weaning the world off coal is considered vital to achieving global climate targets.
The pledge to drop coal did not include Australia, India, the United States and China, which has around half the coal-fired plants operating around the world and plans to build more.
Carbon dioxide emissions fell by 5.4 per cent in 2020 as economies ground to a halt, but the new report by the Global Carbon Project forecast a 4.9 per cent rebound in emissions for this year.
"We were expecting to see some rebound," said the report's lead author Pierre Friedlingstein, a climate modelling researcher at the University of Exeter. "What surprised us was the intensity and rapidity."
It was a stark reminder to leaders in Glasgow of the challenge of preventing more than 1.5C of global warming above pre-industrial levels.
The United Nations says a rise above 1.5C would trigger climate impacts far more catastrophic than the intensifying storms, heatwaves, droughts and floods already being seen.
"I think we can say that the end of coal is in sight," Alok Sharma, British president of the two-week summit, said in detailing the pledge to phase out existing coal-fuelled power plants and to stop building new ones.
The non-binding pledge "has 77 signatories, including 46 countries, such as Poland, Vietnam and Chile, 23 of which are making commitments on ending coal for the first time," he said.
Richer nations agreed to quit coal power by the 2030s and poorer ones by the 2040s. Poland said it was aiming for the 2040s - having previously pledged to stop mining coal in 2049. Indonesia did not agree to the part of the deal on ending finance for new coal plants.
Coal-fired power today produces more than a third of the world's electricity. Many developing countries currently rely on cheap, accessible coal to fuel their economies, just as developed countries did from the Industrial Revolution of the 19th century onwards, despite the costs to the environment and public health.
The International Energy Agency, the world's energy watchdog, said net-zero emissions pledges and promises to cut methane announced at Cop26, if enforced, would enable the world to limit warming to below 2 degrees.
"New @IEA analysis shows that fully achieving all net zero pledges to date & the Global Methane Pledge by those who signed it would limit global warming to 1.8C," IEA chief Fatih Birol wrote on Twitter.
Selwin Hart, special adviser to the UN secretary general on climate action, challenged Mr Birol's assertion.
"Fatih, I heard your numbers. But based on the NDCs that have been submitted, the world is on a 2.7 degree pathway – a catastrophic pathway," Mr Hart said in Glasgow.
"And therefore we are a long way from keeping the 1.5C goal of the Paris Agreement alive. We cannot be complacent. We cannot celebrate before we've done the job," he added.
The UN Environment Programme said poorer countries needed five to 10 times more money to adapt to the consequences of climate change than they are now getting.
Richer countries failed to meet a 2020 deadline for delivering $100 billion a year in "climate finance".
Questions of finance also swirled around the Cop26 coal deal, which some countries said they would not be able to deliver without more financial help.
"We need to have funding to retire coal earlier and to build the new capacity of renewable energy," said Indonesia's finance minister Mulyani Indrawati. The Southeast Asian nation is the world's biggest coal exporter, and relies on the fuel for 65 per cent of its own energy capacity.
It also will be among the first recipients of a multibillion dollar pilot programme to speed a transition to clean energy, along with India, South Africa and the Philippines, the Climate Investment Funds said.
The main aim of Cop26 is to get promises of enough cuts in greenhouse gas emissions to put the world on a clear path towards capping the rise in global temperature - already up 1.1C since pre-industrial times.