- The announcement comes several hours after the scheduled Friday evening deadline.
- Delegates had struggled to resolve major sticking points, such as phasing out coal, fossil fuel subsidies and financial support to low-income countries.
- The U.N. meeting in Glasgow, Scotland, was billed as humanity's last and best chance to keep the all-important goal of 1.5 degrees Celsius alive.
Negotiators from nearly 200 countries at the COP26 summit on Saturday reached an agreement to try to prevent progressively worse and potentially irreversible climate impacts.
The announcement comes several hours after the scheduled Friday evening deadline.
Delegates had struggled to resolve major sticking points, such as phasing out coal, fossil fuel subsidies and financial support to low-income countries.
India, among the world's biggest burners of coal, raised a last-minute change of fossil fuel language in the pact, going from a "phase out" of coal to a "phase down." After initial objections, opposing countries ultimately conceded.
In an emotional address to assembled delegates, the U.K.'s COP26 President Alok Sharma said he was "deeply sorry" for the way the process had unfolded. "I understand the deep disappointment. It's also vital we protect this package," Sharma said.
The U.N. meeting in Glasgow, Scotland, was billed as humanity's last and best chance to keep the all-important goal of 1.5 degrees Celsius alive. This temperature threshold refers to the aspirational target inscribed in the landmark 2015 Paris Agreement.
Keeping average temperatures from surpassing this level requires the world to almost halve greenhouse gas emissions in the next 8 years and reach net-zero emissions by 2050. It is critically important to prevent the worst of what the climate crisis has in store.
The world's leading scientists have warned the world has already warmed roughly 1.1 degrees Celsius above pre-industrial levels and the latest projections, despite numerous pledges at the Glasgow summit, show the world is on track for a rise of 2.4 degrees Celsius by the end of the century.
U.N. Secretary General António Guterres had bluntly warned the carbon-cutting pledges on the table during the final throes of the marathon talks were "very probably" not enough to avert a climate catastrophe. He told the Associated Press news agency that the goal of keeping 1.5 degrees Celsius alive was on "life support."
"The road to 1.5 just got harder when these talks should have cleared the way to making it a whole lot easier," Rachel Kennerley, climate campaigner of environmental group Friends of the Earth, said in a statement Saturday.
The Glasgow Climate Pact is the first time the outcome of an international climate summit has explicitly mentioned fossil fuels. However, an earlier commitment to phase out coal and fossil fuel subsidies was subsequently watered down to refer only to "unabated" coal and "inefficient" fossil fuel subsidies. India then raised a last-minute intervention to amend the wording to replace it with "phase down."
Several countries expressed their grievances to this change and environmental experts are deeply concerned the updated terminology creates a loophole to delay urgently needed climate action.
An analysis published by Global Witness on Monday found there were more delegates associated with the fossil fuel industry at COP26 than from any single country. It raised serious questions about the credibility of the talks, particularly because it is the burning of fossil fuels that is the chief driver of the climate crisis.
Researchers have repeatedly stressed that the best weapon to tackle rising global temperatures is to cut greenhouse gas emissions as quickly as possible.
The two-week summit saw a blizzard of climate pledges designed to meet the moment, with countries promising to end and reverse deforestation, move away from coal and reduce methane emissions by 30% by 2030.
The U.S. and China, the world's two largest emitters, surprised many by agreeing to work together this decade to prevent global heating from surpassing 1.5 degrees Celsius. And a new first-of-its-kind alliance was also launched with countries and subnational groups committing to setting an end date to oil and gas use and halting granting new licenses for exploration.
Business leaders and financial institutions, meanwhile, pledged to invest more in "net zero-aligned projects." This has since been criticized, however, for missing the point on fossil fuels.
Low-income countries arrived in Glasgow determined to secure compensation for climate-linked "loss and damage," a term used by the U.N. to refer to the destruction already being inflicted on lives, livelihoods and infrastructure.
Those on the frontlines of the climate crisis, which are the least responsible for climate change, have long sought financial support from high-income countries to compensate them for this damage. Rich nations, such as the U.S., U.K. and European Union, have been reluctant to accept liability.
The agreement, which is not legally binding, falls short of setting up a fund to compensate countries for climate-linked loss and damage. The G-77 group of developing countries expressed "extreme disappointment" at this omission.
Shauna Aminath, minister of environment for the Maldives, said on Saturday: "For some, loss and damage may be the beginning of conversation and dialogue, but for us, this is a matter of survival."
"This does not bring hope to our hearts, but serves as yet another conversation where we put our homes on the line while those who have other options decide how quickly they want to act to save those who don't," Aminath said.
—CNBC's Jessica Bursztynsky contributed to this report.