The Paris climate agreement's goals "are in great peril" and 2024 is on track to break new temperature records, the United Nations warned Monday as COP29 talks opened in Baku.
The period from 2015 to 2024 will also be the warmest decade ever recorded, the UN's World Meteorological Organization (WMO) said in a new report based on six international datasets.
WMO chief Celeste Saulo said she was sounding the "red alert".
"It's another SOS for the planet," she told reporters in Baku.
The warming trend is accelerating the shrinking of glaciers and sea-level rise, and unleashing extreme weather that has wrought havoc on communities and economies around the world.
"The ambitions of the Paris Agreement are in great peril," the WMO climate and weather agency said as global leaders gathered for high-stakes climate talks in Azerbaijan.
Under the Paris agreement, nearly every nation on Earth committed to work to limit warming to "well below" two degrees Celsius above pre-industrial levels, and preferably to below 1.5C.
But the EU climate monitor Copernicus has already said that 2024 will exceed 1.5C.
This does not amount to an immediate breach of the Paris deal, which measures temperatures over decades, but it suggests the world is far off track on its goals.
The WMO, which relies on a broader dataset, also said 2024 would likely breach the 1.5C limit, and break the record set just last year.
"Climate catastrophe is hammering health, widening inequalities, harming sustainable development, and rocking the foundations of peace. The vulnerable are hardest hit," UN chief Antonio Guterres said in a statement.
Analysis by a team of international experts established by the WMO found that long-term global warming was currently likely to be around 1.3C, compared to the 1850-1900 baseline, the agency said.
"We need to act as soon as possible," Saulo said, insisting that the world must "not give up on the 1.5 (ambition)".
Monday's report cautioned that greenhouse gas concentrations in the atmosphere, which lock in future temperature increases even if emissions fall, hit new highs in 2023 and appeared to have climbed further this year.
Ocean heat is also likely to be comparable to the record highs seen last year, it added.
Saulo insisted that "every fraction of a degree of warming matters, and increases climate extremes, impacts and risks.
"Temperatures are only part of the picture. Climate change plays out before our eyes on an almost daily basis in the form of extreme weather," she said.
Saulo pointed to how "this year's record-breaking rainfall and flooding events and terrible loss of life... (had caused) heartbreak to communities on every continent.
"The incredible amount of rain in Spain was a wake-up call about how much more water a warmer atmosphere can hold," she added.
She warned that the string of devastating extreme weather events across the world this year "are unfortunately our new reality".
They are, she said, "a foretaste of our future".
