The annual Emissions Gap report, which assesses countries' promises to tackle climate change compared with what is needed, finds the world faces between 2.5C and 2.9C of warming above preindustrial levels if governments do not boost climate action.
At 3C of warming, scientists predict the world could pass several catastrophic points of no return, from the runaway melting of ice sheets to the Amazon rainforest drying out.
World leaders will soon meet in Dubai for the annual U.N. climate summit COP28 with the aim of keeping the Paris Agreement warming target of 1.5C alive.
But the new U.N. report does little to inspire hope that this goal remains in reach, finding that planet-warming greenhouse gas emissions must fall by 42% by 2030 to hold warming at 1.5C (2.7F).