After arduous talks in Valencia, Spain, scientists agreed a document they hope will shape debate on the next phase of the fight against climate change.
It declared the fact of global warming "unequivocal", and said it may bring "abrupt and irreversible" impacts.
The text will be officially launched by UN chief Ban Ki-moon on Saturday.
Delegates to the Intergovernmental Panel on Climate Change (IPCC) summarised thousands of pages of scientific analysis, bringing together elements of the three reports already released this year, on the science of climate change, impacts and adaptation, and options for mitigating the problem.
"This is the strongest report yet by the IPCC - but says that there is still time to act," Bill Hare, an Australian climate scientist and one of the authors, told Reuters.