The World Meteorological Organisation (WMO) says the world is getting hotter and humans are to blame.
A report by the United Nations organisation ahead of the UN climate talks in South Africa says 2011 was the tenth warmest year on record.
The WMO warns increasing global average temperatures are expected to amplify floods, droughts and other extreme weather patterns.
Its deputy secretary-general Jerry Lengoasa says the science is solid and proves unequivocally that the world is warming, and that this warming is due to human activities.
He was speaking to reporters in Durban, where representatives of almost 200 nations are gathered for the talks.
The WMO says the warmest 13 years of average global temperatures have all occurred in the 15 years since 1997.