This year has been one of the hottest since records began, as the world comes to the end of a decade of “exceptional” heat.
Global temperatures have been 1.1C above pre-industrial levels, data from January to October shows.
This puts the year on course to be the second or third warmest in records dating to the 19th century.
The past decade and five years have also been the hottest, the World Meteorological Organisation said.
WMO secretary-general Petteri Taalas added: “If we don’t take urgent action, we are heading for an increase of more than 3C by the end of the century with ever more harmful impacts on human well-being.
“On a day-to-day basis, the impacts of climate change play out through extreme and abnormal weather ."
United Nations body the WMO warns sea levels are rising ever faster, ice is melting and “once in a century” heatwaves and floods are becoming more regular occurrences.
Millions were forced from their homes due to extreme events such as cyclones and hurricanes.
The past year has featured two major heatwaves in Europe, with a temperature record of 38.7C set in the UK.
The report is released as countries meet in Madrid for UN climate talks.
Prof Tim Osborn, from UAE, said: “The five warmest years for average global surface temperature since records began in 1850 have all occurred in the last five years; by contrast the five coldest years all occurred before 1912.
“This is climate change and not a coincidence.”
