2016's heating was further boosted by El Nino, during which global sea-level rose strongly.
Extreme weather and climate conditions, including Arctic "heatwaves", have continued into 2017, after global temperatures set record last year and the world witnessed exceptionally low sea ice and unabated ocean heat, the UN weather agency said.
While global temperatures hit a remarkable 1.1 degree-Celsius above the pre-industrial period, global sea-level touch record highs and the planet's sea-ice coverage dropped more than four million square kilometres below average in November - an unprecedented anomaly for that month, according to the World Meteorological Organisation's (WMO) statement on the state of the Global Climate in 2016.
"This increase in global temperature is consistent with other changes occurring in the climate system," WMO Secretary-General Petteri Taalas said.
"With levels of carbon dioxide in the atmosphere consistently breaking new records, the influence of human activities on the climate system has become more and more evident," Mr Taalas said.
Each of the year since 2001 has seen at least 0.4 degree-Celsius above the long-term average for the 1961-1990 base period, used by the UN agency as a reference for climate change monitoring.
The 2016 heating was further boosted by the powerful El Nino weather system, during which global sea-level also rose very strongly.
Similarly, carbon dioxide levels in the atmosphere reached the symbolic benchmark of 400 parts per millions in 2015 - the latest year for which WMO global figures are available - and will not fall below that level for many generations to come because of the long-lasting nature of carbon dioxide.
"The extreme weather patterns are continuing in 2017 adding that at least three times so far this winter, the Arctic saw what can be called the Polar equivalent of a heatwave, with powerful Atlantic storms driving an influx of warm, moist air," WMO said.
"This meant that at the height of the Arctic winter and the sea ice refreezing period, there were days which were actually close to melting point," it said.
In the US alone, 11,743 warm temperature records were broken or tied in February, according to the US National Oceanic and Atmospheric Administration, said the UN agency.
"Even without a strong El Nino in 2017, we are seeing other remarkable changes across the planet that are challenging the limits of our understanding of the climate system," said World Climate Research Programme Director David Carlson.
"We are now in truly uncharted territory," Mr Carlson added.