Weather and climate extremes have continued into 2017 after last year saw record breaking temperatures, the World Meteorological Organisation (WMO) said.
Global average temperatures were 1.1C above pre-industrial levels in 2016, slightly above the previous record set in 2015, an annual statement on the state of the global climate said.
Oceans were unusually warm, global sea levels rose sharply, Arctic sea ice was well below average for most of the year and severe droughts hit southern and eastern Africa and Central America.
Extreme conditions have continued into 2017, with the Arctic experiencing the "Polar equivalent of a heatwave" at least three times this winter, while Antarctic sea ice has been at a record low, the WMO said.
Changes in the Arctic have influenced weather in other parts of the world, with balmy weather in Canada and the US and unusually cold conditions in parts of the Arabian peninsula and North Africa.
Prolonged and extreme heat has hit parts of Australia in January and February.
The continuing extremes this year come despite the fading of 2016's strong El Nino conditions, a phenomenon in the Pacific which pushes up global temperatures and affects weather patterns.
We are seeing other remarkable changes across the planet that are challenging the limits of our understanding of the climate system
World Climate Research Programme director David Carlson said: "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."
"We are now in truly uncharted territory."
In 2016, El Nino created around 0.1C to 0.2C warming on top of long-term temperature rises caused by human activity.
WMO secretary-general Petteri Taalas said: "This report confirms that the year 2016 was the warmest on record - a remarkable 1.1C above the pre-industrial period, which is 0.06C above the previous record set in 2015."
"This increase in global temperature is consistent with other changes occurring in the climate system."
He added: "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."
Global sea ice dropped more than four million square kilometres below average in November.
Arctic sea ice saw its lowest maximum cover at the end of winter in records dating back to 1979.
Sea levels rose 15mm from November 2014 to a new record high in February 2016, much higher than the recent trend of 3-3.5mm a year.
Seas were very warm, contributing to significant coral bleaching and death.
Southern Africa begin 2016 in severe drought, while 2016 was the driest on record over the Amazon Basin and there was drought in north east Brazil.
The Yangtze basin in China experienced its most significant flood season since 1999 and it was the wettest year on record across the country, while Hurricane Matthew caused widespread suffering in Haiti and significant economic losses in the US.
There were heatwaves in southern Africa and parts of Asia and record temperatures in parts of the Middle East.