According to the World Meteorological Organisation (WMO) the average global temperatures for 2015 are running “well above” any previous 12 month period.
The researchers say the five year period from 2011 to 2015 was also the warmest on record.
The rise, they say, is because of a combination of a strong El Nino weather pattern and human-induced global warming.
The organisation says the global average surface temperature for 2015 was 0.73 degrees C above the 1961-1990 average.
“This is all bad news for the planet,” the WMO secretary-general Michel Jarraud says.
“2015 is likely to be the hottest year on record, with ocean surface temperatures at the highest level since measurements began. It is probable that the 1C threshold will be crossed.”
Researchers have agreed the latest data from the WMO reinforces the view human emissions of carbon dioxide, from burning fossil fuels, are continuing to heat the Earth beyond natural variability.