The United Nations' weather and climate agency, the World Meteorological Organization (WMO), said 2017 is set to become one of the hottest years on record, after 2015 and 2016, mainly because of the El Nino phenomenon.
Last year set a record for Earth's average global temperature.
The WMO announcement was made on Monday, during the opening of the latest United Nations (UN) climate change conference, held in the German city of Bonn this year.
Some 25,000 scientists, envoys, lobbyists and environmental activists have descended on the city to talk about realising the goals of the 2015 Paris climate change accord.
The WMO said key indicators of climate change -- such as rising carbon-dioxide concentrations in the atmosphere, rising sea levels and the acidification of oceans -- "continue unabated" this year.
It said the global mean temperature from January to September this year was about half a degree warmer than the average for the period between 1981 and 2010, which was estimated to be 14.31 degrees Celsius.
This year has been marked by higher-than-average rainfall in places including western China, southern South America and the contiguous United States, the organization said. It has also been marked by lower-than-average coverage areas for Arctic sea ice.