The average temperature in 2017 was 1.1 degrees Celsius above pre-industrial levels, “in a clear sign of continuing long-term climate change” caused by greenhouse gases, the UN agency said.
The heat record is held by 2016, at 1.2 degrees above the pre-industrial era, while 2015 and 2017 are tied for second place.
WMO Secretary General, Petteri Taalas, pointed out that 17 of the 18 warmest years on record have occurred in this century.
“The long-term temperature trend is far more important than the ranking of individual years, and that trend is an upward one,” he said.
In the past three years, the arctic region was especially warm, which will have long-lasting effects on sea levels and weather patterns across the globe, according to the Finnish UN chief meteorologist.
Hurricanes caused the costliest damages ever seen in the U.S. in 2017.
In other countries, economic development was slowed or even reversed by cyclones, floods and drought, WMO reported.