This year has been forecast to be one of the three hottest years on record.
It found the average global temperature from January to September 2017 was round 1.1°C above pre-industrial era.
Its report suggests long term indicators of climate change such as increasing carbon dioxide concentrations, sea level rise and ocean acidification continue unabated.
WMO Secretary-General Petteri Taalas said: “The past three years have all been in the top three years in terms of temperature records. This is part of a long term warming trend.
“We have witnessed extraordinary weather, including temperatures topping 50°C in Asia, record-breaking hurricanes in rapid succession in the Caribbean and Atlantic reaching as far as Ireland, devastating monsoon flooding affecting many millions of people and a relentless drought in East Africa.
“Many of these events – and detailed scientific studies will determine exactly how many – bear the tell-tale sign of climate change caused by increased greenhouse gas concentrations from human activities.”