And it said the extreme weather and climatic conditions are continuing this year.
Using data from around the world, the WMO confirmed 2016 as the warmest ever.
It also saw the warmest ever global sea surface temperatures, while sea levels continued to rise and global sea ice levels in November fell to a record low.
At the same time coral reefs suffered “significant” bleaching and mortality due to the warming of the seas.
The annual report was released in the face of the Trump administration undermining the Paris climate agreement, taking an axe to US climate change programmes, and Budget Director Mick Mulvaney describing the schemes as a “waste of your money”.
But Professor Sir Robert Watson, of the Tyndall Centre for Climate Change Research, University of East Anglia, said:
“The Trump Administration and senior Republicans in Congress continue to bury their heads in the sand and state that climate change is a hoax and does not need to be addressed. We are now living in an evidence-free world, where facts are irrelevant.
How much more evidence does the world need
“Our children and grandchildren will look back on the climate deniers and ask how they could have sacrificed the planet for the sake of cheap fossil fuel energy when the cost of inaction exceeds the cost of a transition to a low-carbon economy.
“How much more evidence does the world need to recognise the dangers confronting our society?
The WMO said levels of the greenhouse gas carbon dioxide – raised by the burning of fossil fuels since the Industrial Revolution – hit a record 400 parts per million in 2015, the most recent year for which figures are available.
They combined with a powerful El Niño – a periodic warming of the east-central Pacific Ocean – to force up temperatures.
The Arctic has this winter seen at least three heatwaves, with temperatures close to the melting point for sea ice.
Antarctic sea ice has also been at a record low.
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.
“Globally averaged sea surface temperatures were also the warmest on record, global sea levels continued to rise, and Arctic sea-ice extent was well below average for most of the year.
“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.”
Mr Taalas said the WMO can now “demonstrate clearly the existence of links between man-made climate change and many cases of high impact extreme events in particular heatwaves”.
And it said each of the 16 years since 2001 has been at least 0.4C above the long-term average for the 1961-1990 base period.
And the dramatic changes are continuing into the current year, according to the WMO. which said ocean heat content may have increased even more than previously reported.
World Climate Research Programme Director David Carlson said: “Even without a strong El Niño 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.”