The WMO's provisional State of the Global Climate report confirms that 2023 will be the warmest year on record by a large margin, replacing the previous record-holder 2016, when the world was about 1.2C warmer than the pre-industrial average.
It adds to the urgency world leaders face as they wrestle with phasing out fossil fuels at the United Nations annual climate summit COP28, which begins on Thursday in Dubai.
"Greenhouse gas levels are record high. Global temperatures are record high. Sea level rise is record high. Antarctic sea ice record low," WMO secretary-general Peterri Taalas said.
The report's finding, however, does not mean the world is about to cross the long-term warming threshold of 1.5C that scientists say is the ceiling for avoiding catastrophic climate change under the 2015 Paris Agreement.
For that, the level of warming would need to be sustained for longer.
Already, a year of 1.4C has provided a frightening preview of what permanently crossing 1.5C might mean.
This year, Antarctic sea ice reached its lowest winter maximum extent on record, some 1 million square kilometres less than the previous record.
Swiss glaciers lost about 10 per cent of their remaining volume during the past two years, the report said.
And wildfires burned a record area in Canada, amounting to about five per cent of the country's woodlands.
Climate change, driven by the burning of fossil fuels, combined with the emergence of the natural El Nino climate pattern in the Eastern Pacific pushed the world into record territory this year.
Next year could be worse, the scientists said, as El Nino's impacts are likely to peak this winter and drive higher temperatures in 2024.
