GENEVA, Switzerland– Global heat records were "smashed" last year, the UN confirmed Tuesday, with 2023 rounding out the hottest decade on record, as heatwaves stalked oceans and glaciers suffered record ice loss.

The United Nations' World Meteorological Organization issued its annual State of the Climate report, confirming preliminary data indicating that 2023 was by far the hottest year ever recorded.

And it came at the end of "the warmest 10-year period on record", the WMO report said.

UN chief Antonio Guterres said the report showed "a planet on the brink".

"Earth's issuing a distress call," he said, pointing out that "fossil fuel pollution is sending climate chaos off the charts", and warning that "changes are speeding up".

The WMO said the average near-surface temperature was 1.45 degrees Celsius above pre-industrial levels last year -- dangerously close to the critical 1.5-degree threshold that countries agreed to avoid passing in the 2015 Paris climate accords.

"Never have we been so close... to the 1.5C lower limit of the Paris Agreement," WMO chief Andrea Celeste Saulo warned in a statement.

- 'Red alert' -

The report, she said, should be seen as a "red alert to the world".

Going through the data, the organisation found that "records were once again broken, and in some cases smashed", warning that the numbers "gave ominous new significance to the phrase 'off the charts'."

Saulo stressed that climate change was about much more than temperatures.

"What we witnessed in 2023, especially with the unprecedented ocean warmth, glacier retreat and Antarctic sea ice loss, is cause for particular concern."

One especially worrying finding was that marine heatwaves gripped nearly a third of the global ocean on an average day last year.

And by the end of 2023, more than 90 percent of the ocean had experienced heatwave conditions at some point during the year, the WMO said.

More frequent and intense marine heatwaves will have "profound negative repercussions for marine ecosystems and coral reefs", it warned.

At the same time, it warned that key glaciers worldwide suffered the largest loss of ice ever since records began in 1950, "driven by extreme melt in both western North America and Europe".

In Switzerland, where the WMO is headquartered, Alpine glaciers had for instance lost 10 percent of their remaining volume in the past two years alone, it said.

The Antarctic sea ice extent was also "by far the lowest on record", WMO said.

- Rising sea levels -

In fact, it pointed out, its maximum extent at the end of the southern winter was around one million square kilometres below the previous record year -- equivalent to the size of France and Germany combined.

The continued ocean warming combined with the rapidly melting glaciers and ice sheets also drove the sea level last year to its highest point since satellite records began in 1993, WMO said.

The agency stressed that the global mean sea level rise over the past decade (2014-2023) was more than double the rate in the first decade of satellite records.

It highlighted that the dramatic climate shifts are taking a heavy toll on people worldwide, fuelling extreme weather events, flooding and drought, which trigger displacement and drive up biodiversity loss and food insecurity.

"The climate crisis is THE defining challenge that humanity faces and is closely intertwined with the inequality crisis," Saulo said.

- 'Glimmer of hope' -

The number of people who are considered acutely food insecure around the world has more than doubled, from 149 million people prior to the Covid-19 pandemic to 333 million at the end of 2023, WMO pointed out.

The UN's weather and climate agency did however highlight one "glimmer of hope": surging renewable energy generation.

Last year, renewable energy generation capacity -- mainly from solar, wind and hydropower -- increased by nearly 50 percent from 2022, it said.

Guterres also emphasised that there was an upside to the findings.

The world, he insisted, still has a chance to keep the planet's long-term temperature rise below the 1.5C threshold and "avoid the worst of climate chaos".

"We know how to do it."