Every major global climate record was broken last year and 2024 could be worse, the World Meteorological Organization (WMO) said on Tuesday, with its chief voicing particular concern about ocean heat and shrinking sea ice.

The UN weather agency said in its annual State of the Global Climate report that average temperatures hit the highest level in 174 years of record-keeping by a clear margin, reaching 1.45 degrees Celsius above pre-industrial levels.

Ocean temperatures also reached the warmest in 65 years of data with over 90 percent of the seas having experienced heatwave conditions during the year, the WMO said, harming food systems.

WMO Secretary-General Celeste Saulo, who took over the job in January, said she was sounding the “red alert” about the state of the climate.”

She told reporters in Geneva that ocean heat was particularly concerning because it was "almost irreversible," possibly taking millennia to reverse.

Climate change, driven by the burning of fossil fuels, coupled with the emergence of the natural El Nino climate pattern, pushed the world into record territory in 2023.

WMO's head of climate monitoring, Omar Baddour, said there was a "high probability" that 2024 would set new heat records, saying that the year after an El Nino was typically warmer still.

Tuesday's report showed a big plunge in Antarctic sea ice, with the peak level measured at 1 million km2 below the previous record - an area roughly equivalent to the size of Egypt. 

That trend, combined with ocean warming which causes water to expand, has contributed to a more than doubling of the rate of sea-level rise over the past decade compared with the 1993-2002 period, it said.

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Ocean heat was concentrated in the North Atlantic with temperatures an average 3 degrees Celsius above average in late 2023, the report said. Warmer ocean temperatures affect delicate marine ecosystems and many fish species have fled north from this area seeking cooler temperatures.

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(Production: Cecile Mantovani)