The unusually warm conditions in Europe that marked the festive season broke records in several countries on the continent, on New Year's Eve and New Year's Day, the UN weather agency said.

The UN World Meteorological Organization (WMO) linked the record-breaking heat  to widely accepted peer-reviewed scientific data from the UN Intergovernmental Panel on Climate Change (IPCC) indicating that the frequency of cold spells and frost days "will decrease."

"Strong declines in glaciers, permafrost, snow cover extent, and snow seasonal duration at high latitudes or altitudes are observed and will continue in a warming world," the IPCC said.

According to the UN agency, New Year temperatures soared above 20 degrees Celsius in many European countries, even in central Europe.

National and many local temperature records for December and January were also broken in several countries, from southern Spain to eastern and northern parts of Europe, the WMO said.

At Spain's Bilbao airport, a reading of 25.1 degrees Celsius on January 1 smashed the previous all-time record established 12 months earlier, by 0.7 degrees Celsius.

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And in the eastern French city of Besançon, which is usually chilly at this time of year, temperatures hit a new all-time high of 18.6 degrees Celsius on New Year's Day, 1.8 degrees Celsius above the previous record, dating back to January 1918.

In the German city of Dresden, the 1961 New Year's Eve record of 17.7 degrees Celsius was left trailing by the 19.4 degrees Celsius reading taken on December 31, 2022, just as Poland's Warsaw residents saw in the new year with temperatures peaking at 18.9 degrees Celsius, a staggering 5.1 degrees Celsius higher than the previous all-time record for January, from 1993.

Further north, on Denmark's Lolland island, 2023 started with a new high of 12.6 degrees Celsius, overtaking the 12.4 degrees Celsius record set in 2005.

The WMO attributed the warm spell in Europe to a high-pressure zone over the Mediterranean region which encountered an Atlantic low-pressure system.

Their interaction induced a strong south-west flux that brought warm air from north-western Africa to middle latitudes, the UN agency said, adding that this hotter-than-normal air was further warmed when passing the North Atlantic, due to a higher-than-normal sea surface temperature.

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Highlighting the influence of warmer sea waters on weather patterns, the WMO noted that in the eastern North Atlantic, sea surface temperature was 1 to 2 degrees Celsius higher than normal, and near the coasts of Iberia, even more.

All this caused record-breaking heat in several European countries on New Year's Eve and New Year's Day, the WMO said.

The weather extremes experienced in Europe are projected to carry on increasing, the WMO said, as it referenced a recent analysis published with "high confidence" by the IPCC.

"Regardless of future levels of global warming, temperatures will rise in all European areas at a rate exceeding global mean temperature changes, similar to past observations," the IPCC said.