In another sign of climate change driven by human activity, the mercury hit 4 degrees Celsius in Longyearbyen, the main town of the Svalbard archipelago in the Arctic, on December 22 -- warmer than both Seville and Ankara, which recorded temperatures of three and one Celsius respectively on that day.

"It's actually a record-setting year," said Hans Olav Hygen, a climatologist at the Norwegian Meteorological Institute.

"Many places in Norway had a record hot summer with a strong heatwave in July," he told AFP.

"This, of course, affects the full report, and we also saw before Christmas the fairly warm late autumn (and) start of the winter."

Norway's national temperatures were 1.5C higher than usual last year compared to the average during the period 1991-2020, and 2.8C above the average during the pre-industrial era (1871-1900), according to the institute.

"We expect the temperatures that we saw this year (2025) to become more frequent in the future," Amalie Skalevag, another researcher at the institute, said in a statement.

A large part of northern Europe experienced an unusual heatwave in July, to the point where emergency services in southeastern Finland were strained and Finnish municipalities turned their ice rinks into cool refuges for the public.

Last month, large parts of Norway celebrated Christmas without snow, including the capital Oslo in the south and Trondheim further north, where residents told AFP the temperature soared to an unusually mild 6C for the holiday.

Across the North Sea, Britain also recorded its hottest year in 2025, according to its Met Office.