The deep, freezing winter continues in Sweden - with extremely cold temperatures breaking records. Meanwhile, global warming is reaching record highs. How does this all add up?
For the seventh month in a row, December set a global temperature record. The average temperature was 1.78 degrees above pre-industrial levels, according to the EU's climate service, Copernicus. 2023 was also the warmest year on record worldwide.
But in Sweden, December was colder than normal for the third year in a row, according to preliminary data from SMHI. The cold winter continued into the new year, with extremely cold temperatures breaking records and causing traffic chaos.
How does all this supposedly contradictory weather fit together?
– It's all about the difference between climate and weather, says Michael Tjernström, professor emeritus of boundary layer meteorology at Stockholm University.
– The Earth's average temperature is still rising. In a few places there is winter chaos, while everywhere else is much warmer than usual. So if you look at the Earth as a whole, it is still warmer than it used to be.
Climate is an average of weather over a long period - usually statistics are collected in a data series covering at least 30 years. Weather, on the other hand, is what you see outside your window right now. It varies greatly from place to place, day to day, and year to year.
– We don't have to go very far back in time to remember when we had quite a few consecutive snow-free winters in southern Sweden. And it's not so long ago that the temperature on Christmas Eve was higher than on Midsummer's Eve, says Tjernström.
– Many of the cold records broken in Norrland during the recent cold snaps were not very old. Statistics show that such cold weather is rarer today than it was 50 years ago. We have short memories and forget how it used to be.
Without global warming, would this winter have been even colder?
– Without global warming, it would have been different, says Tjernström.
– The weather is essentially random, or stochastic, meaning that except for seasonal variations, it is determined by chance. But if we had the same without global warming, it would have been even colder this winter.