Scandinavian cold spell mostly weakened by human-driven climate change

Press Summary (First published 2024/01/18)

• Pressure patterns similar to that producing the January 2024 Scandinavian cold spell lead to locally up to 5 °C warmer temperatures in the present than in the past.

• The January 2024 Scandinavian cold spell was a largely unique event.

• Natural climate variability likely played a role in driving the pressure pattern and the associated increase in temperature linked to the January 2024 Scandinavian cold spell, but human-driven climate change may have also contributed. 

Event Description

In early January 2024, Scandinavia experienced unusually low temperatures. The cold spell started in Northern Scandinavia, and then progressed southwards. The dates we chose for this report coincide with the coldest temperatures in central and southern Scandinavia, where the largest population centres are located. Values below -40 °C were recorded for several days in Northern Sweden, with the lowest reading being -43,6 °C in Kvikkjokk-Årrenjarka on the 3rd January. This set a new record for the station, as well as being the coldest temperature recorded in Sweden in the last 25 years. At some locations, the daily average temperature was below -40 °C for three days in a row. The cold air then moved southwards, with several lows below -30 °C in central Sweden on the weekend of the 6th-7th January. Other Nordic countries also faced extremely low temperatures. The cold spell was preceded by or coincided with snowfall in several regions.

The snow and low temperatures led to severe traffic problems, with train circulation in Northern Sweden being suspended for several days, and motorists being stranded on snow-clogged highways overnight in Sweden and Denmark. There were also reports of blackouts and road accidents.

The Surface Pressure Anomalies reveal a weather pattern characterized by high-pressure anomalies over the Norwegian Sea and Scandinavia, with a low pressure to the South. This atmospheric setup led to a significant influx of cold air towards Scandinavia. At many locations, clear skies also led to intense radiative cooling. Temperature Anomalies indicate that most of central-southern Scandinavia and north-eastern Europe experienced strong negative near-surface temperature anomalies, peaking at below -10 °C in our data. Precipitation Data shows precipitation occurring mainly along the northern Norwegian coast and in Central Europe. Relatively windy conditions prevailed in the analysis domain, as shown in Windspeed Data. 

Climate and Data Background for the Analysis

The IPCC AR6 WG1 (IPCC AR6 WGI FR - Page 1839)  report discusses the significant impact of climate change on the frequency and intensity of cold outbreaks in Europe.  According to the IPCC, there is a long-term decreasing frequency of winter cold spells in Europe, and this trend is projected to continue in the future with a high level of confidence. The probability of occurrence of cold spells is expected to decrease and virtually disappear by the end of the century. The frequency of frost days is also very likely to decrease for all scenarios and all time horizons, which will have consequences for agriculture and forests. Additionally, there is a large observed decreasing trend for winter heating energy demand in Europe, which is very likely to continue through the 21st century. The decreases in heating demand are projected to be in the range of 20-30% for Northern Europe, about 20% for central Europe, and 35% for southern Europe by mid-century under the highest greenhouse gases emissions scenarios. Scandinavia fits these trends, and has shown a significant decrease in wintertime cold days in recent decades.

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For the January 2024 Scandinavian cold spell, we have low confidence in the robustness of our approach given the available climate data, as the atmospheric pattern that led to the cold spell is largely unique in the data record.

ClimaMeter Analysis

We analyze here (see Methodology for more details) how events similar to the pressure pattern leading to the January 2024 Scandinavian cold spell have changed in the present (2000–2021) compared to what they would have looked like if they had occurred in the past (1979–2000) in the region [5°E 35°E 45°N 70°N]. The Surface Pressure Changes show that the high-pressure system over the Norwegian Sea and Scandinavia has become more intense by up to 5 hPa, but has also shifted to the West. Temperature Changes show that similar events produce milder conditions (locally exceeding 5 °C)  in the present than in the past over much of Central Europe, Central-Southern Scandinavia and the Baltic Sea. Other regions of Scandinavia show little temperature changes. Examining Precipitation Changes reveals very limited differences. Windspeed Changes are modest, and reflect the shift of the high-pressure system further to the West. We also find no major shift in the seasonal occurrence of Similar Past Events. Considering the affected urban areas of Oslo, Stockholm and Helsinki, our analysis finds that they are (1-5 °C) warmer in the present than in the past during similar events. Oslo also displays a moderate increase in windspeed by 2 km/h. 

Finally, we find that sources of natural climate variability, notably the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation, may have influenced the event. This suggests that the changes we see in the event compared to the past may be due to human-driven climate change, with a contribution from natural variability.

Conclusion

Based on the above, we conclude that pressure patterns similar to that causing the January 2024 Scandinavian cold spell are up to 5 °C warmer in the present than they have been in the past. We interpret the January 2024 Scandinavian cold spell as a largely unique event for which natural climate variability played a role.

Contact Authors

-Gabriele Messori, Uppsala University, Sweden📨gabriele.messori@geo.uu.se  🗣️Italian, English, French, Swedish

-Stavros Dafis, National Observatory of Athens, Greece 📨 sdafis@noa.gr 🗣️ Greek, English, French

-Davide Faranda, IPSL-CNRS, France  📨davide.faranda@lsce.ipsl.fr  🗣️French, Italian, English