2024/01/06-08 Scandinavian Cold Spell
Scandinavian cold spell mostly weakened by human-driven climate change
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.
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.
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.
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.
-Gabriele Messori, Uppsala University, Sweden📨email@example.com 🗣️Italian, English, French, Swedish
Additional Information : Complete Output of the Analysis
NB1: The following output is specifically intended for researchers and contain details that are fully understandable only by reading the methodology described in Faranda, D., Bourdin, S., Ginesta, M., Krouma, M., Noyelle, R., Pons, F., Yiou, P., and Messori, G.: A climate-change attribution retrospective of some impactful weather extremes of 2021, Weather Clim. Dynam., 3, 1311–1340, https://doi.org/10.5194/wcd-3-1311-2022, 2022.
NB2: Colorscales may vary from the ClimaMeter figure presented above.
The figure shows the average of surface pressure anomaly (msl) (a), average 2-meter temperatures anomalies (t2m) (e), cumulated total precipitation (tp) (i), and average wind-speed (wspd) in the period of the event. Average of the surface pressure analogs found in the counterfactual [1979-2000] (b) and factual periods [2001-2022] (c), along with corresponding 2-meter temperatures (f, g), cumulated precipitation (j, k), and wind speed (n, o). Changes between present and past analogues are presented for surface pressure ∆slp (d), 2 meter temperatures ∆t2m (h), total precipitation ∆tp (i), and windspeed ∆wspd (p): color-filled areas indicate significant anomalies with respect to the bootstrap procedure. Violin plots for past (blue) and present (orange) periods for Quality Q analogs (q), Predictability Index D (r), Persistence Index Θ (s), and distribution of analogs in each month (t). Violin plots for past (blue) and present (orange) periods for ENSO (u), AMO (v) and PDO (w). Number of the Analogues occurring in each subperiod (blue) and linear trend (black). Values for the peak day of the extreme event are marked by a blue dot. Horizontal bars in panels (q,r,s,u,v,w) correspond to the mean (black) and median (red) of the distributions.