40 °C heat extremes are no longer implausible in the Nordic countries

Abstract

The Nordic countries of Norway, Sweden, and Finland have traditionally been characterised by less intense heatwaves than continental Europe. However, during recent events, such as the 2026 heatwave, exceptionally high temperatures have been observed across large parts of Europe, with temperatures of 40 °C reaching further north than previously observed. Such temperatures would pose substantial risks in the Nordics, as people and infrastructure are generally less adapted to extreme heat than in warmer climates. Here, we analyse all available weather forecasts from the European Centre for Medium-Range Weather Forecasts’ seasonal prediction system, corresponding to 7308 years of simulated summers, and show that 40 °C cannot be considered implausible in the Nordic countries. We estimate that the annual probability of reaching 40 °C somewhere in the Nordics is 0.53% in 2025 (95% confidence interval: 0.38–0.70%), which represents a six-fold increase since 1981. Furthermore, the annual probability of exceeding the observed national heat record so far is highest in Norway, being 10.9% already under present-day climate conditions. The unseen 40 °C extremes arise from joint occurrence of strong omega blocking with low soil moisture conditions in northern Europe. Our findings suggest that the Nordic countries should prepare for substantially higher peak temperatures than indicated by the historical observational record alone.