Future heat extremes in Norway: An emerging hazard?

With rising global temperatures, extreme heat is expected to become more frequent worldwide. Although less severe compared to other parts of Europe, heat extremes are increasingly affecting countries with relatively cooler climates, such as Norway. The heatwave in July 2025 highlighted Norway's limited preparedness for addressing this kind of risk. It is therefore of interest to investigate the extent to which heat extremes represent an emerging hazard in the country.

Using the recently updated national climate projections for Norway, we analyze both historical and future trends in heat extremes within regions defined by climatologically consistent temperature patterns. These climate projections are dynamically downscaled from global simulations, and bias-adjusted using observational data. To quantify the frequency and intensity of heat extremes at global warming levels, we apply a non-stationary Generalized Extreme Value (GEV) model. This approach offers the advantage of tying the global climate to the local changes in heat extremes. Our analysis focuses on the expected intensities of 100-year heat extremes at different levels of global warming and under different emission scenarios. Specifically, we evaluate projections of daily minimum and maximum temperatures and assess heat events of different durations (e.g., 1-, 3-, 5-, 7-, and 14-day events). This includes examining both daytime heat extremes (high maximum temperatures) and nighttime events (high minimum temperatures). The key research questions driving our study are: (1) Do heat extremes intensities differ at the same global warming levels under different emission scenarios, and (2) at what level of global warming do "severe" heat extremes begin to emerge?

Initial results show that, as expected, all observations and climate models show an increasing trend in the intensity of a 100-yr event with rising global temperatures. However, the rate of increase with global warming level differs markedly between climate models. Furthermore, there is a slight but not systematic difference between climate projections with RCP45 and SSP3-7.0 emission scenarios. Moreover, climate projections generally show a weaker trend compared to observations. The difference becomes more pronounced for longer duration events. Thus, future projections may underestimate the increase in the intensity of heat extremes in Norway.