In May 2025, an extraordinary heatwave hit Iceland and eastern Greenland — the kind of event that stops scientists and ordinary residents in their tracks alike. On May 15, Egilsstaðir Airport recorded 26.6°C, a new national record for the month. It was one of many weather stations across the country logging temperatures as much as 13°C above the 1991 to 2020 average for that time of year.
The heatwave lasted around nine days. What set it apart wasn’t just how hot it got, but when it happened and how broadly it was felt. Iceland has always had unpredictable weather, but the scale and duration of this one prompted serious questions.
An international group of scientists from the World Weather Attribution initiative took a close look at what drove the event. The team included experts from the Icelandic Meteorological Office, alongside institutions in the Netherlands, Denmark, Sweden, the United Kingdom, and the United States. Their focus was the seven hottest days of May, and what they found was striking.
Climate change made this heatwave roughly 40 times more likely to occur and, on average, three degrees Celsius hotter than it would have been in a pre-industrial climate. There is always some uncertainty baked into these estimates, but the direction of the science is unambiguous: human-induced warming made this event substantially more probable and more intense.
The assessment drew on comparisons between observed temperatures and climate model outputs. Those models point to something worth sitting with: if global warming reaches 2.6°C later this century, heatwaves of this scale could occur at least twice as often and run, on average, two degrees warmer than what we experienced this May.
Right now, with roughly 1.3°C of warming since pre-industrial times, an event like this carries about a 1% annual chance of happening — once a century, in rough terms. In a cooler, pre-industrial world, a heatwave of this severity over Iceland would have been almost unheard of.
The complete analysis from World Weather Attribution is accessible here.
For additional details on the May heatwave in Iceland, click here.
