In May 2025, Iceland and eastern Greenland experienced an unprecedented heatwave that shattered temperature records. On May 15, Egilsstaðir Airport recorded a sweltering 26.6°C, marking the highest temperature ever logged in Iceland for that month. Numerous weather stations across the region reported similar extremes, with some areas reaching temperatures up to 13°C above the monthly average calculated from 1991 to 2020.
This extraordinary heatwave persisted for about nine days. While Iceland has seen similar weather patterns in the past, this event was notable not just for its intensity but also for its early arrival and widespread repercussions.
An international coalition of scientists associated with the World Weather Attribution initiative, which includes experts from the Icelandic Meteorological Office and institutions in the Netherlands, Denmark, Sweden, the United Kingdom, and the United States, has assessed the role of human-induced climate change in this unusual weather phenomenon. Their analysis zeroes in on the seven hottest days in May across Iceland.
The findings reveal striking evidence that climate change has made this heatwave approximately 40 times more likely, raising temperatures by an average of three degrees Celsius more than would have been the case in a pre-industrial climate. Although some uncertainty surrounds these estimates, scientists are confident that climate change has both heightened the likelihood of such events and intensified their severity.
This analysis involved comparing actual temperatures recorded during the heatwave with outputs from climate models. The models indicate that if global warming escalates to 2.6°C by the end of this century, heatwaves of this magnitude could become at least twice as frequent and, on average, two degrees Celsius hotter than today’s temperatures.
Currently, with the climate already warmed by about 1.3°C since the pre-industrial era, heatwaves of this nature have about a one percent chance of occurring each year, suggesting such events could be expected roughly once a century. In a cooler, pre-industrial climate, occurrences of this scale were exceedingly rare—or possibly even unknown—in Iceland’s recorded history.
The full analysis from World Weather Attribution is available here.
Further details regarding the May heatwave in Iceland can be found here.