Analysis: Climate change made the May heatwave more likely and more intense
In May 2025, an unusually intense heatwave affected Iceland and eastern Greenland. On 15 May, temperatures reached 26.6°C at Egilsstaðir Airport, setting a new national temperature record for the month of May. Temperature records were also broken at numerous other weather stations, with some locations experiencing temperatures up to 13°C above the monthly average for the period 1991–2020.
The heatwave lasted for around nine days, and although similar weather patterns have been observed before, this event stood out due to its unusually early timing, its duration, and its widespread impacts.
An international group of scientists within the World Weather Attribution initiative, including experts from the Icelandic Meteorological Office, the Netherlands, Denmark, Sweden, the United Kingdom, and the United States, has published an analysis of how human-induced climate change influenced this heatwave. The study focuses in particular on the seven hottest days in May in Iceland.
The results show that human-induced climate change made this heatwave around 40 times more likely and, on average, three degrees Celsius hotter than it would otherwise have been. While there is some uncertainty in such estimates, scientists conclude that there is a high probability that climate change both increased the likelihood of the event and amplified its intensity.
The analysis is based on a comparison between observed temperatures during the heatwave and results from climate models. These models also suggest that if global warming reaches 2.6°C later this century, heatwaves of this magnitude could become at least twice as common and, on average, two degrees Celsius hotter than they are today.
Under the current climate, which has already warmed by approximately 1.3°C since the pre-industrial era, such heatwaves are estimated to have a 1% chance of occurring each year, meaning they can be expected roughly once per century. In a cooler, pre-industrial climate, events of this magnitude would have been extremely rare or virtually unknown within Iceland's recorded history.
The full analysis from World Weather Attribution is available here
Further information on the May heatwave in Iceland can be found here
