The longest and rarest heatwaves - which can last for weeks - show the greatest increase in frequency according to a new study by University of California, Los Angeles (UCLA).
The new study Accelerating increase in the duration of heatwaves under global warming published in the 7 July 2025 issue of the journal Nature Geoscience reveals that the longest heatwaves will see the greatest acceleration, and the frequency of the most extreme heatwaves will increase the most. The duration of a heatwave exacerbates the risk to people, animals, agriculture and ecosystems.
UCLA climate scientist and senior author of the study David Neelin said, “Impacts in tropical regions tend to be bigger than in temperate regions, and winter warm spells will change less than summer because summer tends to have smaller variability.
Professor Neelin said, “Southeast Asia and the equatorial regions of South America and Africa will likely see some of the greatest impacts. The research projected that heatwaves in equatorial Africa lasting more than 35 days would happen a whopping 60 times more often in the near future (2020 to 2044) compared with the recent past (1990 to 2014).”
The study found that not only will climate change make heatwaves hotter and longer, but the lengthening of heatwaves will accelerate with each additional fraction of a degree of warming.
Researchers led by UCLA and the Universidad Adolfo Ibañez in Santiago, Chile, found that the tropical regions will see larger changes than temperate regions, and summer heatwaves will lengthen more than winter warm spells.
Professor Neelin said future research in this area will need to evaluate how the longer heatwaves will affect variables like soil moisture and wildfire risk, which in turn will help inform critical adaptations for agricultural planning, utility sector strategies and urban planning from cooling centres to shade plantings.