Hot weather, not just in summer: here’s why heatwaves are now possible in autumn and spring too
According to a study led by NASA’s Goddard Institute for Space Studies (GISS), climate change is causing extreme heatwaves to occur with increasing frequency, even outside the season in which they usually occur
Key points
Although summer is drawing to a close, we may still have to contend with occasional spells of extreme heat. With bad weather setting in across much of the peninsula, yet another heatwave of the year has come to an end, and the record temperatures recorded in recent days have fallen sharply: on Saturday 12 September, all 27 cities monitored by the Ministry of Health will be marked with a green sticker. However, according to a study led by NASA’s Goddard Institute for Space Studies (GISS) and published in the journal AGU Advances, climate change is making abnormal heatwaves increasingly frequent, even outside the season in which they usually occur.
The study
Researchers at the GISS, led by Catherine Ivanovich, based their study on a detailed comparison between extreme heat events recorded between 1980 and 1989 and those occurring during the period 2015–2024. The results show that, over the last 45 years, heatwaves have expanded significantly across half of the world’s landmass in terms of dry heat, and across just under half (48 per cent) in terms of humid heat.
This expansion, however, has taken place asymmetrically: towards spring in some regions and towards autumn in others. Global warming, whilst not sufficient on its own to explain this asymmetry, is its main cause. However, based on the data collected, it is likely that other factors, such as changes in rainfall and land use, also play a part.
The results
As the study shows, episodes of abnormal heat are becoming more prolonged and are occurring unevenly across the globe. In Western Europe, Southern Africa and North-Western India, extreme temperatures are occurring increasingly earlier in the spring, whilst in Eastern Europe, the Western United States, Northern Africa and Eastern China, these events are becoming more frequent during the autumn months.
The study takes the city of Phoenix, the capital of Arizona in the United States, as an example. Here, 183 days of extreme heat were recorded between 1980 and 1989, and 338 between 2015 and 2024. Whilst none of the events in the 1980s occurred after the end of the hot season, 6 per cent of those in the second decade under review occurred after that period. The researchers’ analysis shows that the median date for dry heatwaves in the city has shifted forward by 10 days, whilst that for humid heatwaves has shifted forward by 5.5 days.
