The World Health Organisation (WHO), along with health and climate experts, have warned that extended heatwaves are no longer a temporary inconvenience, but a growing threat to human health that can be fatal, amid record-breaking heat raising serious questions about cumulative effects.
According to Agence France-Presse (AFP), the greatest danger lies not only in immediate impacts such as heatstroke or severe dehydration, but also in the aggravation of chronic illnesses such as heart and respiratory diseases, whose symptoms may appear or lead to death several days after the start of a heatwave. French Health Minister Catherine Vautrin said that the effects of heat on the body do not necessarily appear immediately, urging vigilance in the days that follow.
Although scientific debate continues over the extent of cumulative impacts — with a 2011 study in Epidemiology pointing to a “slight additional effect” after the fourth day, and a 2018 Science of the Total Environment study downplaying the role of duration — more recent research has revealed new dimensions of risk. Scientific reports published in 2024 in The Lancet Countdown and Sleep Medicine described rising temperatures as a “global threat to sleep”, impairing the body’s ability to recover.
These findings recall the summer of 2003, when an extended heatwave in Europe caused more than 70,000 deaths, underscoring the importance of studying this phenomenon in the context of accelerating climate change.
