The high temperatures during tropical nights, which this summer are disrupting sleep, may only be a sign of what is expected to happen in the coming decades.
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A study published in the scientific journal Nature Climate Change warns that if greenhouse gas emissions remain high, the global number of hours with extreme heat could be four times higher by 2100. In this case, people could face on average up to four additional hours of heat each day.
The research was carried out by researchers from Sun Yat-sen University in Guangzhou, China, who examined hour-by-hour temperatures for the period 1981-2023.
To reach these conclusions, the team combined meteorological observation data with model estimates and climate projections up to the end of this century.
The analysis shows that heat increases have been recorded on more than 80% of the planet’s land surface. Over the period examined, the average increase was 62 hours of extreme heat per decade.
The data also highlight another worrying element: about 28% of the extreme heat episodes occurred on days that, based on the average daily temperature, were not considered hot.
In the scenario where greenhouse gas emissions remain high, during the years 2070-2099 a hot day could have approximately four more hours of extreme heat than at current levels.
Meanwhile, even days that do not fall into the category of hot days could contain about three additional hours of extreme temperatures.
According to the study’s predictions, population exposure to extreme heat could reach up to six times today’s level.
The greatest consequences are expected to be experienced by younger generations, especially people living in low- and middle-income countries. Over their lifetimes, they could be exposed to extreme temperatures much more than previous generations.
Scientists emphasize that the risk is determined not only by the maximum temperature, but also by the length of time the body remains exposed to it.
Dino Zardi, professor of Atmospheric Physics and Climate at the University of Trento, explains that humans have adapted to live within certain limits of temperature and humidity. According to him, when environmental conditions push them out of this comfort zone, biorhythms can be disrupted, even seriously.
He emphasizes that the disturbance caused in the body depends not only on the levels reached by temperature and humidity, but also on the duration of these conditions.
Thermal stress weakens the body’s ability to recover. For this reason, average daily temperatures may not be sufficient to measure the real impact of the heat experienced by people at different times, both during the day and at night.
The Mediterranean ranks among the most at-risk areas.
Zardi describes the study as an “alarm bell,” but at the same time notes that global climate models continue to have limitations in presenting local-level details.
Due to the relatively low spatial resolution, global simulations cannot accurately reproduce all the features of the land surface.
These characteristics directly influence the heat exchange between the ground and the atmosphere, and consequently, the daily temperature cycle.
Experts call for more detailed analyses to be developed in regions where warming is progressing faster.
Special attention is needed in the Mediterranean basin, in mountainous areas, at polar glaciers, and in cities. In urban areas, the “urban heat island” effect can further raise temperatures.
The findings constitute another warning about the consequences of climate change: in the future, not only the hottest days may increase, but also the hours during which the human body will remain under the influence of extreme heat.
