When we talk about heat waves, attention almost always focuses on maximum temperatures. The 38, 40 or even 42 degrees recorded during the day end up in the headlines and in weather warnings. Yet experts warn that one of the most worrying phenomena is often invisible: the heat that doesn’t go away even after sunset.
In fact, in many Italian and European cities, night temperatures increasingly remain above 20°C. It is the phenomenon of the so-called tropical nights, an expression which until a few years ago evoked distant climates and which today increasingly describes Mediterranean summers.
According to the European climate change service Copernicus, a tropical night occurs when the minimum temperature does not fall below 20°C. A phenomenon that in recent decades has become increasingly frequent and intense in numerous European regions, especially in urban and coastal areas.
Why tropical nights worry experts
The problem is not just the discomfort of tossing and turning in bed without being able to fall asleep.
During the night our body should naturally lower its internal temperature. This process is fundamental for physical and mental recovery and allows the body to “reset” the stress accumulated during the day.
However, when the heat persists even at night, the cooling mechanism becomes less effective. The body continues to work to shed heat and the cardiovascular system remains under pressure longer.
The experts interviewed by Euronews on the occasion of the current heat wave affecting Europe explain that the lack of night-time cooling represents one of the most critical factors for public health, because it prevents the body from fully recovering from the thermal stress accumulated during the day.
For this reason, many people wake up tired even after sleeping for several hours. It’s not just a matter of interrupted sleep: the body simply cannot complete its recovery process.
Cities are the hardest hit
Tropical nights affect everyone, but not everywhere in the same way. In urban areas the phenomenon is amplified by the effect known as urban heat island. Asphalt, concrete and buildings absorb energy during the day and slowly release it in the following hours, keeping temperatures high even after sunset.
This is why in many cities the difference compared to the surrounding countryside can be notable. While in rural areas the temperature manages to decrease significantly during the night, in urban centers the heat remains trapped between buildings and streets.
The effects are also visible in daily life: open windows that bring no relief, apartments that cannot cool down and people forced to resort to fans and air conditioners more and more often.
A phenomenon destined to grow
Tropical nights are considered by scientists to be one of the most obvious indicators of climate change.
According to Copernicus, the increase in average global temperatures is increasing not only the number of very hot days, but also the number of exceptionally mild nights. In other words, we are not only seeing hotter afternoons, but also the progressive disappearance of the cool hours that traditionally offered a break from the summer heat.
The current heat wave affecting much of Europe confirms this trend. From the Iberian Peninsula to Italy, passing through France and the Balkans, numerous areas are recording high night temperatures for several consecutive days.
It’s not just a question of comfort
The World Health Organization recalls that extreme heat represents one of the most significant climate risks for human health.
Elderly people, children, people with cardiovascular, respiratory or metabolic diseases are particularly vulnerable. When the heat continues even at night, the risk increases because the body loses the opportunity to recover between one hot day and another.
For this reason, experts advise not to underestimate the minimum temperatures. If the daytime peaks attract attention, it is often the tropical nights that best tell how the climate is changing.
The real sign of the new normality, in fact, may not be the thermometer that exceeds 40 degrees in the afternoon, but the one that stubbornly continues to remain above 25 at midnight.
