Danger from heat waves: At what temperature does it become deadly?

During heat waves, the human body reaches its limits.

Danger from heat waves: At what temperature does it become deadly?

During heat waves, the human body reaches its limits. But at what temperature does it become life-threatening even for healthy people? Another factor has a decisive influence on this - only through it does heat become a deadly danger.

Climate change is also causing temperatures to rise in Germany. Most recently, the country was hit by hot summers and new highs in 2018 and 2019. The current temperature record is now 41.2 degrees. Climate change is likely to bring further highs in the future. What is the maximum temperature that a healthy person can withstand?

In order to survive, humans have to keep their body temperature at 37 degrees Celsius, on the skin it is around 33 to 34 degrees. If the temperature rises above that permanently, it becomes life-threatening. What value does the thermometer have to show for this? That all depends. Under certain circumstances, 35 degrees air temperature can be deadly after a few hours. But under other circumstances, it is easy to live at 50 degrees.

The decisive factor here: the humidity. The lower it is, the higher temperatures people can endure. Because our body can then use a trick that cools the body down sufficiently: it sweats. The sweat evaporates on the skin, which creates a pleasant evaporative cooling effect. High temperatures are therefore not a problem in the dry desert air. But the higher the humidity, the worse this natural air conditioning system works. In tropical areas with very high humidity, temperatures in the 30s are unbearable.

From what combination of air temperature and humidity does it become dangerous? The cooling limit temperature can be derived from both factors - it is caused by the evaporation of sweat on the skin. The body can only give off enough heat to the environment if the cooling limit temperature is well below the skin temperature. This is no longer possible above a certain value - the climate researchers Steven Sherwood and Matthew Huber set this at 35 degrees in 2010.

This means that even if a perfectly healthy person stays in the shade under these conditions and has unlimited water available, they will die of overheating after a few hours. A study from spring 2022 found an even lower threshold of around 31 degrees in tests with young, healthy test subjects. For older people, who are more susceptible to heat, it may be even lower, the authors wrote.

But how do you know which cool limit temperature is approaching on a hot day? A very convenient solution is the online calculator Omnicalculator. Any values ​​for air temperature and humidity can be entered there, from which the cooling limit temperature is determined. Conveniently, the computer warns the user immediately if the result is in the critical range.

And that's reassuring: So far, potentially lethal cold-limit temperatures have only been measured in certain subtropical regions of the world, and then never for more than one to two hours. So far, India and Pakistan, the Middle East and the southwestern coastal areas of North America have been affected, according to an analysis of weather data from 1979 to 2017. However, experts assume that the duration and frequency of these heat dead zones will increase with climate change.

But even in Germany, heat can become a deadly danger for people. The number of heat-related deaths per year varies between a few hundred and many thousands. In this country, older people, the chronically ill and small children, who are particularly sensitive to high temperatures, are particularly at risk. However, biometeorologist Andreas Matzarakis emphasizes to ntv.de that everyone should take precautionary measures in the event of a heat warning from the German Weather Service (DWD). "It's a situation that affects everyone."

Heat warnings are issued by the DWD if severe heat stress is forecast for at least two days in a row. How should one behave then? Avoid the blazing sun, drink plenty of fluids and eat lightly, says Matzarakis, who heads the DWD Center for Medical Meteorological Research in Freiburg. "Some make the mistake of eating heavy food in the beer garden when the temperature is high. However, the body has to expend more energy, which also increases the body temperature."

Activities such as jogging should also be avoided when it is hot and indoor spaces should be kept cool by darkening. You should only ventilate when it is cooler outside than inside. "And pay attention to those around you," Matzarakis recommends. Everyone should keep an eye on elderly neighbors - and get medical help in emergencies.

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