While we wait for DANA, the heat persists: what is the limit that we can endure and why is it less than we thought

The human being is a species with a great capacity to adapt to new environments and situations, including extreme temperatures. The problem comes when we want to know what the limits of our tolerance and adaptability are, especially when a significant part of humanity lives close to these limits.

Heat waves in the Iberian Peninsula.
Continental Spain has suffered a flurry of heat waves accompanied by a notable increase in mortality, much higher than expected. So far in 2022, according to data provided by the Carlos III Health Institute, the excess mortality attributable to temperatures has been almost 4,800 people. Of these, 3,767 have corresponded to the period between May 1 and now. The situation is similar in Portugal and other places in the world.

Effects of heat on health.
That heat poses health risks is nothing new. Heat stroke can even kill us and is especially dangerous for the very young and the very old. Dehydration can also wreak havoc on the kidneys and heart. Tiredness is another of the less serious effects (not always) of heat, but it can also be a burden in our daily lives.

Heat can also affect us on a psychological level. In this sense, it can increase our aggressiveness and also reduce our ability to concentrate. Added to the tiredness caused by loss of sleep, our productivity also decreases.

A difficult question to answer.
As usual in science, this is not an easy question to answer. There is no maximum temperature at which our body shuts down, or a specific time that our body can endure. Our capacity varies a lot from person to person, and not only temperature and time affect, but also, for example, humidity.

Humidity is closely related to our ability to resist heat, since one of our main internal mechanisms to regulate our temperature depends precisely on water: sweat.

Approach the limit.
In recent years, a measure based on scientific studies that has been established as the limit of human endurance, the point at which the body cannot regulate its temperature, is the equivalent of a temperature of 35 degrees Celsius at 100% humidity . This would correspond to a heat index of around 70 according to the equivalences used by the State Meteorological Agency, AEMET. It is likely that the “real world” limit could be well below that.

For AEMET, the extreme danger begins at a heat index of 54. Reaching 40 degrees in a situation of 50% humidity could be enough to reach this level. We would also top it at 35 degrees with 80% relative humidity.

Analyze the heat we spend.
Various studies have tried to better understand what our limit is. Between 2013 and 2016, for example, one study looked at the body temperature and other variables of up to 300 wildland firefighters in the United States.

In addition to their work equipment, the participants carried out their work with a device that recorded their skin temperature, heart rate, inhaled carbon dioxide… The study found that physical work had a greater role than expected in firefighters, while that the opposite was true for the external temperature.

Another analysis, this one carried out in a controlled environment, studied how temperatures and effort affected the thermal stress of the participants, estimating this time that this was where the high temperatures were most suffered, but it would not be long before the first of many heat waves that we have this year.

Although in Europe the winter months leave a higher mortality, in recent decades we have seen several heat waves with tens of thousands of deaths. An example of this was the heat waves of 2003, which left more than 20,000 dead in Europe; or that of 2010 in Russia, with an excess mortality of 11,000 people.

Ways to avoid the worst of the heat.
For now, one of the most striking proposals this summer has been to name heat waves. Seville has been a forerunner in this, but the idea did not come from the municipal authorities, but had already come a long way.

Some experts believe that this measure can help raise public awareness of the danger of heat waves, but recommendations are usually based on individual behavior, such as avoiding exercise and direct sunlight in the middle of the day, wearing appropriate clothing and drink plenty of water.

The need to live with the heat is not new in Spain, but this summer of extreme heat and drought is serving to give us an idea of ​​what the future may be. There is still much to learn if we want to avoid the worst consequences of rising temperatures and aridification that we could experience in the coming years.