The heat of death.. What is the degree of heat that the human body cannot withstand?
In conjunction with the heat wave currently taking place in France and Europe, the question returns about the body's abilities to withstand the rising heat waves due to climate change. Air humidity is a key factor in the effect of heat on humans by impeding the process of sweat secretion. To assess this, specialists measure the so-called wet-bulb temperature. Scientists expect the expansion of areas that may become uninhabitable due to warming and humidity. Detail with Rabih Osbrahim.
Temperatures and humidity reach levels beyond human tolerance
Extreme temperatures and humidity events are occurring now twice as high as they were 40 years ago.
Over the hundreds of thousands of years of our existence on Earth, modern humans have adapted to a huge variety of climates, from the arid heat of the Sahara to the icy cold of the Arctic. But we as human beings have our limits. If the temperature and humidity were high enough, even a healthy person, sitting still in the shade, and able to reach for water, would collapse under the heat.
As heat waves increase in temperature and frequency, research has suggested that some places will experience climate events in the coming decades that reach the limits of human temperature tolerance. But for now, a new study shows that this has already happened. The results, which were published inmagazine"Science Advances» Science Advances, on the need to rapidly reduce greenhouse gas emissions and put in place policies to help the most vulnerable populations maintain their normal body temperature.
High temperatures stimulate the human body to produce sweat, which in turn cools the skin when it evaporates. But when there is very high humidity in the atmosphere, this process of evaporation slows down and eventually stops. This stage comes when the so-called wet bulb temperature - a measure that combines air temperature and humidity - is reached, which is 35 degrees Celsius (95 degrees Fahrenheit).
Previous analyzes using climate models indicated that parts of the Persian Gulf region , the Indian subcontinent, and eastern China will experience heat waves on a regular basis, which will cause this limit to be breached later in the century. But the authors of these studies looked in large areas over different time zones, and found that this would mask more local temperature rises of shorter duration, in very harsh climatic conditions. To see what other researchers might be missing, Colin Raymond, who conducted the new study as a Ph.D. student at Columbia University, says, "We decided to look at the image more closely."
Raymond and his colleagues examined temperature data from more than 7,000 weather stations around the world, some of which dated back to 1979. They found that the intense moist heat is now occurring about twice as much as it was four decades ago, and that the intensity of that heat is about twice as high as it did four decades ago. is increasing. In many places, wet bulb temperatures reached 31 degrees Celsius or higher. Several places have recorded readings above the critical mark of 35°C. Determining this pattern is “important because it is based on weather station data, which is the most direct evidence we usually have,” says MIT climatologist El-Fateh Eltaher, who was not involved in the new research but has previously worked on the topic.
These wet temperature extremes have already appeared in the same places that previous modeling studies have identified as future hotspots. Most of them were coastal areas close to warm bodies of water, which could provide an abundance of moisture, and be exposed to high temperatures on land. In other regions, especially in the Indian subcontinent, which are regions where the monsoon begins with winds laden with moisture.
"It is possible that there will be higher values for the wet bulb," says Raymond, who is now at NASA's Jet Propulsion Laboratory. Temperatures usually reach their maximum levels for only an hour or two, so they haven't necessarily reached the limits of human endurance yet. But these events will take longer, and will cover larger areas in a warmer future. In addition, even much lower moist bulb temperatures can be fatal, particularly in the elderly or those with underlying health conditions. The historical heatwaves that killed thousands of people across most of Europe in 2003 and in Russia in 2010 did not record a temperature higher than 28°C on the wet bulb temperature scale. Al-Taher says:
The new paper also revealed that parts of the world would see a regular temperature rise of more than 35 degrees Celsius on the wet bulb scale if global average temperatures rose by just 2.5 degrees Celsius, exceeding the recorded climate. In the pre-industrial era. The world is already getting warmer by about 1 degree Celsius above that level. "This kind of weather event can become regular with the temperature not rising much more than we've seen," says Christina Dahl, chief climate scientist at the Union of Concerned Scientists, who was also not involved in the study.
This prediction highlights our need to urgently reduce greenhouse gas emissions to limit global warming as much as possible, which in turn will reduce the number of such events occurring in the future. It also raises many questions, including the policies that governments will need to put in place to protect vulnerable groups, such as setting up cooling centers for elderly populations or sending out warnings ahead of heat waves. Industries whose workers work outdoors — such as agriculture and construction — may need to shift their work schedules to times when the weather is cooler during the day. Even in the United States, where air conditioning is plentiful, more heat now kills more people than cold, floods, or hurricanes.
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