The Heatwave: How Much Heat Can Humans Bear?

Given the records of temperature throughout the world it is imperative to anticipate the limits of heat and moisture that the human body can withstand. The international scientific term to measure this resistance capacity is the “wet bulb and globe temperature (TGBH)” (“Wet Bulb Globe Temperature” – WBGT in English), which combines the calculation of heat with the degree of humidity.

He “bulb” it is the mercury deposit of a traditional thermometer, wrapped in a damp cloth, whose evaporation serves to measure the humid temperature of the air. He “balloon” It is a hollow sphere painted black that, attached to a thermometer, is used to measure thermal radiation.

Experts estimate on average that a perfectly healthy young person will die within six hours of exposure to a TGBH temperature of 35ºC (95 degrees Fahrenheit). That temperature is equivalent to 35°C of dry heat and 100% humidity, or 46°C with a fifty% moisture.

At that critical point, sweat, the body’s main tool for lowering your core temperature, fails to evaporate from the skin, eventually leading to heat stroke, internal organ collapse, and death.

Only a TGBH of 35°C a dozen times, mainly in South Asia and the Persian Gulf, Colin Raymond of NASA’s Jet Propulsion Laboratory told AFP.

None of those cases lasted more than two hours, meaning there have never been “mass mortality phenomena” linked to this limit of human survival, said Raymond, author of a large study on the subject. But extreme heat doesn’t need to get anywhere near that level to kill a person.

Most common episodes

In fact, everyone has a different threshold based on their age, health, and other social and economic factors, experts say. For example, it is estimated that more than 61,000 people died due to last summer’s heat in Europe, where there is rarely enough humidity to create “wet bulb temperatures” dangerous.

But as temperatures continue to rise (July was the warmest on record), scientists warn that TBGB episodes will also become more common.

The frequency of such events has at least doubled in the last 40 years, explains Raymond, who sees the increase as a serious consequence of human-caused climate change.

Raymond calculates that wet bulb temperatures “will regularly overcome” 35°C in various parts of the world in the coming decades if the world warms 2.5°C above pre-industrial levels.

To test this limit, researchers at the Pennsylvania Public University measured the core temperatures of young, healthy people inside a thermal chamber.

The participants reached their “critical environmental limit,” when their bodies could not stop their core temperature from rising further, to a TGBH of 30.6°C.

Joy Monteiro, a researcher in India who last month published a study in Nature looking at wet-bulb temperatures in South Asia, said most of the region’s deadly heat waves were well below the theoretical 35 threshold. °C

Human resistance to these temperatures is “tremendously different depending on each person”he told AFP.

The elderly, the most vulnerable

“We do not live in a vacuum, especially children”said Ayesha Kadir, a UK pediatrician and Save the Children health adviser. Young children are less able to regulate their body temperatures, putting them at greater risk, she said.

But it is the elderly, who have fewer sweat glands, who are the most vulnerable. almost the 90% of heat-related deaths in Europe last summer were among people aged 65 and over.

People who have to work outdoors in high temperatures are also at higher risk. Monteiro noted that people without access to toilets often drink less water, leading to dehydration.

Their research has shown that the El Niño weather phenomenon has raised the TGBH in the past. The current El Niño, the first in four years, is expected to peak at the end of this year.

Wet-bulb temperatures are also closely related to ocean surface temperatures, Raymond said.

The world’s oceans reached an all-time high temperature last week, surpassing the previous record set in 2016, according to the European Union’s climate observatory.

Source: AFP