Scientists have unveiled the critical threshold of heat and humidity the human body can endure.
A man drinks water at a fountain in Xativa, south of Valencia, on August 10, 2023 as the country faces the third heatwave of the summer with 44,6 ºC registered in Sevilla and nearly 47ºC in Valencia region
'Wet Bulb Temperature'
According to AFP, new research shows the limit, known as the "wet bulb temperature," representing the maximum combination of heat and humidity before sweat no longer evaporates from the skin, leading to heatstroke, organ failure, and death.
While this threshold occurs at around 35 degrees Celsius (95 Fahrenheit), recent research suggests it could be even lower.
Colin Raymond from NASA's Jet Propulsion Laboratory said the wet bulb limit of human survival has been breached only around a dozen times, primarily in South Asia and the Persian Gulf.
Although none of these occurrences extended beyond two hours, they effectively averted widespread mortality events associated with this critical threshold.
Nonetheless, specialists stress that fatalities resulting from intense heat are feasible even at less severe levels. Factors such as age, health, and socio-economic circumstances play a role in determining an individual's susceptibility.
In Europe last summer, for instance, more than 61,000 fatalities were linked to heat, even in regions where the perilous wet bulb temperature range is seldom attained.
Scientists warn that dangerous wet bulb events will become more frequent as global temperatures continue to rise. The frequency of such events has doubled over the last four decades, driven by human-caused climate change.
'Critical Environmental Limit'
According to Raymond's research, wet bulb temperatures exceeding 35 degrees Celsius could become common worldwide if global temperatures rise by 2.5 degrees Celsius above pre-industrial levels.
To test the wet bulb limit, researchers at Pennsylvania State University evaluated young, healthy participants in a heat chamber. They found that the "critical environmental limit," where the body can't prevent further core temperature increase, was reached at 30.6 degrees Celsius wet bulb temperature, lower than previously theorized.
In the past, El Niño weather patterns have been known to elevate wet bulb temperatures. However, researchers emphasize the strong correlation between wet bulb temperatures and ocean surface temperatures.
Notably, the global oceans recently achieved an unprecedented peak temperature, surpassing the previous record established in 2016.
Scientists highlight the importance of investigating wet bulb temperatures to comprehend how climate change affects human survival, particularly for susceptible groups such as children, the elderly, and individuals laboring in high-temperature environments.
"Extreme heat is increasingly being acknowledged as a serious hazard to human health, through a combination of physiological responses to heat, expressed as dry and wet bulb temperatures, and personal factors," the study's abstract reads.
The research emphasizes that using physiological thresholds is a more reliable method to assess health impacts and suggests that wet bulb temperature alone is inadequate to indicate hazardous heat conditions.
In related news, NASA JPL unveiled a series of detailed maps showcasing the extent of land-surface temperature variations in Phoenix, Arizona, last July, a month marked by an unprecedented heat wave.
The maps depict how urban landscapes, including streets, buildings, and airport runways, retained heat even after sunset, contributing to the persistence of high temperatures.
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