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Escalating Heatwave Threat in the US Sparks Urgent Concerns Over Human Survival Limits

Escalating Heatwave Threat in the US Sparks Urgent Concerns Over Human Survival Limits | Credits: Shutterstock

United States: Record-shattering heatwaves have enveloped the US mere weeks into summer, with at least 38 suspected fatalities attributed to heat-related diseases thus far.

Climate change is propelling unprecedented heat extremes, prompting researchers to urgently investigate the survival temperature limits for humans without air conditioning and the imminent potential for regions to reach deadly heat levels.

Scientists are increasingly alarmed that an extensive heatwave striking an area lacking reliable air conditioning could precipitate a mass mortality event. Recent studies reveal that the survival threshold for heat is significantly lower than previously estimated, especially for the elderly and those in arid climates.

“We possess a limited capacity to perspire, with older individuals having an even lesser ability,” remarked Jennifer Vanos, an associate professor in the School of Sustainability at Arizona State University.

“In the US, heat-related deaths should be entirely preventable with access to air conditioning. However, in many parts of the world, such facilities are non-existent.”

Key Insights:

Maintaining Core Temperature:

Experts urge humans to maintain the necessary core temperature. Accordingly, the human body cannot bear if the internal body temperature reaches up to 43 degrees Celsius, which is around 109.4 degrees Fahrenheit.

“Reaching this core temperature would result in a 99.9% mortality rate,” Vanos explained.

This represents the extreme survival limit. Heat typically claims lives in more insidious ways, such as exacerbating pre-existing conditions like cardiovascular or renal diseases.

The Crucial Role of Humidity:

The fact has been explained by a climate scientist and professor of atmospheric science at Colorado State University – Scott Denning, who outlined that excessive humidity hinders sweat evaporation, preventing the skin’s surface from cooling below the internal body temperature.

“This leads to metabolic heat accumulation, causing severe fever, heat stroke, and death,” Denning was further quoted saying.

Wet-Bulb Temperature:

Wet bulb temperature is a metric that is used by scientists to measure the combined effects of heat and humidity. In this process, the temperature is measured with the help of a thermometer, which is enveloped in a moist cloth.

“The wet-bulb temperature must be slightly cooler than the body’s interior,” Denning noted. Otherwise, heat dissipation from the body is impeded.

A Pivotal Benchmark:

Following a landmark 2010 study, climate researchers frequently use a wet-bulb temperature of 35 degrees Celsius—roughly 95 degrees Fahrenheit at 100% humidity—as the upper limit for human survival without cooling measures.

However, this benchmark does not account for factors like sunlight exposure, clothing, and physical activity.

Approaching the Threshold:

A 2020 study revealed that instances of extremely humid heat have doubled since 1979, with regions including coastal India, Pakistan, the Persian Gulf, and the Gulf of Mexico nearing the wet-bulb threshold. Two locations briefly surpassed it.

Denning expressed concern about potential mass mortality events in these regions as global temperatures continue to climb.

“In densely populated urban areas along the Arabian Sea and Indian Ocean, hundreds of millions of people lack air conditioning,” he warned.

Underestimated Dangers:

Emerging research suggests that previously assumed upper limits are overly optimistic.

A 2022 study published in the Journal of Applied Physiology, based on heat chamber test data, posits that the wet-bulb temperature threshold is likely closer to 30-31 degrees Celsius (86-87.8 degrees Fahrenheit) for “young, healthy” individuals performing basic life activities.

Dry Heat Risks, Especially for the Elderly:

Vanos emphasized that individual survival limits vary, with age being a critical factor.

Her research, published in Nature Communications last winter, indicates that physiological thresholds for heat stroke are considerably lower than previously understood, particularly in dry heat conditions.

The study suggests that most older adults, who perspire less efficiently, face severe risks if exposed for six hours to temperatures exceeding 115 degrees Fahrenheit, even with low humidity and shade.

“There is no single threshold for survivability, and assuming otherwise is perilous,” Vanos cautioned.

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