Reevaluating Heat Survival Thresholds: The Case for a Lower…

Harvard researchers are questioning the 35°C wet-bulb temperature survival threshold, suggesting it may actually be around 31°C. This insight arises from recent physiological studies and discussions concerning heat stress, particularly affecting vulnerable populations in the Global South. Emphasis is placed on understanding the complex impacts of heat exposure beyond mere survival, aiming for improved human livability in extreme temperatures.

Recent research from Harvard University has cast doubt on the widely accepted wet-bulb temperature survival threshold of 35°C, suggesting it might be as low as 31°C. This conclusion emerged during discussions at an interdisciplinary conference held in Delhi aimed at addressing heat stress in India and exploring adaptation strategies.

Wet-bulb temperature is a crucial metric that combines heat and humidity to indicate how well humans can cool themselves through sweating. As the wet-bulb temperature approaches skin temperature, sweat evaporation ceases, undermining the body’s cooling mechanisms. The threshold that necessitates emergency responses during extreme heat is significantly more complex than previously understood, according to the researchers.

The original 35°C threshold was proposed in 2010 by scientists at the University of New South Wales. They theorized that prolonged exposure at this temperature could lead to heat stroke within six hours. However, contemporary studies indicate a lower survival limit. A study from Pennsylvania State University in 2023 showed that even healthy individuals could develop uncompensable heat stress at a wet-bulb temperature of roughly 31°C after six hours of exposure.

Further research from Penn State in 2022 revealed that the 35°C threshold overestimates conditions leading to heat stress. Their experiments found critical wet-bulb temperatures ranging from 25°C to 28°C in hot-dry environments, and from 30°C to 31°C in warm-humid environments. A comprehensive review of heat exposure studies from the University of Ottawa highlighted that even brief exposure to heat waves can result in elevated core body temperatures exceeding 38°C.

Dr. Satchit Balsari from Harvard Medical School highlights the lack of data regarding prolonged exposure to heat and humidity among at-risk populations in the Global South, suggesting that existing studies predominantly focus on Caucasian males and specific occupational groups. To address this gap, Balsari’s team is developing a personalized heat exposure index, akin to dosimeters used for measuring radiation exposure in medical professionals.

Dr. Robert Meade, a thermal physiologist, reiterated that the 35°C threshold is a theoretical figure. He noted that when skin temperature matches this level, sweating becomes ineffective as heat loss is hindered, risking rapid increases in body temperature. He emphasized that mortality during heat waves often results from conditions like heart attacks and kidney injuries rather than elevated body temperatures alone.

Balsari also stressed the need to prioritize human well-being over mere survival, pointing to the negative impacts of extreme heat on daily life and work productivity. He provided an example of a street vendor who observed that her vegetables spoil at temperatures of 40-42°C, indicating that extreme heat conditions significantly affect livelihoods.

The Pennsylvania study warns that regions like the Middle East and the Indus River Valley may face dangerous heat extremes with only 1.5°C of warming compared to pre-industrial levels, potentially making living conditions untenable. Balsari cautioned against complacency regarding acclimatization, arguing that historical exposure to heat does not inherently confer resilience against rising temperatures.

The research presented by Harvard scientists urges a reevaluation of the wet-bulb temperature threshold for heat survival, suggesting it is lower than traditionally believed. With newer studies indicating 31°C as a critical threshold, a nuanced understanding of heat exposure is necessary, especially for vulnerable groups in the Global South. Emphasizing overall well-being rather than mere endurance in high temperatures is crucial for developing effective heat adaptation strategies.

Original Source: www.hindustantimes.com