As climate change leads to rising global temperatures, the occurrence of extreme heat is increasing, thereby posing a greater health risk. While the human body demonstrates remarkable resilience, it has its limits. This raises the question: what is the maximum temperature that individuals can withstand?
The typical human body temperature is not a fixed figure but rather a range, often approximated at 37°C (98.6°F), although individual baseline temperatures can differ. This temperature varies throughout the day and is influenced by factors such as age, physical activity, and the measurement technique employed. A temperature exceeding 38°C (100.4°F) is typically regarded as a fever, suggesting that the body may be combating an illness.
Colin Raymond, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory specializing in extreme heat, noted that if humidity is low while temperatures are high, or the opposite, the wet-bulb temperature is unlikely to approach the critical threshold for the human body. However, when both humidity and temperature are elevated, the wet-bulb temperature can approach perilous levels.
For instance, when the air temperature reaches 115°F (46.1°C) with a relative humidity of 30%, the wet-bulb temperature is approximately 87°F (30.5°C). Conversely, when the air temperature is 102°F (38.9°C) and the relative humidity is 77%, the wet-bulb temperature rises to about 95°F (35°C), which is considered the ‘danger zone’ for humans. The inability of individuals to survive in conditions of extreme heat and humidity stems from their compromised capacity to regulate internal body temperature.
A wet-bulb temperature of 95°F does not lead to immediate death; however, according to Raymond, it likely takes approximately 3 hours for such heat to be fatal. He noted that there is no definitive way to ascertain the precise duration, as some research has attempted to estimate it, but it is unethical to expose humans to such elevated temperatures for extended periods.
Additionally, there is no method to verify that 95°F is the precise wet-bulb temperature that is lethal. Raymond approximated that the actual figure lies within the range of 93.2°F to 97.7°F (34°C to 36.5°C).
Risk of unlivable temperatures
Air conditioning can save people from unlivable heat — but not all people have access to it, and Air conditioning provides relief from unbearable heat; however, not everyone has access to it, and even in areas where many individuals do have air conditioning, the electrical grid may be inconsistent, as noted by Raymond.
A few locations have recorded a wet-bulb temperature of 95 F throughout history, according to a study published in Science Advances, although these instances have only occurred for brief durations. Since the late 1980s and 1990s, regions such as the Indus River Valley in central and northern Pakistan and the southern coast of the Persian Gulf have been identified as hotspots.
“Certain areas are already beginning to experience these conditions for an hour or two,” Raymond remarked. “With global warming, this occurrence will only become more common.” He further indicated that regions likely to face these temperatures in the next 30 to 50 years include northwest Mexico, northern India, Southeast Asia, and West Africa.
“Regrettably, due to the climate change that is already set in motion, we will continue to experience significant warming, even if we cease greenhouse gas emissions today,” Raymond stated. “It seems unavoidable that the regions I mentioned will be contending with this challenge for the foreseeable future, and I hope that additional areas do not join that list.”
Risk of disease
Some researchers contend that the 95 F wet-bulb threshold may actually downplay the risks associated with high temperatures on human health.
Pope Moseley, a researcher at Arizona State University specializing in heat-related illnesses, warns that this figure pertains to the maximum temperature a person can endure under ideal conditions. In reality, various factors such as age, physical fitness, specific medications, and existing health conditions can all restrict an individual’s capacity to manage heat, even at lower temperatures.
For example, engaging in physical activity and being exposed to direct sunlight can increase the likelihood of overheating at lower temperatures. Older adults, individuals with certain health issues like hormonal disorders or obesity, and those taking antipsychotic medications may struggle to regulate their body temperature effectively, making them more susceptible to heat-related fatalities.
Elevated temperatures can exacerbate numerous health conditions; for instance, heat can intensify high blood pressure and various cardiac problems, as it influences the narrowing of blood vessels. Individuals suffering from kidney disease face heightened risks in hot weather due to its effect on fluid balance, which must be meticulously managed by those with kidney issues. Additionally, certain severe psychiatric disorders may impair an individual’s capacity to identify the initial symptoms of heat stress, thereby endangering them during heat waves. Other health conditions that may deteriorate due to heat include diabetes, asthma, and dementia.
Source: Live Science
The article is edited by Md. Rafikul Islam, Agriculturist, Science writer and Co-founder, Biology School.
