Heat waves are taking their toll as the weather changes: they last longer, get more frequent, and just get hotter. A question many people ask is, “When will it get too hot for normal daily activity as we know it, even for healthy young adults?”
The answer goes beyond the temperature you see on the thermometer. It’s also about humidity. Our search shows that the combination of the two can become dangerous more quickly than scientists previously believed.
Scientists and other observers have been alarmed by the increasing frequency of extreme heat coupled with high humidity, measured as “wet bulb temperature”. During the heat waves that hit South Asia in May and June 2022, Jacobabad, Pakistan, recorded a maximum wet-bulb temperature of 33.6 C (92.5 F) and surpassed it in Delhi, near the threshold. theoretical superior of human adaptability to humid heat.
People often point to a study published in 2010 who estimated that a wet-bulb temperature of 35°C, equivalent to 95F at 100% humidity, or 115F at 50% humidity, would be the safe upper limit beyond which the human body can no longer cool down by evaporating sweat. of the body. surface to keep the body’s core temperature stable.
It wasn’t until recently that this limit was tested on humans in laboratory settings. The results of these tests show an even greater cause for concern.
The PSU HEAT project
To answer the question “how hot is too hot?” We brought young, healthy men and women to Pennsylvania State University’s Noll Laboratory to experience heat stress in a controlled environment.
These experiments provide insights into which combinations of temperature and humidity begin to be harmful to even the healthiest humans.
Each participant ingested a small telemetry pill, which monitored deep or core body temperature. They then sat in an environmental chamber, moving just enough to simulate minimal activities of daily living such as cooking and eating. The researchers slowly increased the temperature in the chamber or the humidity and monitored when the subject’s core temperature began to rise.
This combination of temperature and humidity at which a person’s core temperature begins to rise is called the “critical environmental threshold.” Below these limits, the body can maintain a relatively stable core temperature over time. Above these limits, core temperature increases continuously and the risk of heat-related illness increases with prolonged exposures.
When the body overheats, the heart has to work harder to pump blood flow to the skin to dissipate heat, and when you sweat too, your body fluids decrease. In the most severe case, prolonged exposure can lead to heat stroke, a life-threatening condition that requires immediate and rapid cooling and medical treatment.
Our studies of healthy young men and women show that this upper environmental limit is even lower than the theoretical 35°C. It’s more like a wet bulb temperature of 31 C (88 F). This would equate to 31 C at 100% humidity or 38 C (100 F) at 60% humidity.
Dry environments vs. damp
Current heat waves around the world are approaching, if not exceeding, these limits.
In hot, dry environments, critical environmental limits are not defined by wet bulb temperatures, because nearly all of the sweat the body produces evaporates, which cools the body. However, the amount humans can sweat is limited, and we also get more heat from higher air temperatures.
Note that these limits are only based on keeping your body temperature from rising too high. Even the lowest temperatures and humidity can put pressure on the heart and other body systems. And while eclipsing those limits isn’t necessarily a worst-case scenario, prolonged exposure can become dire for vulnerable populations like the elderly and people with chronic illnesses.
Our experimental approach has now focused on testing older men and women, as even healthy aging makes people less tolerant of heat. Adding in the increased prevalence of heart disease, respiratory problems, and other health problems, as well as certain medications, can put them at even greater risk of harm. People over the age of 65 account for between 80% and 90% of victims of hot flashes.
How to stay safe during heat waves
Staying well hydrated and finding areas to cool off, even for short periods, is important in very hot climates.
While more cities are expanding cooling centers to help people escape the heat, there will still be many people facing these dangerous conditions with no way to cool off.
Even those with access to air conditioning they may not turn it on due to high energy costs, a common occurrence in Phoenix, Arizona, or due to large-scale power outages during heat waves or wildfires, as is becoming more common in the West.
A recent study focused heat stress in africa found that future climates will not be conducive to the use of low-cost cooling systems such as “swamp coolers” as tropical and coastal parts of Africa become wetter. Requiring much less energy than air conditioners, these devices use a fan to recirculate air through a cool, wet cushion to lower the air temperature, but become ineffective at high wet-bulb temperatures above 21°C (70°C). F).
All in all, evidence continues to mount that climate change is not just a problem for the future. It is one that humanity is currently facing and must face head on.
This article was written by a team of experts from Pennsylvania State University in the United States. It is republished from The Conversation under a Creative Commons license. Article in English