As the climate changes, heat waves are becoming even more powerful. When will it get too hot for normal daily activity as we know it, even for young, healthy adults?
You can see the temperature on the thermometer, but it's not the answer. It's also about the temperature. Scientists previously believed that the combination of the two could be dangerous.
Scientists and other observers are concerned about the increasing occurrence of extreme heat and high humidity.
Jacobabad, Pakistan, had a maximum wet-bulb temperature of 33.6 C (92.5 F), which was close to the upper limit of human adaptation to humid heat.
A study published in 2010 said that a wet-bulb temperature of 35 C, equal to 95 F at 100 percent humidity, or 115 F at 50 percent humidity, would be the upper limit of safety, beyond which the human body can no longer cool itself by sweating.
The limit was tested on humans in laboratories. The tests show a bigger cause for worry.
Young, healthy men and women were brought to the Noll Laboratory at Penn State University to experience heat stress in a controlled environment in order to answer the question of how hot is too hot.
These experiments show which combinations of temperature and humidity can be harmful.
Each participant took a pill to monitor their core temperature. They sat in an environment that mimicked the minimal activities of daily life, such as cooking and eating. When the subject's core temperature began to rise, researchers increased the temperature in the chamber or the humidity.
The "critical environmental limit" is a combination of temperature and humidity that causes the core temperature to rise.
The body is able to keep a stable core temperature over time. The risk of heat-related illnesses with long-term exposure is increased if core temperature goes above those limits.
When the body gets too hot, the heart has to work harder to get blood to the skin so it doesn't get too warm. Immediate and rapid cooling and medical treatment are required if heat stroke is to be avoided.
Our studies show that the upper environmental limit is lower than we thought. It would be equivalent to 31 C at 100% humidity or 100 F at 60 percent humidity.
W. Larry Kenney has a CC by-ND.
Similar to the National Weather Service's heat index chart, this chart shows the combination of air temperature and relative humidity into critical environmental limits. The average critical environmental limit for young men and women is shown by the border between yellow and red.
The current heat waves are approaching the limits.
In hot, dry environments, the critical environmental limits aren't defined by wet-bulb temperatures, because almost all the sweat the body produces evaporates to cool the body. We gain more heat from the higher air temperatures because we can't sweat as much.
The cutoffs are based on keeping your body temperature from rising too much. Stress can be placed on the heart and other body systems.
Exposure may become dire for vulnerable populations such as the elderly and people with chronic diseases if the limits are not surpassed.
Older men and women are being tested because healthy aging makes them less heat tolerant. Adding on the increased prevalence of heart disease, respiratory problems and other health problems can put them at even higher risk of harm. The majority of heat wave casualties are people over the age of 65.
In high heat, it's important to stay hydrated and seek out areas to cool down.
More cities in the United States are opening cooling centers to help people escape the heat, but there will still be many people who won't be able to cool themselves off.
Even those with access to air conditioning might not turn it on because of the high cost of energy, which is a common occurrence in Phoenix, Arizona, and is becoming more common in the western US.
As the tropical and coastal parts of Africa become more humid, the use of low-cost cooling systems such as "swamp coolers" won't be a good idea.
These devices use a fan to recirculate the air across a wet pad to lower the air temperature, but they don't work well at high wet-bulb temperatures.
Climate change is more than just a problem for the future according to the evidence. It is a problem that humanity is currently facing.
Daniel Vecellio is a Geographer-climatologist at Penn State and Rachel Cottle is a student.
Under a Creative Commons license, this article is re-posted. The original article is worth a read.
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