Hot and humid weather is quite possibly the worst weather, as most people will feel sticky and uncomfortable, to the point that it will affect their mood and ability to think. This combination is so terrible that weather forecasts often mention a discomfort index (or temperature-humidity index) to highlight how hot and humid the day will be. Discomfort index is calculated as:
DI = 40.6 + 0.72 (dry-bulb temperature + wet-bulb temperature ).
Here, dry bulb temperature is the “ambient temperature” (not considering humidity), while wet bulb temperature accounts for humidity by looking at how low the temperature can get by evaporating water.
Evaporation absorbs heat but can only happen if the air is not saturated with humidity. Therefore, the more humid it is, the more “discomfort” we feel as we cannot sweat off the heat building up inside our bodies.
When the DI is at 70, about 10% of people experience discomfort. At 75, 50% feel discomfort and at 80, most people will feel extremely uncomfortable. A DI of above 85 is virtually intolerable and anything above this, serious conditions such as heat exhaustion and heat stroke can occur.
As our core body temperature rises and we cannot cool down by sweating, we experience thermal stress. Under thermal stress, our concentration and task performance begins to suffer – a phenomenon people will describe as their brain feeling as if it is melting. This is a well-established phenomenon that has significantly affected how architects design offices and homes to improve air flow and temperature control to create an environment with the least thermal stress possible – for both efficiency and comfort.
On a hot summer’s day, one tends to drink cold drinks and eat cold foods to try cool their body down. But an old Korean proverb states that one should control fire with fire (yiyul-chiyul, 이열치열, 以熱治熱). In other words, instead of drinking cold drinks, it is better for your health if you eat hot soup to combat the heat. When the temperature becomes hot, the body redirects blood flow to the skin to cool itself, meaning there is less blood flow to the organs and causing the internal temperature to drop. Although cooling yourself is good, having a cold drink rapidly on a hot day can suddenly cause a large temperature difference between the surface and the organs, leading to digestive problems. In severe cases, it can cause abdominal pain and diarrhoea, with a vicious cycle where the heat is trapped on the surface and you feel even hotter. Ergo, having a hot food like samgyetang (a Korean chicken soup with many nutritious foods to revitalise your health in the summer) warms the organs and allows for better communication between the organs and the skin to effectively overcome the heat.
The philosophy of yiyul-chiyul can be extended beyond the scopes of medicine. Just as the proverb defeat savages with savages (yiyi-jeyi, 이이제이, 以夷制夷) says, one can control a certain force by using the same force on it. A great example is backfires. A forest fire tends to be too large in area to be extinguished with water. But if you deliberately start a fire just beyond its trajectory, it will burn everything as it moves towards the forest fire. Eventually the two fires will meet and without any fuel to consume, both will be extinguished.
A person’s body temperature is always maintained between 36.5~37.5°C. This is because enzymes, which are crucial in all physiological reactions in the body, work most efficiently at this temperature. As physiology is essentially a series of chemical reactions, it is heavily dependent on temperature. If the temperature falls, chemical reactions occur slower and vice versa. When body temperature falls below 35°C, metabolism becomes too slow and it poses a risk to the person’s health. This is known as hypothermia.
How does hypothermia affect the body? Hypothermia is categorised into three classes depending on the severity.
Mild hypothermia (32~35°C) leads to the slowing of bodily functions, tremors and difficulty in walking. The patient’s speech is impeded and other neurological symptoms such as decreased judgement skills and confusion start to appear. Also, blood pressure, pulse and breathing rate rise.
Moderate hypothermia (28~32°C) causes paralysis of muscles and extreme fatigue (they may complain of being sleepy). As blood (carrying heat) is rerouted to major organs, the skin (especially lips and extremities) become white or purple and very cold. Neurological symptoms worsen with amnesia, memory loss, severe confusion and delusion beginning to show. As sustained hypothermia leads to the tremors stopping, one should not take the lack of tremors as a good sign. Heart rate becomes irregular and arrhythmia may occur.
Severe hypothermia (20~28°C) leads to chemical reactions becoming so slowed that physiological functions that support life decline dramatically. Heart rate, blood pressure and breathing all lower to dangerous levels and the heart and lungs may stop functioning. As the patient’s major organs begin to shut down, they enter a state of unconsciousness and eventually, clinical death.
As you can see, hypothermia is a highly dangerous situation that can kill. There are some other fascinating facts about hypothermia.
20~50% of hypothermia death cases are associated with paradoxical undressing. This is a strange phenomenon where the person begins to take off their clothes due to confusion and a lack of judgement from the hypothermia. One theory suggests it is related to the cold damaging the hypothalamus (which controls body temperature), causing the brain to think that the body temperature is rising. Whatever the reason, it is extremely dangerous as it worsens the hypothermia.
As explained above, severe hypothermia leads to death. But interestingly, hypothermia also protects organs. This is why organs for transplanting are transported in ice. Similarly, there are examples of people who “died” from hypothermia recovering with no brain damage. Because of this, medical professionals traditionally say: “they’re not dead until they’re warm and dead”. In fact, if there is something wrong with the patient’s circulation and there is risk of damage to their organs (such as in surgery), sometimes the patient’s body temperature is forced down with ice water injections and cooling blankets, known as protective hypothermia.
A water bear, also called a tardigrade, is actually an insect and not a bear. The nickname is due to its slow, bear-like gait. It ranges in size from 0.1 to 1.5mm and resembles a short caterpillar with eight legs.
The reason for the water bear’s fame is its amazing survivability. In short, a water bear can live anywhere.
Water bears are capable of cryptobiosis. This can be seen as an extension of hibernation and it is an organism’s ability to lower its metabolism to near-death rates in order to survive a harsh environment. In this state, a water bear can survive for indefinite amounts of time.
Why is cryptobiosis useful? The answer can be found from the water bear’s natural habitats. The water bear is found on the highest point of the Himalayas, the deepest oceans, hot springs and virtually any location from the North Pole to the South Pole. It can survive temperatures from 151°C to minus 273°C, the intense pressures in deep seas and even vacuum states.
Furthermore, water bears can survive in space. A recent experiment by NASA on the International Space Station found that not only can they live in space, but they also mated and laid eggs that later hatched. They can even survive heavy doses of radiation and toxic chemicals.
Ergo, if a cockroach can survive a nuclear war, water bears can survive even if the Earth was split in two. If we took a leaf out of the water bear’s book and lead a slower life, could we live a longer and happier life?
It is a common chemical fact that water is flavourless and odourless. However, most people will know that water “tastes” subtly different each time. Taste is composed of information from taste buds on the tongue, combined with the sense of smell from your nose. Although water itself has no flavour or smell, it has many things dissolved in it such as gases and minerals that can be tasted. This is why tap water can taste bad due to the chlorine used to treat it, or metals such as copper that have come off the pipes.
It is also well known that temperature affects the taste of water. The ideal temperature is between 10~17°C, where oxygen saturation is sufficient, giving the water a “refreshing” taste. Any hotter and the oxygen escapes, giving the water a flat taste, just like distilled water. Warm water also causes the brain to think it is saliva or mucus, sometimes producing an uncomfortable sensation. Any colder, the tongue is numbed and it loses its ability to taste.
When making tea, the ideal temperature is 70~80°C. A simple way to achieve this is by leaving a cup of boiled water for a minute or two before putting the teabag in. This is the temperature when the dissolving of the various chemicals in tea leaves is optimal. If it is too hot, bitter-tasting tannins and catechins are released in excess, whereas if it is too cool, not enough dissolving occurs.
The sound of crickets in the autumn night is quite inspiring. Only male crickets can make this clear and beautiful sound, by rubbing their serrated wings against each other.
There are four kinds of cricket chirps: an attracting song (for females), a courting song (when a female is near), an aggressive song (when a male is near) and a copulatory song (after a successful mating). Each song is played at a different volume and pitch.
As all insects are cold-blooded, they are heavily affected by temperature. In the case of crickets, this is reflected in the frequency of chirps, which increases proportionately to the temperature. Using this, one can calculate the air temperature from the number of chirps a Snowy Tree cricket makes (count the number of chirps in 14 seconds plus 40 to get the temperature in Fahrenheit).
Finally, cricket chirps cannot be heard via cellphones. This is because a cricket chirp is usually around 6500Hz frequency, while most cellphones operate at a maximum of 3300Hz.