The human body functions normally when it maintains the temperature of 36.8 degrees. If the body temperature continues to be higher than that by 3 degrees, life becomes dangerous. To this end, the body has a central body that regulates metabolic activity in the body to maintain the proper temperature. It is the hypothalamus that governs the autonomic nervous system. The hypothalamus expands blood vessels and increases heart rate when body temperature rises. The goal is to lower body temperature by transferring heat from the body to the skin more quickly. At the same time, it releases heat by allowing you to sweat more.
The most important part of the body's body temperature control action is evaporation, that is, sweating. 75% of body heat loss is achieved through evaporation of sweat. However, when the external humidity is high, sweat cannot be easily evaporated. So, wet heat is more frightening than dry heat. This is why the humid heat of Korea during the summer rainy season is more annoying and difficult to endure than the hot dry heat of the desert.
By looking at the wet-bulb temperature (TW) that reflects both the temperature and the humidity, it is possible to grasp the limits of temperature and humidity that a human can withstand. The wet bulb temperature is the temperature measured by wrapping the tip of mercury with a cotton swab dipped in water. The limit that humans can withstand physiologically is known as the wet bulb temperature of 35 degrees Celsius. When the wet bulb temperature reaches this point, the body temperature cannot be cooled by sweat. The skin temperature is maintained at 35 degrees, slightly lower than the temperature in the body, and the heat generated by metabolism in the body is discharged through sweat, and when the wet bulb temperature reaches this point, the body cooling system does not work. The theory is that it cannot last more than 6 hours. Since the assumption is based on the premise that a healthy person rests comfortably without drinking clothes under the shade, the actual limit is lower than this. A wet bulb temperature of 35 degrees corresponds to 45 degrees Celsius in a 50% humidity environment.
What is the condition of the wet bulb temperature of the earth now that is undergoing climate change due to greenhouse gases? Climate models published so far have predicted that if the greenhouse gas is emitted in the same trend as now (RCP8.5), the wet bulb temperature of 35 degrees will appear after the middle of the 21st century. However, studies have warned that the limit is approaching faster than expected.
US researchers, such as Colleen Raymond, a researcher at the California Institute of Technology (Caltech), analyzed about 40 years of data from 4,000 weather stations around the world (1979-2017) and found that wet bulb temperature in some regions has already exceeded the survival limit of 35 degrees. The Earth has passed the junction of passing through the 'cool Earth' and entering the 'Steambath Earth'. The researchers found that the wet bulb temperature of more than 35 degrees persisted for 1-2 hours in the Indus River basin in India and Pakistan, the Red Sea coastal region of the Persian Gulf in the Middle East, and the southwestern coastal region of North America.
The Gulf of Mexico, the Gulf of California, the Caribbean, West Africa, and South China were also in danger. In 2017, there were about 1,000 times the wet bulb temperature in the world exceeded 30 degrees. This is more than twice as many as in 1979. Considering that the wet bulb temperature was 28 degrees during the heat wave in Europe, which caused 70,000 people to die in 2003, the frequency of life-threatening heat waves has increased more often.
According to the interactive map released by the researchers, the highest wet bulb temperature in Korea was 30.3 degrees in Incheon, 28.9 degrees in Daegu, 29.5 degrees in Suwon, 30 degrees in Gunsan, 30.5 degrees in Seosan, and 27.5 degrees in Yeongdong, Chungbuk. Raymond said, "For a wet bulb temperature of 33 degrees, which is slightly below the limit, it occurred only once or twice a year 40 years ago across the globe, but now it occurs 25 to 30 times."
"If the global average temperature is 2.5 degrees higher than before industrialization, some parts of the world will periodically exceed the wet bulb temperature of 35 degrees," the researchers predicted. The global temperature is now 1 degree higher than before industrialization.
The study was published in the science journal Science Advance on May 8th.