In recent years, with climate change leading to an increase in global temperatures, extreme heat climate is gradually becoming a major health threat to humans, the human body's ability to withstand a certain degree of flexibility, but the human body can withstand the temperature is limited, so what is the maximum temperature that the human body can withstand?

　　In fact, the answer is simple! According to a study published in 2020 in the journal Science Advances, the wet bulb temperature reaches 35 degrees Celsius, which is different from the air temperature one sees reported in local weather forecasts or favorite weather apps; instead, the wet bulb temperature is measured by a thermometer covered with a cloth soaked in water, which takes into account heat and humidity differences. Humidity is important because the more moisture in the air, the harder it is to evaporate sweat and the harder it is to achieve cooling of the body.

　　NASA Jet Propulsion Laboratory postdoctoral researcher Colin Raymond, who has been working on extreme hot climate research for many years, pointed out that if both humidity and temperature are very high, the wet bulb temperature may climb to dangerous levels, for example: when the air temperature of 46.1 degrees Celsius, relative humidity of 30%, the wet bulb temperature is about 30.5 degrees Celsius; but when the air temperature of 38.9 degrees Celsius, relative humidity of 77% the wet bulb temperature is about 35 degrees Celsius.

　　The reason people can't survive in high heat and humidity is that they can no longer regulate their internal temperature, Raymond said, "If the wet bulb temperature is higher than the body temperature, the body can still sweat, but you can't get the body to cool down to the temperature needed for physiological functioning."

　　According to the National Institutes of Health, the body becomes hyperthermic at this point, with body temperatures above 40 degrees Celsius, which can lead to symptoms such as increased pulse rate, altered mental status, decreased sweating, fainting and coma.

　　However, a wet bulb temperature of 35 degrees Celsius does not immediately kill people, Raymond said, and it takes about three hours to reach a temperature that the body can not withstand. We currently have no way to determine the time limit for the body to withstand, but studies have tried to assess the exact time by immersing the body in a hot water tank and removing it when the body temperature begins to rise uncontrollably. There is no definitive way to confirm that 35 degrees Celsius is the definitive wet bulb temperature limit at which humans cannot survive, and the true critical temperature should be between 34-36.5 degrees Celsius.

      Although no one can survive at wet bulb temperatures higher than 35 degrees Celsius, cold conditions can also be fatal. Exercise and direct exposure to sunlight make it easier for the body to overheat, and some obese elderly people in poor health, as well as people taking antipsychotic drugs, cannot regulate their body temperature, so hot environments are more likely to cause them to die. This is why people sometimes die without reaching a wet bulb temperature of 35 degrees Celsius.

　　Fortunately, air conditioning can save people from unlivable heat, but not all people can enjoy the coolness that comes with air conditioning, and even though many homes are equipped with air conditioning systems, the high-load summer power grid may not be able to support the smooth operation of air conditioners.

　　According to a study published in the journal Science Advances, there are very few areas where wet bulb temperatures have reached 35 degrees Celsius since human history began, and since the late 1980s, global heat hotspots have been central Pakistan and the northern Indus Valley and the southern Persian Gulf, Raymond said, "As the global climate gradually warms, the situation will only intensify and become more widespread, and areas such as northwestern Mexico, northern India, Southeast Asia and West Africa are also expected to face the risk of high temperatures in the next 30-50 years.