The recent IPCC report AR6 has emphasised that humidity is also very important while estimating the physiological stress that extreme heat puts on the human body


Why is humidity such a critical factor while measuring heat exposure?

  • Humans lose heat generated within their body by producing sweat that evaporates on the skin.
  • The cooling effect of this evaporation is essential in maintaining a stable body temperature.
  • As humidity rises, sweat does not evaporate —just like clothes take a long time to dry in humid locations – and makes it difficult to regulate body temperature. This is why we feel more discomfort in humid places.
  • The humidity required to reach wet bulb temperatures in excess of 35°C over land is exceedingly difficult to achieve for a variety of reasons.


Wet bulb temperature

  • In the recent IPCC report AR6, instead of the “dry bulb” temperature that is usually measured using a regular thermometer, an alternative metric known as the “wet bulb temperature” has been used to measure exposure to extreme heat.
  • The report mentions that sustained exposures to wet bulb temperatures above 35°C are fatal, while sustained exposures to wet bulb temperatures above 32°C are dangerous for intense physical activity.