2.2 bn could face heat waves beyond survival limit: Study

India and the Indus Valley, with a combined population of around 2.2 billion, will experience the first deadly moist heat waves and, subsequently, substantial increases in accumulated hot hours per year, a new paper published in Proceedings of the National Academy of Sciences has said.

- Jayashree Nandi

The paper led by Penn State College of Health and Human Development and the Purdue College of Sciences and Purdue's Institute for a Sustainable Future also flagged that Indian cities such as Delhi and Kolkata; Pakistan's Lahore; Bangladesh's Dhaka; China's Shanghai and Beijing are expected to start recording considerable "hot hours" annually even at 1.5 and 2 degree C warming over pre-industrial levels. For example, Delhi is projected to record 16 annual hot hours at 1.5°C warming which increases to 39 hot hours at 2°C and 170.7 hot hours at 3°C warming.

A wet-bulb temperature of 35°C has been proposed as a theoretical upper limit on human abilities to biologically thermoregulate. But, recent research using human subjects found this threshold to be significantly lower--in other words, even with minimal activity, the human body will not be able to cool down at a much lower temperature than thought before.

In 2022, authors and their collaborators demonstrated that the limits of heat and humidity people can withstand are lower than were previously theorised.