Deadly 'wet bulb' heatwave threatens to make areas unsurvivable

A deadly ‘wet bulb’ heatwave is threatening the lives of millions in India and Pakistan, with hot, humid conditions that could make it impossible to survive.

For months, areas of both countries have baked in temperatures over 40ºC - but experts fear that soaring ‘wet bulb temperatures’ in some areas could turn lethal, NBC reported.

‘Wet bulb’ temperatures refer to a sort of thermometer measurement built to measure heat AND humidity.

Human beings can survive very high temperatures (well over 50ºC) when humidity is low but, in high humidity, humans cannot survive temperatures of even 35ºC for long periods, because there is no way to cool down by sweating.

Even the fittest people often die within hours in such conditions.

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Tapio Schneider, a professor of environmental science and engineering at the California Institute of Technology, says that sweating is “a very effective means of cooling, but it's crucial that the sweat can actually evaporate”.

“It’s really a hard limit for survivability. You can die just by sitting there. You don’t need to move or do anything else. There’s simply no way to cool and you overheat.”

In the near future, wet-bulb temperature could be crucial for determining which areas of our warming planet remain habitable.

Wet-bulb temperature refers to temperatures taken with a thermometer covered in a wet cloth, which are normally slightly cooler than ‘dry-bulb’ temperatures..

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Wet-bulb thermometers allow researchers to work out whether humans can sweat: if the water evaporates, the thermometer cools down, so that ‘wet bulb’ temperatures are lower than ‘dry bulb’ temperatures.

In high humidity, the water will not evaporate, and the wet-bulb temperature will be the same as the dry-bulb temperature.

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Previously, wet-bulb temperatures of 35ºC or higher were thought impossible, but last year scientists reported that places in the Persian Gulf had reached the threshold.

This happened only briefly, and only in small areas, but it could be a warning of things to come.

“It approximates how warm it feels to humans because we cool via sweating,” Tom Matthews, a lecturer in climate science at Loughborough University told the Telegraph.

“We rely on that exclusively. When you use that measure, the wet bulb temperature, the two regions that stand out on earth are the shores of the Gulf and the Indus Valley in Pakistan. They are truly exceptional.”

“The Indus Valley is arguably close to being the number one spot worldwide.”

Colin Raymond, lead author of a 2020 study into humidity, said, “Physiologically, there's a point when heat and humidity will become not just uncomfortable, but actually impossible to acclimate to.

Raymond warned that this is “already happening and only getting worse.”

Climate change will exacerbate the effect, Raymond warned.

“Previous studies projected that this would happen several decades from now, but this shows it's happening right now.

“The times these events last will increase, and the areas they affect will grow in direct correlation with global warming.”

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