#wetbulb

Hotter than the human body can handle: Pakistan city broils in world’s highest temperatures
https://www.telegraph.co.uk/global-health/climate-and-people/hotter-human-body-can-handle-pakistan-city-broils-worlds-highest/

This city of some 200,000 in Pakistan's Sindh province has long been renowned for its fierce heat, but recent research has conferred an unwelcome scientific distinction.

Its mixture of heat and humidity has made it one of only two places on earth to have now officially passed, albeit briefly, a threshold hotter than the human body can withstand.

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Mr Matthews and colleagues last year analysed global weather station data and found that Jacobabad and Ras al Khaimah, north east of Dubai in the United Arab Emirates, have both temporarily crossed the deadly threshold. The milestone had been surpassed decades ahead of predictions from climate change models.

The researchers examined what are called wet bulb temperatures. These are taken from a thermometer covered in a water-soaked cloth so they take into account both heat and humidity.

Wet bulb thermometer readings are significantly lower than the more familiar dry bulb readings, which do not take humidity into account. Researchers say that at a wet bulb reading of 35C, the body can no longer cool itself by sweating and such a temperature can be fatal in a few hours, even to the fittest people.

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Jacobabad crossed the 35C wet bulb threshold in July 1987, then again in June 2005, June 2010 and July 2012. Each time the boundary may have been breached for only a few hours, but a three-day average maximum temperature has been recorded hovering around 34C in June 2010, June 2001 and July 2012. The dry bulb temperature is often over 50C in the summer.

Patchy death records mean it is not clear whether the crossing of the threshold resulted in a wave of fatalities. The effects of entering the danger zone are likely to be blurred, for example with cooler interiors of buildings temporarily sheltering residents from the worst. It also depends on how long the threshold is crossed.

Mr Matthews said: “Even though it's theoretically been crossed according to the weather station measurements in that part of the world, whether or not it's been crossed in the hyper local environment where people are living, and for long enough to really translate into widespread deadly conditions, is another question.”