A dangerous combination of heat and humidity is sweeping the Gulf region this week, hitting cities from Dubai to Doha.
Dubai, for example, is forecast to see air temperatures hover around 43C. But climate experts say air temperature alone can be misleading.
Meteorologists are particularly worried about the ‘wet-bulb’ temperature – a more holistic measurement that accounts not just for air temperature but also how much moisture it holds. In Dubai, humidity this week is expected to be between 35 per cent and 45pc.
At the upper end, wet-bulb temperatures can cause serious health effects if people can’t find a way to cool down quickly.
Dubai could this week briefly touch wet-bulb temperatures nearing 30C – roughly the point at which serious health effects could occur – but would need to sustain that temperature for several hours, which isn’t yet expected.
A wet-bulb measurement is taken by covering a thermometer with a water-soaked cloth. The process of the water evaporating from the cloth, thus lowering the temperature, mirrors how the human body cools down with sweat.
At 100pc relative humidity, the wet-bulb temperature will be the same as the dry air temperature, but with less humidity, it is lower.
High wet-bulb temperatures are dangerous because humans lose around 80pc of heat through sweating, so when both humidity and air temperature are high it becomes harder to shed excess heat.
Sweat evaporates very slowly, if at all, in very humid conditions.
If the body cannot cool down it will eventually overheat, triggering respiratory and cardiovascular issues, and even death.
This is an area of ongoing research among scientists.
A landmark study in 2010 found that a wet-bulb temperature of 35C persisting beyond six hours could induce hyperthermia in people and cause serious health consequences or death.
Climate change is predicted to affect not just how high wet-bulb temperatures get but also how long they persist.
The upper range of wet-bulb temperatures scales directly with the climbing global average temperature.
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