The cooling effect of evaporation is measured scientifically as the wet bulb temperature (WBT).
It is determined by placing a sock, which has distilled water wicking into it, over a temperature sensor such as a thermometer or thermal couple.
The amount of evaporative cooling is determined by the ambient temperature and humidity — the higher the temperature the greater the rate of evaporation and cooling; the higher the humidity, the lower the rate of evaporation and cooling.
This is important to us because in hot weather we perspire, the sweat evaporates, and the cooling effect maintains our bodies at an optimum operating temperature of about 37°C.
As the air temperature increases, we sweat more and cool more — providing the humidity is low enough to allow evaporation. If a high temperature is combined with a high humidity, the evaporation stops and our bodies can no longer cool themselves. At WBTs above 35°C we die from hyperthermic overheating. A healthy body can endure this situation for about six hours; a less fit body will die at a lower WBT.
One part of the world has already reached this fatal WBT. People do not have permanent settlements in the Northern Afar Desert in Africa, west of the Red Sea, because their bodies cannot endure the heat. In July, 2015, the Iranian city of Bandar Mahshahr almost reached this WBT of 35°C when temperatures reached 46°C with a humidity of 50 per cent.
During the same unprecedented heat wave, the Gulf states exceeded 50°C and reached a WBT of 34.6°C, causing significant deaths. Other heat waves in India and Pakistan have come close to WBT.
A study by Professors Jeremy Pal and Elfatih Eltahir from the Massachusetts Institute of Technology (Nature Climate Change, Oct. 26/15) has found that if we don’t radically reduce carbon dioxide emissions, global average temperatures could rise 4°C above pre-industrial levels by 2100, dramatically increasing the occurrence of WBTs. For Saudi Arabia, Abu Dhabi, Dubai, Doha and the coastal regions of Iran, present extremes would become normal summer temperatures, and WBTs would be common by 2070.
“Our results,” the professors write, “expose a specific regional hotspot where climate change, in the absence of significant [carbon cuts], is likely to severely impact human habitability in the future.”
For the Gulf states particularly, oil production is suicidal. The wet bulb temperature and the brief 34 years we have until 2050 should be stark reminders, however inconvenient to plans and budgets, that we must immediately end all development and infrastructure related to fossil fuels.
Lives depend on it.