Heat index values exceeded 160 degrees on 31July2015 near the Persian Gulf. This combination of heat and humidity is close to the limits of human survival. Unchecked global warming will cause the steamy conditions to exceed the limits of survival.
In the summer months, hot air from the Asian monsoons sinking over the Persian Gulf causes a layer of steamy air to form above the hot gulf water. The sinking monsoon air is so hot that the slightly cooler air below does not mix into it. Instead of mixing, enormous amounts of water evaporate off of the hot Gulf water trapping the earth's steamiest air in the marine air layer above the Gulf. This marine layer takes up enormous amounts of solar heat to the point that it is almost deadly to any form of warm blooded life that isn't inside a dwelling or living under a rock. This summer the heat index or "feels like temperatures", which are a measure of the combined effects of heat and humidity, reached 160°F in several cities on the Persian Gulf. A sea breeze off the Gulf, instead of bringing cool marine air inland, as it does in the United States, brought in a layer of insufferable steam to Iranian towns. Residents fled to air conditioning or cooled off under hoses of water. It was literally too hot to do any work outside.
A study just published shows that if greenhouse gas emissions continue to rise the absolute humidity, measured as the dew point or wet bulb temperature will rise to 95°F (35 Celsius) or higher, which is above the threshold of human survival. Sea breezes that blow off of the Gulf may bring in air that is so hot and humid that the human body will not be able to cool itself. In simple terms, humans would be steamed to death if they remained outside for 6 hours.
The dark color in the 3 upper graphs indicates deadly levels of steaminess where dew points are 35 Celsius (95°F) or higher. The dark color in the lower set of graphs indicates temperatures of 60 Celsius (140°F) or higher. The 2 figures on the left are present values. The center and right figures are the modeled maximum values in the 30 year period from 2070 to 2100. The blue zones would be effectively uninhabitable like the Afar region in north Africa.
The extreme heat and humidity will threaten the lives of Muslim pilgrims to Mecca.
The scientists used standard climate computer models to show that the fatal WBT extremes would occur every decade or two after 2070 along most of the Gulf coast, if global warming is not curbed. Using the normal measure of temperature, the study shows 45C would become the usual summer maximum in Gulf cities, with 60C being seen in places like Kuwait City in some years.
Near the Red Sea coast of Saudi Arabia, where Mecca and Jeddah lie, the Wet Bulb Temperature (WBT) is not projected to pass the fatal 35C level, but would be 32C or 33C. This would make the Hajj extremely hazardous, said the scientists. “One of the rituals of Hajj – the day of Arafah – involves worshipping at the site outside Mecca from sunrise to sunset. In these kind of conditions, it would be very hard to have outside rituals,” said Eltahir.