(CN) — It’s no secret that humid heat is much more difficult to handle than dry, desert-like heat, and recent studies have found that by the end of the century the tropics and subtropics could see heat and humidity reaching levels rarely, if ever, experienced by humans before.
According to scientists, the combined heat and humidity will be detrimental to economies and may even pass the physiological limits of human survival.
But in a study published Friday in the journal Science Advances, authors Colin Raymond, a postdoctoral researcher at NASA's Jet Propulsion Laboratory and Tom Matthews, a lecturer in climate science at Loughborough University in the United Kingdom, say the previous predictions are incorrect — because they’re already occurring.
The authors identify thousands of previously rare or unprecedented occurrences of extreme heat and humidity in Asia, Africa, Australia, South America and North America, including in the U.S. Gulf Coast region. For example, along the Persian Gulf researchers recorded more than a dozen events in which conditions surpassed the theoretical limit of human survivability. So far, these outbreaks have been localized and only lasted for a couple hours at a time, but the authors say they are increasing in frequency and intensity.
"Previous studies projected that this would happen several decades from now, but this shows it's happening right now," said lead author Colin Raymond, who did the research as a doctoral student at Columbia University's Lamont-Doherty Earth Observatory. "The times these events last will increase, and the areas they affect will grow in direct correlation with global warming."
To get a complete picture of the issue, the authors analyzed data from weather stations from 1979 to 2017 and found events of combined extreme heat and humidity doubled over the study period. Several of these repeated incidents took place across India, Bangladesh and Pakistan, northwestern Australia, and along the coasts of the Red Sea and Mexico's Gulf of California.
The highest and most potentially fatal readings were spotted 14 times in the cities of Dhahran/Damman, Saudi Arabia; Doha, Qatar; and Ras Al Khaimah, United Arab Emirates, with combined populations of over 3 million. Other locations also hit with these extreme conditions include parts of southeast Asia, southern China, subtropical Africa and the Caribbean.
The southeastern region of the United States experienced extreme conditions dozens of times, particularly near the Gulf Coast in east Texas, Louisiana, Mississippi, Alabama and the Florida Panhandle. These conditions also reached inland into Arkansas and along the southeastern coastal plain, with the worst cases hitting New Orleans and Biloxi, Mississippi.
As expected, such incidents tended to cluster on coastlines along confined seas, gulfs and straits, where evaporating seawater provides abundant moisture that gets sucked into the hot air. Areas more inland that experience moisture-laden monsoon winds or wide areas of crop irrigation seem to follow the same trend.
The authors note previous climate studies failed to recognize these incidents in the past because climate researchers normally look at averages of heat and humidity measured over large areas and over several hours at a time. On the other hand, Raymond and his colleagues drilled directly into hourly data from 7,877 individual weather stations, which allowed them to identify shorter-lived bouts affecting smaller areas.
Humid heat is much more dangerous than dry heat because humans cool their bodies by sweating, which carries away excess body heat through evaporation. This process is effective in desert regions, but in humid areas the air is already too heavy with moisture to take on much more and the evaporation of sweat is slowed or stopped altogether.
In the most extreme instances, unless a person can escape to air conditioning, their body’s core can heat beyond its narrow survivability range and their organs will begin to fail. Under these conditions, even the strongest, healthiest person with no clothes, abundant shade and drinking water would perish within hours.