Hot and Humid Weather Beyond What Human Body Can Tolerate Is Already Here

Episodes of extremely hot and humid weather beyond what the human body is theoretically capable of surviving are occurring around the world.

Climate models have predicted that these conditions would occur in parts of the tropics and subtropics by the mid-21st century. However, a comprehensive evaluation of weather station data has revealed that these dangerous episodes are already appearing in confined areas, according to a study published in the journal Science Advances.

Scientists measure the combination of heat and humidity with something called the "wet bulb" Centigrade scale, which is often translated into "heat index" or "real-feel" Fahrenheit readings in the United States.

While the human body has a remarkable ability to shed excess heat, previous research suggests that even a strong, physically fit person resting in the shade with no clothes and unlimited access to drinking water would likely die within hours in wet bulb readings of more than 35° Celsius—equivalent to a heat index of 160 Fahrenheit. This is because sweat cannot evaporate quickly enough in the saturated air, resulting in the body overheating.

However, even at wet bulb temperature of 32° Celsius, these same physically fit people would likely be incapable of carrying out normal outdoor activities. And anything in the high 20s and low 30s can be dangerous to human health.

"It's hard to exaggerate the effects of anything that gets into the 30s," Colin Raymond, lead author of the study who at the time of the research was a PhD. student at Columbia University's Lamont-Doherty Earth Observatory, said in a statement.

"High wet bulb temperatures cause people to overheat, suffering heat stroke or in extreme cases, death. When wet bulb temperatures are high, people will be unable to do strenuous activities outdoors for prolonged periods of time, such as construction, farming, and sports," Radley Horton, another author of the study from Lamont-Doherty, told Newsweek.

In the study, Raymond and colleagues analyzed data from nearly 8,000 weather stations collected between 1979 and 2017, finding that some coastal subtropical locations have already reported a wet bulb temperature of 35° Celsius.

"Previous studies projected that this would happen several decades from now, but this shows it's happening right now," Raymond said. "The times these events last will increase, and the areas they affect will grow in direct correlation with global warming."

Furthermore, the researchers found that occurrences of dangerous wet bulb temperatures of over 27°C have more than doubled since 1979.

The incidences of extreme temperature and humidity detailed in the study were highly localized in space and time, usually lasting just one or two hours.

This could explain why they were missed by previous climate research, which tends to look at averages of heat and humidity measured over large areas and for several hours at a time. In the latest study, the researchers looked at hourly data to get around this problem.

heatwave, new york city
As a heat wave descends upon New York, people seek refuge from the record high temperatures at the beach in Coney Island on July 20, 2019 in New York City. Andrew Lichtenstein/Corbis via Getty Images

The paper identifies thousands of previously rare or unprecedented episodes of extreme heat and humidity in Asia, Africa, Australia, South America and North America. In the U.S., extreme wet bulb temperatures occurred dozens of times, mainly near the Gulf Coast.

However, the highest , potentially fatal, readings were documented 14 times along the Persian Gulf in the cities of Dhahran and Damman in Saudi Arabia; Doha in Qatar and Ras Al Khaimah in the United Arab Emirates.

Most of the incidences tend to be located along coastlines, confined seas, gulfs and straits, where water is evaporated by hot air.

"We may be closer to a real tipping point on this than we think," Horton said in the statement.

"The economic and health risks of extreme humid heat have been underestimated, to the extent they have been estimated at all, in many vulnerable regions such as South Asia," he told Newsweek.

Steven Sherwood, a researcher at the University of New South Wales in Australia, who was not involved in the study, said in a statement: "These measurements imply that some areas of Earth are much closer than expected to attaining sustained intolerable heat. It was previously believed we had a much larger margin of safety."