Lethal levels of heat and humidity are gripping global ‘hot spots’ sooner than expected

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Lethal levels of heat and humidity are gripping global ‘hot spots’ sooner than expected

 

 

 

At wet bulb temperatures above 35°C, researchers estimate that even fit people will overheat and potentially die within 6 hours. Although that temperature might seem low, it equates to almost

 

45°C at 50% humidity, and what it would feel like 71°C using the U.S. National Weather Service heat index. In the heat wave that ravaged Europe, wet bulb temperatures hit 28°C.

 

Climate change will likely make these conditions more common in places such as southwest Asia, India, and China, researchers say. But their models estimate temperatures for relatively large

 

swaths of land. Likewise, analyses of past weather data assess conditions over grids of more than 700 square kilometers, potentially missing localized spikes.

 

 

Raymond wondered whether that might obscure specific hot spots where geography and weather are already conspiring to create intolerable conditions. To find out, he and his colleagues

 

combed through 39 years of hourly data from weather stations on six continents, dating back to 1979.

 

They discovered a handful of individual spots—including shorelines along the Persian Gulf and river valleys in India and Pakistan—had crossed the 35°C wet bulb threshold, though only for an

 

hour or two at a time. And in 2017, wet bulb conditions topped 30°C 1000 times—more than double the number in 1979, they write today in Science Advances.

 

Weather stations in several other places stood out. They include Mexican towns near the Gulf of Mexico and the Gulf of California, and the coastal city of San Francisco in Venezuela. Areas in the

 

Caribbean, West Africa, and southern China also had extreme readings. Weather stations in these places recorded approximately 1000 incidents registering at 31°C, while the wet bulb

 

temperature broke 33°C about 80 times, according to the researchers.

 

Many of these hot spots, which can be seen in this interactive map, have already been flagged by models.

 

To guard against errors from malfunctioning weather stations, Raymond’s group compared the data with sea surface temperatures measured by satellites and air temperatures measured by

 

weather balloons near the Persian Gulf, where the temperatures were highest.

 

Though previous work has analyzed temperature records, this new study adds insight by pairing temperature with humidity, says Noah Diffenbaugh, a Stanford University climate scientist who

 

studies temperature extremes and was not involved in the research. The result is a detailed picture that’s “highly relevant for heat stress in humans,” he says.

 

And this kind of historical data adds more evidence of growing heat extremes predicted by models, says Elfatih Eltahir, a hydrologist and climate scientist at the Massachusetts Institute of

 

Technology who forecasts extreme weather in Asia. It suggests the models might even be underestimating how soon these extremes will take hold. “In reality, maybe they are happening faster

 

[than we think],” he says.

 

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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.

 

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."

 

Source

[Karlston]

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