Heat stress can turn deadly even sooner than experts thought. Are new warnings needed?

Gwen Osborne, a 72-year-old retired newspaper reporter from Chicago, liked to spend long hours in her apartment reading the Bible and writing. It was also where she died, overcome by the temperatures of a heat wave in the Midwest.

Osborne was one of three residents who died in the same building in May 2022. The building had a policy of not turning on the air conditioning until June.

“After three consecutive days of above average temperatures…they decided to do health screenings. And when they did her unit’s health screening, she had passed,” said her son, Ken Rye.

In the era of of Climate Change It is heating temperaturesO impact of extreme heat in people over 65, like Osborne, is a serious public health problem because they are the most vulnerable to warm disease and death.

New to look for from Penn State University found that extreme heat can begin to stress the human body at much lower levels of heat and humidity than previously thought.

“Heat stress is what kills,” said Dr. Larry Kenney, a professor of physiology and kinesiology at Penn State who specializes in how the body regulates temperature, especially for older adults.

Heat Index vs. Wet Bulb Temperatures: What’s the Difference?

Meteorologists and government agencies like the National Weather Service often use a measurement called heat index to determine how dangerous temperatures perhaps. It combines heat and humidity to give a sensation of temperature.

And while the heat index tells us what temperatures are like, Kenney is concerned that it doesn’t tell us how much damage heat and humidity do to the human body.

“When our body temperature rises and we can’t get rid of that heat, it puts a strain on the cardiovascular system,” he said.

A better measure, according to Kenney, is the humidity thermometer, which is a way of measuring thermal stress. Like heat index, wet bulb measurements consider temperature and humidity. But wet bulb temperatures also include wind speed, sun angle, and cloud cover. It is a measure frequently used by military and sporting events to assess danger.

For the past two decades, scientists have worked under the theory that prolonged exposure to a wet bulb temperature of 95 degrees — that’s 95 degrees Fahrenheit and 100% humidity — was the human body’s upper limit for compensating for heat.

But until Kenney looked deeper, this theory had never been tested in humans. He and his colleagues at Penn State found that these upper limits start much lower, at a wet-bulb temperature of about 87 degrees, which is 87 degrees F and 100% humidity.

Consequently, the the risk of heat illness is greatly increased to many more people, and sooner than anticipated, under the lowest theoretical standard.

These results were obtained in test subjects who performed “minimal” activities such as fidgeting or brushing their teeth, according to Kenney’s study. If the researchers increased the test subjects’ activity to “light ambulatory activities” such as gardening, washing dishes or gentle walks, the critical threshold decreased even further, to a wet bulb temperature around 82 degrees, or 82 degrees F and 100% humidity.

Very hot and humid places around the world, such as South Asia and the Middle East, will be the first to reach these types of conditions.

But in the United States, as summer becomes hotter and wetter due to climate change, cities in the Midwest and East Coat will begin to breach that lower danger zone, at about 5.5 degrees F. heating.

If the Earth warms further – 7 degrees F – places like Chicago and Houston could see up to 30 hours or more per year of temperatures above critical thresholds.

Creating new standards

As these threats loom, Kenney says we need to move away from the heat index’s “sensitive” temperatures.

“I think we need to look deeper into the human body in terms of how we respond to conditions of high heat and humidity, and then base new standards on that type of physiological response,” Kenney said.

One of the few places that is happening is the Australian Open tennis tournament.

Starting in 2019, the Australian Open began using a “thermal stress” scale with numbers from 1 to 5, based on wet bulb temperatures, but which is simpler to understand.

Each level of the scale has a specific recommendation, such as taking extended breaks or suspending the game.

Kenney said a similar scale could be tailored to the vulnerabilities of seniors.

“I think that would be more valuable, more valid and more reliable in alerting the public,” he said.

And Kenney hopes this can give us a better understanding of how damaging heat and humidity can actually be, rather than learning it the hard way like Ken Rye did with his mother.

“We can do better for our seniors,” Rye said.