Intensifying climate-driven heat may surpass human tolerance

Furthermore, the study explored the effects of heat that exceeded human tolerance and could cause heat-related health problems such as heat stroke or heart attack for billions of people.

Devastating for human health

The research was conducted by a team of scientists at the Penn State College of Health and Human Development, Purdue University College of Sciences, and Purdue Institute for a Sustainable Future. 

A statement by the scientists said, “the warming of the planet beyond 1.5 C above preindustrial levels will be increasingly devastating for human health across the planet.”

The Industrial Revolution pivoted humans towards utilizing machinery and building factories that burn fossil fuels. This caused temperatures worldwide to rise by nearly 1 degrees Celsius (1.8 degrees Fahrenheit). 

As a result of global temperatures increasing, 196 countries in 2015 signed the Paris Agreement, which aimed to prevent crossing the preindustrial level 1.5 degrees Celsius threshold.

Therefore, the team of researchers conducted simulations considering worst-case scenarios of rising temperatures ranging from 1.5 degrees Celsius to 4 degrees Celsius. 

These simulations aimed to determine areas on the planet where rising temperatures would result in heat and humidity levels surpassing what humans can tolerate. 

By studying these scenarios, researchers aimed to identify regions most at risk due to climate change-induced extreme heat and humidity.

W Larry Kenney, co-author and professor of physiology and kinesiology, the Marie Underhill Noll Chair in Human Performance at Penn State, stated: 

“To understand how complex, real-world problems like climate change will affect human health, you need expertise both about the planet and the human body.”

“I am not a climate scientist, and my collaborators are not physiologists. Collaboration is the only way to understand the complex ways that the environment will affect people’s lives and begin to develop solutions to the problems that we all must face together,” added Kenney.

Penn State researchers published a study last year that determined that the ambient wet-bulb temperature limit for young, healthy people is about 31 C, equal to 87.8 F at 100 percent humidity.

There are exceptions to this phenomenon when considering temperature and humidity. An individual’s specific tolerance level at specific thresholds is also influenced by factors such as physical activity and environmental elements like wind speed and solar radiation.

Endangering billions of people

Researchers said that temperatures and humidity surpassing human limits have been recorded only a limited number of times and only for a few hours at a time in human history. These were observed in the Middle East and Southeast Asia.

The study findings revealed that a rise of 2 degrees Celsius above preindustrial levels would subject the 2.2 billion inhabitants of Pakistan and India’s Indus River Valley, the one billion individuals in eastern China, and the 800 million residents of sub-Saharan Africa to prolonged periods of heat exceeding human tolerance each year.

These regions will face high-humidity heat waves, which can be more detrimental as air cannot absorb excess moisture effectively. The limitation would affect the human body’s ability to cool down through sweat evaporation and simulate water in infrastructure like evaporative coolers.

This situation is more alarming because these regions are typically found in lower-to-middle-income nations. Consequently, a significant portion of the affected population may lack access to air conditioning or other effective means to alleviate the adverse health effects of extreme heat. 

Losing heat to the environment

Kenney explained that As people get warmer, they sweat, and more blood is pumped to their skin so that they can maintain their core temperatures by losing heat to the environment.

“At certain levels of heat and humidity, these adjustments are no longer sufficient, and body core temperature begins to rise. This is not an immediate threat, but it does require some form of relief. If people do not find a way to cool down within hours, it can lead to heat exhaustion, heat stroke, and strain on the cardiovascular system that can lead to heart attacks in vulnerable people.” 

However, if the planet continues to face accelerating heat goes beyond 3 degrees Celsius above preindustrial levels, the researchers inferred, “heat and humidity levels that surpass human tolerance would begin to affect the Eastern Seaboard and the middle of the United States — from Florida to New York and from Houston to Chicago. South America and Australia would also experience extreme heat at that level of warming.”

The researchers predicted that the United States would encounter more heatwaves, but the heatwaves may not exceed human limits often compared to other parts of the world. 

However, scientists are cautioned that these models frequently overlook extreme and unusual weather events.

Daniel Vecellio, lead author and a bioclimatologist who completed a postdoctoral fellowship at Penn State with Kenney, stated: 

“Models like these are good at predicting trends, but they do not predict specific events like the 2021 heatwave in Oregon that killed more than 700 people or London reaching 40 C last summer.”

“And remember, heat levels then were all below the limits of human tolerance that we identified. So, even though the United States will escape some of the worst direct effects of this warming, we will see deadly and unbearable heat more often. And — if temperatures continue to rise — we will live in a world where crops are failing and millions or billions of people are trying to migrate because their native regions are uninhabitable,” Vecellio warned.