Unbearable heat could make some parts of the world uninhabitable if warming continues

Researchers from institutions including the Pennsylvania State University and Purdue University have recently found that if the Earth’s temperatures rise only one degree Celsius over current measurements, each year countless individuals will experience unbearable heat and humidity levels that will render their bodies incapable of cooling themselves. 

Moreover, the experts found that temperature increases of more than 1.5 C above pre-industrial times will result in significant negative impacts on human health worldwide.

Heat thresholds 

Humans have certain thresholds for the combined effects of heat and humidity. Crossing these thresholds can lead to severe health issues, like heat strokes or cardiac incidents. As the climate continues to change, these boundaries could be exceeded, putting billions at risk.

Since the industrial era’s onset, global temperatures have risen approximately 1 C (1.8 degrees Fahrenheit). This led to the 2015 Paris Agreement, where 196 countries committed to restricting global temperature rise to 1.5 C over the pre-industrial average.

Complex problems 

The scientists analyzed several potential scenarios, looking at global temperature rises from 1.5 C up to 4 C. They aimed to identify regions where human tolerance levels for heat and humidity would be breached.

“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,” said co-author W. Larry Kenney, a professor of Physiology and Kinesiology at Penn State.  

“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.”

Exceeding human limits 

A study by Penn State researchers last year pinpointed the wet-bulb temperature limit for young, healthy individuals at about 31 C (87.8 F at 100 percent humidity). Multiple factors influence this limit, such as exertion, wind speed, and solar radiation. 

The researchers noted that only a handful of instances in human history have registered temperatures and humidity exceeding human limits, typically in areas like the Middle East and Southeast Asia.

Intolerable heat levels 

The current study projects that with a 2 C temperature rise, billions residing in areas like Pakistan and India’s Indus River Valley, eastern China, and sub-Saharan Africa will regularly face intolerable heat levels. 

The scientists express concern over the high-humidity nature of these heatwaves and the socioeconomic status of these regions. Moreover, the affected populations might lack access to essential cooling measures, exacerbating health risks.

Uncertainties remain

A temperature increase of 3 C above pre-industrial levels could make places like the US’ Eastern Seaboard and central areas, South America, and Australia too hot for humans. While the US might be spared the worst direct impacts, Daniel Vecellio, the study’s lead author, cautioned that models like these might not account for extreme, unprecedented weather events.

Another 2022 study by the team found that the previously theorized limits for heat and humidity tolerance were too high. 

“The data collected by Kenney’s team at Penn State provided much needed empirical evidence about the human body’s ability to tolerate heat. Those studies were the foundation of these new predictions about where climate change will create conditions that humans cannot tolerate for long,” said co-author Matthew Huber, a professor of Earth, Atmospheric and Planetary Sciences at Purdue.

Study implications 

Huber’s graduate student, Qinqin Kong, emphasized the need for governments to address the threat of humid heat, which poses more danger than dry heat. 

“Around the world, official strategies for adapting to the weather focus on temperature only. But this research shows that humid heat is going to be a much bigger threat than dry heat. Governments and policymakers need to re-evaluate the effectiveness of heat-mitigation strategies to invest in programs that will address the greatest dangers people will face,” he said.

The experts advised the public to always be vigilant regarding extreme heat events, particularly for vulnerable groups like older people. 

“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 40C last summer,” said lead author Daniel Vecellio, a bioclimatologist who completed a postdoctoral fellowship at Penn State with Kenney. 

Uninhabitable regions

“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.”

In order to address rising temperatures, the scientists stressed the urgent need for curbing greenhouse gas emissions, particularly carbon dioxide from burning fossil fuels. If such proactive measures are not taken, countries with middle and lower economic statuses will be hit hardest.

Highlighting the gravity of the situation, the team drew attention to Al Hudaydah in Yemen, a bustling port city on the Red Sea with a population exceeding 700,000. 

Billions will suffer

According to the study’s findings, should global warming reach an increase of 4 C, residents of this city might endure temperatures exceeding human comfort thresholds for over 300 days annually, rendering it close to unlivable.

“The worst heat stress will occur in regions that are not wealthy and that are expected to experience rapid population growth in the coming decades. This is true despite the fact that these nations generate far fewer greenhouse gas emissions than wealthy nations. As a result, billions of poor people will suffer, and many could die. But wealthy nations will suffer from this heat as well, and in this interconnected world, everyone can expect to be negatively affected in some way,” Huber concluded.

The study is published in the journal Proceedings of the National Academy of Sciences.

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