Heat stress… A climate threat to human existence?
The global average temperatures have increased by approximately 1.1 to 1.2 degrees Celsius compared to the pre-industrial era. This has affected all forms of life on Earth, including humans, as not all of them can tolerate the high temperatures and have succumbed to what is known as “heat-related mortality.” In 2015, 196 countries signed the Paris Agreement, aiming to limit the global temperature increase to 1.5 degrees Celsius above pre-industrial levels.
However, a recent study has found that with global temperatures rising by 1.5 degrees Celsius above pre-industrial levels, it will cause severe harm to human health worldwide due to the human body’s inability to cool itself. The study was published in the “Proceedings of the National Academy of Sciences” on October 9, 2023.
How does the human body regulate its internal temperature? When the ambient temperature rises, the human body takes certain measures to maintain its internal temperature, including:
- Sweating: Typically, the human body sweats in high-temperature environments, which helps cool the skin and, in turn, regulates internal temperature.
- Vasodilation: With rising temperatures, blood vessels under the skin expand, leading to increased blood flow to the skin, making it cooler, allowing the body to release heat.
Heat Tolerance Limits
Human bodies can tolerate a certain range of temperatures, known as “heat tolerance limits.” Beyond these limits, the body is at risk of health issues related to heat, such as heatstroke or heart attacks. Sometimes, temperature levels can drop below the heat tolerance limits defined by scientists, as seen in the extreme heatwave in Oregon, United States, in 2021, where over 700 people lost their lives.
Typically, the heat tolerance limits are lower for the elderly than for the youth. Looking back in history, the 1995 Chicago heatwave in the United States claimed the lives of over 730 people, mostly over the age of 65.
Worst-Case Scenarios
Scientists have developed models in which global temperatures may rise between 1.5 to 4 degrees Celsius to identify areas where heat levels and humidity exceed human heat tolerance limits.
Two Degrees
If global temperatures rise by two degrees Celsius above pre-industrial levels, it could adversely affect nearly 3 billion people living in regions like Pakistan, the Sindh Valley, East China, and the greater African Sahel region. These areas are likely to experience heatwaves and high humidity levels, affecting the skin’s ability to sweat, which is the body’s means of cooling. Importantly, many of the affected regions are economically classified as low to medium income, which means a significant portion of those impacted may not have access to the means to adapt to such conditions.
Three Degrees
In the case of an average global temperature increase of over 3 degrees Celsius above pre-industrial levels, it means that heat and humidity will exceed human tolerance limits, especially along the eastern coast and central United States, South America, and Australia.
Four Degrees
Perhaps this is the worst-case scenario where the affected region becomes uninhabitable. For instance, the city of Al Hudaydah in Yemen, a coastal city on the Red Sea with a population of 700,000. With global temperatures rising by 4 degrees Celsius above pre-industrial levels, it is expected that this city will experience more than 300 days a year with temperatures exceeding human heat tolerance limits, making it unsuitable for habitation.
Therefore, the study’s authors recommend the urgent need to reduce greenhouse gas emissions and maintain global average temperatures below levels that could lead to the loss of human lives and increased suffering.
