Climate driven extreme heat threatens human habitation on earth

If global temperatures rise by 1 degree Celsius or more beyond their current levels, billions of individuals annually will face conditions of extreme heat and humidity that hinder their natural ability to cool down

Research conducted by the Penn State College of Health and Human Development, in collaboration with Purdue University College of Sciences and the Purdue Institute for a Sustainable Future, reveals.

Reducing greenhouse gas emissions

The human body can endure specific combinations of heat and humidity. Still, once these thresholds are exceeded, individuals are susceptible to heat-related health issues, such as heatstroke or heart attacks. As global temperatures continue to rise due to climate change, there is a growing concern that billions of people may exceed these limits.

“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, professor of physiology and kinesiology, the Marie Underhill Noll Chair in Human Performance at Penn State and co-author of the new study.

According to research conducted by Penn State last year, young and healthy individuals have an ambient wet-bulb temperature threshold of around 31 degrees Celsius, equivalent to 87.8 degrees Fahrenheit at 100% humidity. This threshold is not fixed and varies based on an individual’s physical activity and various environmental factors, such as wind speed and solar radiation.

Throughout human history, instances of temperature and humidity surpassing the limits of human tolerance have been rare and typically occurred for only a few hours at a time, primarily in regions like the Middle East and Southeast Asia, as reported by the researchers.

Impact on lower-income nations

The study shows that if global temperatures rise by 2 degrees Celsius above preindustrial levels:

1. The Indus River Valley in Pakistan and India, Eastern China, and sub-Saharan Africa will regularly experience high heat and humidity, making it hard for people to cope.
2. These areas will face humid heatwaves, which are particularly risky because the air can’t absorb extra moisture, making it challenging for people to cool down. Unfortunately, many people in these regions may not have access to air conditioning or other ways to protect themselves from the heat.

If the planet continues to warm to 3 degrees Celsius above preindustrial levels:

1. The Eastern Seaboard and the central United States (from Florida to New York and Houston to Chicago) will start experiencing extreme heat and humidity issues.
2. South America and Australia will also face extreme heat.

The United States will have more heatwaves, but they won’t frequently exceed human limits. However, these models might not account for the most extreme weather events.

In recent years, Kenney and his research partners have undertaken 462 distinct experiments to record the thresholds of heat, humidity, and physical activity that humans can endure before their bodies cannot maintain a stable core temperature.

Huber, who had already initiated efforts to map the consequences of climate change, reached out to Vecellio to discuss a potential collaboration.

In partnership with Huber and his graduate student Qinqin Kong, the researchers decided to investigate the potential impacts on people in various global regions if the planet’s temperature were to increase by anywhere from 1.5 degrees Celsius to 4 degrees Celsius. The researchers noted that, in the absence of significant interventions, 3 degrees Celsius is the most likely estimate for how much the planet will warm by the year 2100.

The threat of extreme heat

Extreme heat and humidity should always be a concern, regardless of the extent of global warming, as they can have adverse effects even when they fall within human tolerance limits. In studies involving older populations, Kenney found that older adults are more prone to heat stress and related health issues at lower heat and humidity levels than younger individuals.

While this study mainly focused on the body’s core temperature, the researchers pointed out that people can face health problems during heat waves for various reasons. For example, during the 1995 heatwave in Chicago, most of the 739 individuals who passed away were over 65 and experienced a combination of elevated body temperature and cardiovascular problems, contributing to heart attacks and other cardiovascular-related causes of death. 

To prevent further temperature increases, the researchers emphasise the importance of reducing greenhouse gas emissions, particularly carbon dioxide, from burning fossil fuels.