The condition we collectively refer to as “life” only exists in a narrow set of parameters. If the environment is too hot, the building blocks of life start to unravel and fall apart. If it’s too cold, physiologic liquids become solids—not good, considering the human body is approximately 60% water.
In physiology, these conditions are referred to as hyperthermia and hypothermia, respectively. Both conditions can lead to issues with cognition, movement problems and ultimately death unless they are corrected by compensatory mechanisms such as shuttling blood to different parts of the body.
It appears hyperthermia (an increase in core body temperature) may currently pose a bigger threat to humans and animals. In the U.S., heat-related deaths are the leading cause in weather-related fatalities.
Throughout history we, as humans, have a long history of altering our environment for our benefit and to make sure we have adequate food, shelter and water. Clearing and tilling land to plant crops, mining coal to be used for energy, and damming rivers to create freshwater lakes are all examples of this.
Inherently, these things are not particularly harmful for the environment on a small scale. However, the wheels of industry and ever-increasing economic growth have driven the magnitude of these endeavors and the subsequent production and release of carbon dioxide into the atmosphere.
A repercussion of all these changes in the environment has culminated in large phenotypic changes to Earth’s climate, which has been and still is unequivocally warming. Recent reports show that heat wave frequency, duration, season length and intensity are all increasing. These events have a direct impact on human health and physiology.
At the 2023 American Physiology Summit, game-changer session speaker Zac Schlader, PhD, discussed how agricultural workers and other manual laborers who work outside are often at greatest risk for and experience the worst of these heat-related effects.
Physiologically, extreme heat has detrimental effects to the entire body. But it seems to be particularly bad for the kidneys, as chronic kidney disease has been disproportionately seen in these populations. Older adults also have decreased ability to regulate their body temperature (thermoregulation), fluid regulation, and kidney and cardiovascular function, which leaves them more susceptible to heat-induced problems compared to young adults.
In animals, hyperthermia causes decreased food intake and lower reproduction rates, which, if left unchecked, can challenge a species’ reproductive capacity. Heat stress is particularly challenging for animals with few or no sweat glands, such as elephants and elephant seals. As temperatures increase, they become reliant on alternative methods of cooling such as water bathing and flipping cool sand on their backs to increase convective cooling.
If temperatures continue to increase, compensating for extreme heat may not be enough, and we may lose more species that make our beloved Earth so beautiful. If we don’t do something soon, such as putting strong policy changes into effect, we may not be able to prevent further increases in temperature and protect both humans and animals alike.
Dain Jacob is a PhD student at the University of Missouri in the Nutrition and Exercise Physiology Department. His research focuses on autonomic regulation of the peripheral vasculature and the impact of environmental stressors and sex hormones. Jacob served as a meeting blogger for the 2023 American Physiology Summit.