In the summer of 2021, 37-year-old ultra-marathon runner Philip Kreycik embarked on an approximately 8-mile run through Pleasanton Ridge Regional Park in California. Despite his experience, Kreycik left his phone and water in his car as temperatures soared into the 90s. Starting strong, he completed the first five miles quickly, but his pace slowed dramatically as the temperature climbed above 100 degrees Fahrenheit. He veered off the trail, and his steps became erratic. When he failed to return for a family lunch, his wife contacted the authorities. Tragically, it took over three weeks to locate his body, with an autopsy suggesting a heat-related medical emergency.
This incident highlights the lethal nature of extreme heat, which is increasingly turning ordinary activities into deadly endeavors.
Heat’s Deadly Reach
Extreme heat has claimed lives in various scenarios, including casual strolls, family hikes in national parks, outdoor concerts, and even within homes lacking air conditioning. During the 2023 Hajj pilgrimage in Mecca, approximately 1,300 people succumbed to temperatures exceeding 120 degrees Fahrenheit.
Heat waves are becoming more intense and prolonged due to human-caused climate change. The addition of humidity can push conditions to the brink of human survivability, overwhelming the body’s ability to adapt.
Understanding Heat’s Impact on the Body
Kreycik’s tragic story illustrates that even the fittest individuals are vulnerable to extreme heat. Scientists use environmental chambers to study how heat affects the body, examining responses to various temperature and humidity levels.
As temperatures rise, sweat glands work overtime to cool the body. However, high humidity can hinder this process, causing sweat to evaporate slowly or not at all. This inefficiency can lead to dehydration and an increase in body temperature.
The cardiovascular system is the first to react to heat stress. The heart pumps blood towards the skin to dissipate heat, often causing a flushed appearance. The hypothalamus, a small brain region, orchestrates the body’s cooling mechanisms. But extreme heat can disrupt this system, reducing blood flow to the brain and impairing cognitive function, leading to poor decision-making.
The Path from Heat Exhaustion to Heatstroke
Heat stress initially manifests as nausea, headaches, muscle cramps, and fainting—signs of heat exhaustion. Without intervention, it can progress to heatstroke, where the body’s cooling mechanisms fail entirely.
Heatstroke impairs mental capacity, making it difficult for individuals to recognize the danger they are in. Immediate treatment involves immersion in cold water or applying wet towels with fan assistance. Despite treatment, nearly 30% of heatstroke survivors may suffer permanent brain damage.
Facing a Hotter Future
While humans can acclimate to heat to a degree, extreme conditions can exceed our adaptive capabilities. Scientists use wet-bulb temperature—a measure that considers both temperature and humidity—to gauge heat stress. A wet-bulb temperature of 87.8 degrees Fahrenheit is near the limit of human survivability. Beyond this, the body struggles to cool itself effectively, posing severe health risks.
Understanding these dynamics is crucial as we navigate an increasingly hotter world, emphasizing the need for vigilance and proactive measures to mitigate the impacts of extreme heat.