Heat Pushes Human Limits: How It Claims Lives
In the summer of 2021, a 37-year-old ultra-marathon runner mapped out an 8-mile loop in California's Pleasanton Ridge Regional Park using an app. On July 10, as temperatures climbed into the 90s, Kreycik left his car without his phone or water and set off at a fast pace, completing the first 5 miles in under six minutes each. However, things took a turn for the worse. GPS data showed he slowed down dramatically, veered off the trail, and his steps became erratic. By then, the temperature had surpassed 100 degrees Fahrenheit.
When Kreycik didn't show up for a family lunch, his wife alerted the police. It took over three weeks to locate his body. An autopsy revealed no traumatic injuries, and police confirmed that Kreycik likely suffered a heat-related medical emergency. This tragedy, unfortunately, is not isolated; extreme heat is turning everyday activities into life-threatening events.
People have perished while taking midday strolls, hiking in national parks, attending outdoor concerts, and even while at home without air conditioning. During the June Hajj pilgrimage, around 1,300 people died as temperatures soared above 120 degrees Fahrenheit in Mecca. Heat is the deadliest form of extreme weather, and the human-induced climate crisis is intensifying heat waves, making them more severe and prolonged. Humidity exacerbates these conditions, pushing them to the brink of human survivability.
"We've essentially weaponized summer," stated Matthew Huber, a climate professor at Purdue University.
Inside a Heat Chamber
Despite being an extremely fit and experienced runner, Kreycik was not immune to the dangers of extreme heat. Vulnerability to heat varies, but no one, not even top athletes, is entirely safe. As the Olympic Games began in Paris, many athletes were anxious about the forecasted temperatures exceeding 95 degrees.
Scientists are still unraveling how heat affects the body using environmental chambers, which simulate various temperature and humidity conditions. CNN visited one such chamber at the University of South Wales in the UK to understand how heat kills in a controlled environment.
"We'll warm you up and things will slowly start to unravel," warned Damian Bailey, a physiology and biochemistry professor at the university. Bailey monitors vital signs like heart rate, brain blood flow, and skin temperature as subjects rest or perform light exercise. Starting at a comfortable 73 degrees Fahrenheit, the temperature ramps up to 104 degrees, with humidity rising from a dry 20% to a stifling 85%.
"That's the killer," Bailey noted. "It's the humidity you cannot acclimatize to." This is when things get challenging.
Effects of Heat on the Body
Skin: Sweat glands produce sweat to cool the body, but excessive heat and humidity disrupt this process. Over-sweating leads to dehydration, and the body may not signal the need for fluids until it's too late. High humidity prevents sweat from evaporating, pooling on the skin, and leading to a dangerous rise in body temperature.
Heart: In extreme heat, the heart works harder to maintain body temperature by pumping blood toward the skin to release heat. This process, combined with fluid loss from sweating, forces the heart to work even harder, sometimes feeling like it's "thumping out of your chest."
Brain: The hypothalamus regulates the body's cooling response, but in extreme heat, its function deteriorates. Blood flow to the brain decreases, affecting cognitive abilities, worsening mental health conditions, and leading to poor decision-making.
How Heat Kills
Heat can quickly escalate from uncomfortable to deadly. Initial symptoms include nausea, headaches, muscle cramps, and fainting, indicating heat exhaustion. If untreated, heatstroke can follow, where the body's cooling mechanisms fail, and core temperature rises above 104 degrees Fahrenheit. This can lead to disorientation, loss of consciousness, organ failure, and eventually death. Immediate treatment involves immersion in cold water or placing wet towels on the body.
A Deadlier Future
Our bodies can adapt to heat to some extent, but extreme conditions can be too severe to handle. Scientists use wet-bulb temperature, accounting for both temperature and humidity, to gauge heat stress. A wet-bulb temperature of around 87.8 degrees is near the human survivability limit. As global warming progresses, billions will face dangerous heat levels, especially in densely populated regions with limited access to air conditioning.
Even wealthier countries will not be spared. Extreme humid heat will affect parts of the US, including the Midwest. Future summers will likely be hotter than current standards, with extreme heat persisting into the night, depriving bodies of recovery time. Successive heat waves will become more common, amplifying the threat.
The World Health Organization estimates that heat kills 489,000 people annually, though the true toll may be higher due to underreporting. Heat-related deaths are often misattributed to other causes like heart attacks or strokes.
Heat's impact is subtle but deadly, lacking the immediate destruction of hurricanes or floods. It is a silent, invisible killer, causing irreversible damage to our bodies. The tragic, preventable deaths of people like Philip Kreycik highlight the urgent need for action against extreme heat.