How does extreme heat affect your body? - Carolyn Beans

The year is 2050, and it seems like every morning is starting off on the wrong foot. School is closed for yet another heat day, forcing the kids to stay home while the air conditioning continues to run full blast. Your regular babysitter can’t make it because the intense heat has warped the rails for their commuter train. To add salt to the wound, your dog is practically begging for a walk, but the pavement is scorching enough to cause third-degree burns to anyone brave enough to touch it.

This scenario is a harsh reality in many parts of the world. On average, heat waves are becoming more frequent, lasting longer, and hitting harder. A projection made in 2022 suggests that by 2050, Earth’s mid-latitudes could endure extreme heat for between 90 and 180 days each year. Tropical regions could face even greater challenges. So, the question arises: how hot is too hot, and what measures can people take to cope with the heat?

The human body possesses an incredible ability to manage temperature; however, our cooling mechanisms are only effective under optimal conditions. When air temperatures rise, the hypothalamus signals blood vessels near the skin to widen, allowing for a greater flow of blood close to the body's surface, which helps to release excess heat. This hormonal reaction also activates our sweat glands. As sweat evaporates, it draws heat away from our skin. Yet, when humidity levels spike, evaporation slows down, and sweating becomes ineffective.

To gauge humidity, scientists employ a metric known as wet-bulb temperature. This entails wrapping a wet cloth around a thermometer to test whether evaporation can lower the temperature reading. If it can’t, it indicates that conditions are too humid for sweat to cool us down efficiently. A wet-bulb temperature of approximately 35°C is seen as the survival limit for humans, although temperatures at this level aren’t commonly reached.

The US National Weather Service utilizes the interaction between humidity and air temperature to formulate the heat index. As both metrics escalate, the heat index does too. Heat is deemed dangerous once the index surpasses 39.4°C (or 103°F), but even lower heat indexes can pose risks when sustained over several days. A heat wave is classified as a sequence of two or more days of unusually high temperatures for a specific place and time. For instance, a consecutive run of 32°C days in Houston, Texas, is typical during summer, but would be considered a heat wave come March.

These heat events impact almost every corner of daily life. Picture a heat wave hitting a tropical city in June. The immediate fallout affects outdoor workers, whose excessive sweating can lead to dehydration and heat cramps. If they push through, they risk worsening into heat exhaustion or, more alarmingly, heat stroke— a serious condition where body temperature soars past 40°C. As emergency calls increase across the city, vulnerable groups such as children, the elderly, and pregnant individuals are most at risk.

Alongside the strains on individuals, the heat escalates hospital visits related to heart, kidney, and lung conditions, resulting in a flood of patients that may overwhelm healthcare providers. As the week progresses, the city slows to an agonizing pace. Schools and construction sites shutter, while airlines have to limit their weight capacity for takeoff, leaving countless travelers stranded. Additionally, kitchens in restaurants can become intolerable, causing many to close their doors.

For residents fortunate enough to stay indoors with air conditioning, safety is achievable. Yet, constant reliance on AC systems doesn't come without a cost. Many families find themselves in a difficult predicament, having to choose between staying cool or affording meals. Moreover, if heat waves persist, the strain on the power grid could lead to city-wide outages.

The repercussions are profoundly real; approximately 500,000 individuals die annually due to extreme heat, and these conditions are becoming alarmingly frequent. To mitigate the health fallout, it’s essential to seek help for heat-related issues, stay hydrated, and ensure public access to water and air conditioning. Never let anyone convince you that a slight temperature increase— just 1 to 2 degrees— doesn’t carry significance. Such a change can significantly alter our very way of life.