How hot is too hot for the human body? (2023)
Scientists have identified the human body's survival limit is likely when combined heat and humidity, measured by "wet-bulb temperature," exceeds 35°C, as the body can no longer cool itself through sweating, leading to heatstroke and organ failure.
Background
- This 2023 article explores "wet-bulb temperature" (Tw), a measure combining heat and humidity. The critical limit for a healthy young adult is a wet-bulb temperature of 35°C (95°F) — beyond that, the body can no longer cool itself by sweating, leading to fatal overheating within hours.
- Actual deaths occur at lower thresholds, especially for the elderly or those with health conditions. The 2021 Pacific Northwest heatwave saw mass casualties at wet-bulb temps far below 35°C.
- Climate change is making extreme heat-humidity events more frequent. Parts of South Asia, the Persian Gulf, and the US Southwest are already brushing against or exceeding survivable limits for brief periods.
- Researchers stress that official heatwave warnings often lag behind the physiological reality, and that infrastructure (AC, cooling centers, urban design) is unevenly distributed, making heat a deadly inequality issue.