Deadly heat stress conditions are already occurring

This study challenges the long-standing assumption that human survivability limits occur at a wet-bulb temperature of 35°C. Using the physiology-based HEAT-Lim model, it finds that dangerous and even non-survivable heat conditions can occur at lower temperatures and in drier environments than previously understood. Analysis of six historical heat events shows that deadly thresholds are already being exceeded under present-day conditions, particularly for older populations exposed to outdoor heat. The findings also demonstrate that extreme dry heat can be as dangerous as humid heat. Overall, the study highlights the need for more accurate, physiology-based approaches to better assess and anticipate heat-related risks.