 This study applies physiological and biophysical principles to improve current estimates of survivability and introduce livability limits under extreme heat conditions, showing that the 35°C wet bulb temperature threshold used in most studies is a vast underestimation of risks in hot dry conditions. The study shows that updated survivability limits correspond to TW 25.8-34.1°C, young, and 21.9-33.7°C old, which are 0.9-13.1°C lower than TW equals 35°C, with even greater reductions for older female adults in dry conditions. The study also shows that livability declines with sun exposure and humidity, yet most dramatically with age, indicating a stronger impact from aging than warming on safe activity levels for younger and older adults. This article was authored by Jennifer Vanoes, Dizelle Guzmanich-Avaria, Jane W. Baldwin, and others. We are article.tv, links in the description below.