SCIENCE ADVANCES 2 August 2017

Eun-Soon Im,1* Jeremy S. Pal,2* Elfatih A. B. Eltahir3†

INTRODUCTION

The risk of human illness and mortality increases in hot and humid weather associated with heat waves. Sherwood and Huber (1) proposed the concept of a human survivability threshold based on wet- bulb temperature (TW). TW is defined as the temperature that an air parcel would attain if cooled at constant pressure by evaporating water within it until saturation. It is a combined measure of temperature [that is, dry-bulb temperature (T)] and humidity (Q) that is always less than or equal to T. High values of TW imply hot and humid conditions and vice versa. The increase in TW reduces the differential between hu- man body skin temperature and the inner temperature of the human body, which reduces the human body’s ability to cool itself (2). Because normal human…