RT Journal Article SR Electronic T1 The emergence of heat and humidity too severe for human tolerance JF Science Advances JO Sci Adv FD American Association for the Advancement of Science SP eaaw1838 DO 10.1126/sciadv.aaw1838 VO 6 IS 19 A1 Raymond, Colin A1 Matthews, Tom A1 Horton, Radley M. YR 2020 UL http://advances.sciencemag.org/content/6/19/eaaw1838.abstract AB Humans’ ability to efficiently shed heat has enabled us to range over every continent, but a wet-bulb temperature (TW) of 35°C marks our upper physiological limit, and much lower values have serious health and productivity impacts. Climate models project the first 35°C TW occurrences by the mid-21st century. However, a comprehensive evaluation of weather station data shows that some coastal subtropical locations have already reported a TW of 35°C and that extreme humid heat overall has more than doubled in frequency since 1979. Recent exceedances of 35°C in global maximum sea surface temperature provide further support for the validity of these dangerously high TW values. We find the most extreme humid heat is highly localized in both space and time and is correspondingly substantially underestimated in reanalysis products. Our findings thus underscore the serious challenge posed by humid heat that is more intense than previously reported and increasingly severe.