A new study challenges the limits of survival and liveability in extreme heat.

In 2023, as record-breaking heatwaves dominate headlines, concerns about human survival in a warming world intensify. 

A new study by the University of Sydney and Arizona State University challenges existing thresholds for survivability in extreme heat, suggesting a potentially grimmer outlook than previously thought.

The commonly accepted 35 degrees Celsius wet-bulb temperature limit for human survival is deemed conservative in the report, as it overlooks individual variables and fails to account for real-world conditions.

Assoc/Prof Jennifer Vanos, the study's first author, says there is a need for a more nuanced approach.

“That number really oversimplifies what happens physiologically in the body when your body is exposed to that temperature, and it doesn’t account for other important variables like age or other vulnerability factors,” she said.

The study introduces a human-centric physiological model for assessing survivability and liveability in extreme heat, acknowledging the limitations of the existing wet-bulb temperature estimate. 

This measurement, in use for over a decade, assumes a person is indoors or shaded, unclothed, sedentary, fully acclimatised, and of average size, factors that often do not align with real-life scenarios.

Adjusting for humidity, age, activity level, and sun exposure, the research provides a range of safe wet bulb temperatures based on individual characteristics. 

Professor Ollie Jay from the University of Sydney says it is important to understand not just survival but the conditions that enable people to remain active and outdoors.

The study also suggests implications for the future, including the need for increased cooling infrastructure, personalised heat protection strategies, and potential heat-driven migration. 

The study is published in Nature Communications.