Deadly Heatwaves Strike at Lower Temperatures Than Previously Thought, New Study Reveals
A new international research paper, led by The Australian National University (ANU) and the University of Sydney, has delivered a stark warning: deadly heatwaves are already occurring at temperatures and humidity levels previously considered survivable for humans.
"Non-survivable thresholds were exceeded in all six cases."
The Study
Published in Nature Communications under the title "Deadly heat stress conditions are already occurring", the research redefines the limits of human endurance. The team, led by Professor Sarah Perkins-Kirkpatrick, analyzed six extreme heatwave events between 2003 and 2024:
- Mecca, Saudi Arabia (2024)
- Bangkok, Thailand (2024)
- Phoenix, United States (2023)
- Mount Isa, Australia (2019)
- Larkana, Pakistan (2015)
- Seville, Spain (2003)
All six events featured extreme climatological conditions. With the exception of Mount Isa, each event was linked to at least 1,000 deaths.
Challenging the Survivability Threshold
Historically, the conventional "survivability limit" for human heat stress was defined by a wet-bulb temperature of 35 degrees Celsius. This new study challenges that benchmark.
Using the HEAT-Lim model (co-developed by the University of Sydney and Arizona State University), researchers found that environmental heat stress thresholds may be significantly cooler and drier than previously understood when accounting for human physiological limitations.
The six events recorded wet-bulb temperatures well below 35°C. Despite this, deadly thresholds were regularly exceeded—especially for older individuals directly exposed to the sun. The research also found that extremely hot but dry conditions can be as lethal as hot and humid conditions.
Recorded Temperature Ranges- Dry-bulb temperature peaks: 41.53°C (Mount Isa) to 46.73°C (Phoenix)
- Wet-bulb temperature peaks: 24.32°C (Phoenix) to 30.85°C (Larkana)
Populations at Highest Risk
Individuals aged 65 and over face a high risk of physiological heat stress during heatwaves in the Middle East, Southern Asia, Central America, Australia, and India/Pakistan. This risk applies unless they have consistent access to shade or active cooling methods.
The Path Forward: Adaptation and Mitigation
Professor Ollie Jay, Director of the Heat and Health Research Centre at the University of Sydney, emphasized that human vulnerability to extreme conditions is projected to increase as global warming continues.
He highlighted critical adaptation strategies, including:
- Increased access to shade
- Cooling-focused building designs
- Use of fans
- Interventions such as skin wetting
"These measures are considered particularly critical for vulnerable populations."
This includes the elderly, pregnant individuals, young children, people with chronic health conditions, and those with limited economic access to adequate cooling.