Deadly Heat Stress Conditions Emerging

New study finds extreme heat and humidity events are already surpassing survivable thresholds

Apr. 9, 2026 at 6:39am

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A vast, atmospheric landscape painting in muted earth tones, with a shimmering mirage on the horizon conveying the overwhelming, sublime scale of extreme heat conditions.As the planet warms, deadly heat stress conditions are emerging with increasing frequency, posing grave risks to human health and survival.Phoenix Today

A new study led by researchers from the Australian National University and the University of Sydney has found that deadly heatwave events are occurring at temperatures and humidity levels previously thought to be survivable. The study examined six extreme heat events in locations around the world, including Mecca, Bangkok, Phoenix, Mount Isa, Larkana, and Seville, and found that non-survivable thresholds were surpassed in all of them.

Why it matters

This research highlights the growing threat of extreme heat and humidity driven by climate change, which can have devastating impacts on human health and survival, especially for vulnerable populations like the elderly, pregnant people, and those with underlying conditions. Understanding these new heat stress thresholds is crucial for developing effective adaptation strategies to protect communities.

The details

The study used the HEAT-Lim model, co-developed by researchers at the University of Sydney and Arizona State University, to analyze the heat events. This model demonstrated that deadly heat stress thresholds may be lower than the previously defined wet-bulb temperature of 35 degrees Celsius. In the events studied, top dry-bulb temperatures ranged from 41.53 degrees in Mount Isa to 46.73 degrees in Phoenix, while top wet-bulb temperatures ranged from 24.32 degrees in Phoenix to 30.85 degrees in Larkana. The researchers found that even extremely hot yet dry conditions can be just as deadly as hot and humid conditions.

  • The heatwave events analyzed occurred in Mecca (Saudi Arabia) during 2024, Bangkok (Thailand) during 2024, Phoenix (United States) during 2023, Mount Isa (Australia) during 2019, Larkana (Pakistan) during 2015, and Seville (Spain) in 2003.
  • All of the events were associated with at least 1,000 deaths, with the exception of the event in Australia.

The players

Professor Sarah Perkins-Kirkpatrick

Lead author of the study and researcher at the Australian National University and the ARC Centre of Excellence for the Weather of the 21st Century.

Professor Ollie Jay

Director of the Heat and Health Research Centre at the University of Sydney and co-developer of the HEAT-Lim model.

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What they’re saying

“While many people are rightly concerned about the possible effects of future heatwaves as global warming continues, our research shows that non-survivable conditions are occurring during present-day heat events.”

— Professor Sarah Perkins-Kirkpatrick

“The vulnerability of humans to extreme conditions will become more frequent as global warming continues. Adaptation initiatives against extreme heat and humidity are extremely important, including ensuring people have increased access to shade, buildings designed with cooling considerations, fans and interventions such as skin wetting.”

— Professor Ollie Jay, Director of the Heat and Health Research Centre at the University of Sydney

What’s next

The researchers plan to continue studying the impacts of extreme heat and humidity on human health and survival, with the goal of informing more effective adaptation strategies to protect vulnerable populations.

The takeaway

This study underscores the urgent need to address the growing threat of deadly heat stress conditions driven by climate change. Developing comprehensive adaptation measures, including improved access to cooling, shade, and other interventions, is crucial to safeguarding public health and saving lives in the face of these extreme weather events.