Inside the Extreme Heat Lab: Simulating Our Deadly Climate Future
Journalist Graham Readfearn recently stepped into a simulation to investigate how the heatwaves of the future will impact the human body. As global heating accelerates due to fossil fuel burning, climate scientists warn that these extreme events are becoming more frequent, longer-lasting, and dangerously hotter.
Heatwaves on the Rise
Around the world, the climate crisis is already delivering more intense heatwaves. According to the medical journal The Lancet, heat extremes caused an estimated 546,000 deaths annually between 2012 and 2021—a staggering 63% increase compared to rates in the 1990s.
"That's the equivalent of a fully loaded jumbo jet full of people going down once every seven hours throughout the year," explains Professor Ollie Jay, director of the Heat and Health Research Centre at the University of Sydney. "And the really important thing to keep in mind is that every heat-related death is preventable."
The Thermal Ergonomics Laboratory
Professor Jay's centre houses the Thermal Ergonomics Laboratory, a chamber the size of a large bedroom where temperature and humidity can be precisely controlled. This facility allows researchers to study the physiological effects of extreme heat in a controlled environment.
Readfearn, with his 51-year-old body, entered the climate room twice to experience conditions projected for a world warmed by 2°C—a scenario that might be just decades away.
What Extreme Heat Does to Your Body
In the first experiment, the chamber was set to 43°C with 18% humidity—conditions expected to become common in cities like Sydney, Mexico City, and São Paulo. Afterward, Professor Jay explained the critical factors often overlooked when discussing hot weather.
"Most people don't realise that temperature is measured in the shade," he noted. "If you're in direct solar radiation, the heat stress on your body is much greater." This is why the lab uses heat lamps to mimic sunlight.
Humidity plays an equally crucial role. "The only way your body can physiologically keep cool is by producing sweat," Jay explained. "But it's not the production of sweat that cools you down—it's the evaporation. Humidity prevents that evaporation, even at the same ambient temperature."
The Humidity Factor
For the second experiment, Readfearn experienced the same 43°C temperature but with higher humidity at 36%. While this relative humidity might not sound extreme, at such high temperatures, it means significant moisture in the air since warmer air can hold more water.
Under these conditions, sweating becomes ineffective for cooling. The "feels like" temperature exceeded 49°C (120°F), demonstrating how humidity dramatically increases heat stress.
Physiological Impacts
The extreme heat forced Readfearn's heart to work overtime, caused weight loss through sweating, and raised his core body temperature—changes he wasn't consciously aware of during the experiment. If trapped in such conditions without relief, these physiological responses could prove deadly as the body loses its ability to compensate and cool itself.
Beyond Mortality Statistics
Professor Jay emphasizes that heatwaves impact more than just mortality rates. "It's also about the way heat affects people's ability to carry out daily activities," he said. "This is a real problem for workplaces, particularly when people cannot escape extreme heat conditions. It impacts our ability to be productive and safe."
Extreme heat has been linked to increased risks of stillbirths, low birth weights, and heightened vulnerability for infants, the elderly, and those with pre-existing conditions like heart or kidney disease.
"There are all these different types of impacts on human health and wellbeing that aren't necessarily captured in mortality statistics," Jay added.
An Escalating Threat
With global heating continuing unabated, such dangerous heatwaves—and their direct risks to human health—will become increasingly common. "It is very plausible that those impacts are just going to escalate," Professor Jay warned. "In fact, it's pretty much almost certain, unless we figure out a way to mitigate climate change more effectively."
The research underscores that while the future may bring more extreme heat, the human toll remains preventable through both climate action and adaptive measures to protect vulnerable populations.
