New research indicates that if global temperatures rise by 2 degrees Celsius above pre-industrial levels, vast areas – nearly as large as the United States – will be too hot for even healthy young adults to maintain a safe body temperature during extreme heat events. For individuals over 60, this 2-degree increase would mean that over a third of the Earth’s land area would surpass critical heat thresholds.
A team of international scientists, led by King’s College London, has shown that the ongoing global warming trend will result in more regions becoming dangerously hot for humans in the coming years.
The study, which appeared in Nature Reviews Earth and Environment, reveals that the land that could become too hot for healthy young adults (ages 18-60) to maintain safe core body temperatures would grow to approximately six percent of the Earth’s land area—which is roughly equivalent to the size of the United States—if global temperatures reach 2°C above pre-industrial levels.
Additionally, under these circumstances, the researchers predict that around 35% of land will pose a risk to those aged over 60.
Last year marked the first time the global average temperature exceeded 1.5°C above pre-industrial levels, and at the current pace of warming, we could reach 2°C by the mid-to-late century.
Dr. Tom Matthews, the lead author and a Senior Lecturer in Environmental Geography at King’s College London, stated: “Our results highlight the potentially fatal implications if global warming hits 2°C. The severe heat limits, which have only occasionally been surpassed for older adults in the hottest areas of the world, are likely to also affect younger adults. Prolonged exposure outdoors—even in the shade, with a good breeze, and when well-hydrated—could potentially lead to heatstroke, significantly increasing the risk of heat-related mortality.”
The research team compiled various scientific data to connect climate change with risks to human health, particularly focusing on ‘uncompensable’ and ‘unsurvivable’ heat thresholds. Scientists differentiate between these thresholds: ‘uncompensable’ means that a person’s core body temperature begins to rise uncontrollably, while ‘unsurvivable’ refers to scenarios where the core temperature reaches 42°C within six hours.
From 1994 to 2023, the combination of heat and humidity that humans cannot withstand was experienced on about 2% of the globe for adults younger than 60. More than 20% of the Earth’s land mass experienced these conditions for older adults, who are more susceptible to heat stress.
While all age groups have passed the uncompensable heat thresholds, unsurvivable thresholds have only been briefly exceeded for older adults.
In scenarios with increased warming of 4-5°C above pre-industrial levels, about 60% of the Earth’s surface could expose older adults to uncompensable heat during extreme events. At such temperature increases, younger adults in the hottest subtropical areas would also face the risk of unsurvivable heat.
Certain regions, including Saharan Africa and South Asia, are particularly vulnerable to crossing these critical temperature thresholds.
Dr. Matthews emphasized the importance of predicting the potential severity of future heat extremes and their impacts, stating it is essential for evaluating the costs of not addressing climate change and for directing adaptation strategies where they are most needed.
“What our study clearly illustrates is that at higher warming levels, such as 4°C above pre-industrial averages, the health impacts of extreme heat could be very severe,” he said.
“To better grasp the deadly potential of unprecedented heat and how to mitigate it, interdisciplinary collaboration is crucial. As more of the world faces outdoor conditions too hot for human biology, it is vital that people have dependable access to cooler spaces for relief from the heat.”
Since the year 2000, over 260,000 fatalities have been attributed to heat-related incidents, demonstrating that extreme heat already poses a significant risk to human life.
The three deadliest heat events in the 21st century resulted in nearly 200,000 deaths combined, including around 72,000 in Europe in 2003, another 62,000 in Europe in 2022, and roughly 56,000 due to the Russian heatwave in 2010.
This study also included contributions from Dr. Josh Foster of King’s College London and researchers from institutions such as the University of California, Stanford University, the NASA Goddard Institute for Space Studies, Columbia University, and Boston University.
