The unstoppable global warming will cause more parts of the planet to become uninhabitable and excessively hot for the human body in the coming decades.
A recent study published in the journal *Nature Reviews Earth and Environment* reveals that the amount of land surface that will be too hot even for *young and healthy humans* (between 18 and 60 years old) to maintain a *safe core body temperature* will approximately triple (up to six percent), an area nearly the size of the United States, if global warming reaches *2°C above pre-industrial levels*.
Under these conditions, they also warn that the land surface where people over 60 will be at risk will increase to nearly 35%.
## An Uncertain Future and Uninhabitable Zones
Last year was the first calendar year with a *global average temperature* exceeding 1.5°C above pre-industrial levels, and at the current rate of warming, we could reach 2°C by mid or late century.
Dr. Tom Matthews, lead author and professor of Environmental Geography at King’s College London, highlights in a statement: “Our findings show the *potentially deadly consequences* if global warming reaches 2°C.”
“It is likely that insurmountable heat thresholds, which until now have only been briefly exceeded for the elderly in the warmest regions of the Earth, will emerge even for younger adults.”
“In such conditions, prolonged outdoor exposure, even for those in the shade, exposed to a strong breeze, and well hydrated, would lead to a lethal heatstroke. It represents a drastic shift in the *heat-related mortality risk*.”
For their assessment, the team gathered scientific findings to link the physical climate science with heat-related mortality risk, including crossing “uncompensable” and “unsurpassable” thresholds.
Scientists distinguish between *uncompensable thresholds*, beyond which the human core body temperature increases uncontrollably, and *unsurpassable thresholds*, where the body’s core temperature reaches 42°C within six hours.
## Future Perspectives
Between 1994 and 2023, *human thermal tolerances*, the combination of temperature and humidity above which the human body cannot cope, were exceeded on approximately 2% of the world’s land surface for adults under 60. Over 20% of the Earth’s land surface crossed this threshold for the elderly, who are *more vulnerable to heat stress*.
Although uncompensable thresholds have been exceeded for all ages, unsurpassable thresholds have only been briefly exceeded for the elderly so far.
If warming rises by 4 to 5°C above *pre-industrial levels*, the elderly could experience unbearable heat over about 60% of the Earth’s surface during *extreme events*.
At that level of warming, unbearable heat would also start to become a threat for younger adults in the *warmest subtropical regions*. Some regions are at a higher risk of crossing critical thresholds of uncompensability and unsurpassability, with populations in the Saharan Africa and South Asia being the most endangered.
Dr. Matthews comments that anticipating the magnitude of *future extreme heat events* and their worst effects is essential to understand the costs of not mitigating climate change. It is also crucial to guide adaptation efforts to the most vulnerable communities.
“What our analysis very clearly shows is that, particularly in the case of higher warming levels, such as 4°C above *pre-industrial levels*, the effects of extreme heat on health could be extremely severe,” he states.
With warming around 4°C above pre-industrial levels, the uncompensable heat for adults would render around 40% of the *land surface* uninhabitable, with only high latitudes and the coldest regions of mid-latitudes remaining unaffected.
“Interdisciplinary work is crucial to enhance our *understanding of the unprecedented lethal potential of heat* and how to reduce it. As more parts of the planet experience outdoor conditions too hot for our physiology, it will be essential for people to have reliable access to cooler environments to *protect themselves from the heat*,” he concludes.
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