The unstoppable global warming will cause more parts of the planet to become uninhabitable zones 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 triple approximately (reaching about six percent), an area almost the size of the United States, if global warming reaches 2°C above pre-industrial levels.
Under these conditions, it is also warned that the land area where people over 60 years old will be at risk will increase to about 35%.
An Uncertain Future and Uninhabitable Zones
Last year was the first year with a global average temperature above 1.5°C compared to pre-industrial levels, and with the current rate of warming, it could reach 2°C by mid or late this 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 limits, which have so far only been briefly exceeded for older adults in the hottest regions of the Earth, will even arise for younger adults.”
“In these conditions, prolonged outdoor exposure, even for those in the shade, exposed to a strong breeze and well hydrated, is expected to cause lethal heatstroke. It represents a drastic shift in the risk of heat-related mortality.”
For their assessment, the team gathered scientific findings to link physical climate science with the risk of heat-related mortality, including the crossing of “incompensable” and “insurmountable” limits.
Scientists distinguish between incompensable limits, beyond which human core body temperature increases uncontrollably, and insurmountable limits, 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 about 2% of the global land surface for adults under 60 years old. Over 20% of Earth’s land surface has exceeded this limit for older adults, who are more vulnerable to heat stress.
Although incompensable limits have been exceeded for all ages, insurmountable limits have so far only briefly been exceeded for older adults.
If warming increases by 4 to 5°C above pre-industrial levels, older adults may experience unbearable heat on about 60% of Earth’s surface during extreme events.
At this level of warming, unbearable heat would also begin to pose a threat to younger adults in hotter subtropical regions. Some regions are at higher risk of exceeding critical incompensability and insurmountability limits, and the populations of the African Sahara and South Asia are among the most vulnerable.
Dr. Matthews comments that anticipating the magnitude of upcoming extreme heat events and their worst effects is essential for understanding the costs of not mitigating climate change. It is also crucial for guiding adaptation efforts to the most vulnerable communities.
“What our analysis very clearly shows is that, especially in the case of higher levels of warming, such as 4°C above pre-industrial levels, the effects of extreme heat on health can be extremely severe,” he states.
With warming of about 4°C above pre-industrial levels, unbearable heat for adults would make about 40% of the land surface uninhabitable, and only higher latitudes and colder regions of mid-latitudes would remain untouched.
“Interdisciplinary work is vital to improve our understanding of the unprecedented lethal potential of heat and how to reduce it. As more parts of the planet experience very hot outdoor conditions 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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