A new study published in Nature Reviews Earth & Environment warns that a third of the planet could become inhospitable to vulnerable populations if global temperatures rise more than 2°C above preindustrial levels.
The research, conducted by an international team of scientists, found that even young, healthy individuals would not be immune to extreme heat. The study highlights that an area equivalent to the size of the United States could become too hot for many to maintain safe body temperatures.
The study's findings underscore the urgent need to mitigate climate change and protect those most at risk. Lead author Dr. Tom Matthews, Senior Lecturer in Environmental Geography at King's College London, stated that "our findings show the potentially deadly consequences if global warming reaches 2°C." He added that prolonged outdoor exposure, even in the shade, with a strong breeze, and adequate hydration, could lead to lethal heatstroke.
The study also found that the portion of the planet deemed unsafe for older adults would increase by 35% if temperatures rise by 2°C. Meanwhile, the regions experiencing temperatures dangerous even for young, healthy individuals would triple.
The research integrated existing climate models with health data to assess rising temperatures against known heat mortality risks. Medical scientists have identified two key danger thresholds: uncompensable heat, where the body can no longer regulate its core temperature, and unsurvivable heat, where core body temperature reaches 42°C within six hours, causing fatal heatstroke.
The study found that between 1994 and 2023, only 2% of the planet exceeded the thermal tolerance threshold for people under 60, while 20% did so for those over 60. During that period, uncompensable heat levels were recorded for all age groups, but unsurvivable conditions occurred only for older adults, and only briefly.
If climate change leads to temperature increases of 4-5°C above preindustrial levels, vast portions of the globe would become uninhabitable. Under these extreme scenarios, 60% of the planet would surpass the uncompensable heat threshold for older adults, and even healthy young adults would face unsurvivable heat in some subtropical regions. The most affected areas would include Saharan Africa and South Asia.
Dr. Matthews emphasized the urgency of the findings, stating that "what our review really shows very clearly is that, particularly for higher levels of warming such as 4°C above the preindustrial average, the health impacts of extreme heat could be extremely bad." He added that at around 4°C of warming above preindustrial levels, uncompensable heat for adults would affect about 40% of the global land area, with only the high latitudes and cooler regions of the mid-latitudes remaining unaffected.
Extreme heat has already claimed over 260,000 lives since the year 2000. Nearly 200,000 of these deaths occurred during just three major heat waves. In 2003, 72,000 people died in Europe. In 2010, Russia saw 56,000 heat-related deaths. More recently, in 2022, another 62,000 people in Europe succumbed to extreme heat.
Dr. Matthews concluded that "interdisciplinary work is vital to improving our understanding of unprecedented heat's deadly potential and how it can be reduced." He also stressed the importance of providing reliable access to cooler environments to shelter from the heat as more of the planet experiences outdoor conditions too hot for human physiology.