NASA’s Curiosity rover exploring Gale Crater on Mars has provided new details about how the ancient Martian climate went from potentially suitable for life—with evidence for widespread liquid water on the surface—to a surface that is inhospitable now.
Not far from our imagination, as the intensifying global warming on Earth continues, exceeding the 2°C warming threshold above pre-industrial levels could render vast portions of the planet uninhabitable due to extreme heat stress. A study from King’s College London warns that exceeding the threshold could render vast portions of the planet uninhabitable due to extreme heat stress.
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The paper finds that the amount of landmass on our planet that would keep a safe core body temperature will approximately triple—an area almost the size of the US—if global warming crosses 2°C above the pre-industrial average. The study underscores the increasing risks, particularly for older populations.
The researchers assessed heat mortality risks by examining two critical thresholds. The first, ‘uncompensable’ heat, occurs when the human body can no longer regulate its core temperature, leading to a dangerous rise in internal heat levels. The second, ‘unsurvivable’ heat, is defined as conditions in which a person’s core temperature reaches 42°C (107.6°F) within six hours, leading to lethal heat stroke even under shaded, well-ventilated, and hydrated conditions.
With 2024 already recording a global mean temperature surpassing 1.5°C above pre-industrial levels, scientists warn that the 2°C barrier could be breached by the mid-to-late 21st century. If warming reaches 4-5°C above pre-industrial levels, over 60% of the Earth’s surface could experience overheating conditions dangerous to older adults, said the study. Even younger adults may also face unsurvivable heat in the hottest subtropical regions, particularly in Saharan Africa and South Asia, according to the study published in Nature Reviews Earth and Environment.
Dr. Tom Matthews, the study’s lead author and a Senior Lecturer in Environmental Geography at King’s College London, highlighted the dire implications of these findings. “Our research demonstrates the potentially deadly consequences of surpassing the 2°C threshold. Historically, unsurvivable heat conditions have only occurred briefly and in limited regions for older adults, but our projections indicate that even younger populations will be at risk. Prolonged exposure under such extreme conditions, even with mitigating factors such as shade and wind, would likely lead to fatal heatstroke. This marks a significant escalation in heat-related mortality risks.”
The Deadly Reality of Extreme Heat
From 1994 to 2023, human thermal tolerances—defined as the combination of temperature and humidity beyond which the body cannot regulate heat—were exceeded in approximately 2% of the global land area for adults under 60. For older adults, who are more susceptible to heat stress, over 20% of the Earth’s land surface crossed this threshold.
Extreme heat events have already claimed more than 260,000 lives since 2000, highlighting the immediate threat posed by rising temperatures. The three deadliest heat waves of the 21st century—Europe’s 2003 and 2022 heatwaves and Russia’s 2010 event—collectively resulted in nearly 200,000 fatalities, including approximately 72,000 deaths in 2003, 62,000 in 2022, and 56,000 in 2010.
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While uncompensable heat thresholds have already been surpassed for all age groups, unsurvivable heat thresholds have so far only been exceeded briefly for older adults, said Dr. Matthews, emphasizing the urgent need for proactive mitigation efforts such as ensuring reliable access for all “to cool refugia” as the atmosphere threatens to increasingly overwhelm human physiology. “The costs of failing to mitigate climate change extend far beyond economic losses—they directly threaten human survival.”
Since extreme heat events become more frequent, without decisive action, large regions of the planet may become uninhabitable within this century.