Six ‘Non-Survivable’ Heatwaves

Earlier this year, scientists examined a critical question: at what level of heat does a large number of deaths occur? In a paper published in the journal Nature, titled “Deadly heat stress conditions are already occurring,” they analyzed six events in which hundreds — and in some cases thousands — of people died due to extreme heat. By examining these events, the authors believe they can, with some precision, identify the conditions under which extreme heat becomes life-threatening. What makes this especially troubling is that these six events are not the only instances of “non-survivable” heat in recent history — and the problem will only grow more widespread as the Earth continues to warm.

The six heatwaves studied were:

• Middle East, June 2024 (around Mecca during Hajj): More than 1,300 pilgrims died. Many were elderly and had walked long distances.
• South Asia, April 2024 (Bangkok and surrounding areas).
• North/Central America, July 2023 (Phoenix, Arizona area): An extended period during which temperatures exceeded 100°F for many consecutive days.
• Australia, January 2019 (Mount Isa).
• India/Pakistan, May–June 2015 (Larkana/Karachi).
• Europe, August 2003 (areas around Seville): More than 70,000 excess deaths were recorded, primarily among older adults.

The study found that among older adults, organ failure often began after six hours of sun exposure in 35°C (approximately 99°F) heat. The researchers also examined the role of humidity, concluding that dry heat is nearly as dangerous as humid heat.

Among their most troubling conclusions, the authors told The Guardian: “Much of the world’s population lives in these places. Global warming will really hurt if it goes too much further, just due to the extreme temperatures and humidity — even if we manage rainfall, aridity, storms, and sea level changes.”

The study also highlighted that the danger threshold varies widely depending on heat and humidity levels, and it did not account for the additional, deadly effects of air pollution.

One recent examination of air pollution’s compounding dangers appeared in a New York Times article about one of the largest, hottest, and most polluted cities in the world. New Delhi, India’s capital, has a metropolitan population of 30 million people. The Times reported that experts at the country’s leading research hospital describe the air as “severe and life-threatening,” with toxic pollutant levels — from cars, factories, and crop-waste burning — reaching as much as 20 times above safe breathing thresholds. Temperatures in the city have exceeded 110°F on multiple occasions; the record, set on June 2, 2024, reached 49.1°C (approximately 120°F).

Public health officials have established guidelines for when temperatures become dangerous, and these thresholds are broadly consistent across most developed nations. The National Weather Service publishes a chart titled “Possible heat disorders for people in high risk groups,” which identifies 90°F as the threshold for extreme heat. At that level, people may begin to experience sunstroke, muscle cramps, and heat exhaustion with prolonged exposure or physical activity. Above 105°F, the risks become significantly more severe, with heatstroke becoming possible — and, in some cases, fatal.

A look at Zoom Earth‘s real-time global temperature map reveals that temperatures exceed 90°F across parts of Africa, Southeast Asia, and Australia on any given day. The map makes the breadth of this danger impossible to ignore.