Essay by Eric Worrall

“… the upper limits of human heat tolerance were breached for a total of 43 hours over the six days of Hajj. …”

More than 1,300 Hajj pilgrims died this year when humidity and heat pushed past survivable limits. It’s just the start

Published: December 19, 2024 6.08am AEDT
Emma Ramsay Research Affiliate in Climate Adaptation, Monash University
Shanta Barley Adjunct Lecturer in Ecology, The University of Western Australia

Every year, hundreds of thousands of Muslims undertake the Hajj –the sacred pilgrimage to Mecca. In 2024, the pilgrimage took place in mid-June, the start of the Saudi summer. 

But this year, more than 1,300 pilgrims never made it home. Lethal heat combined with humidity proved deadly.

Our new research shows the upper limits of human heat tolerance were breached for a total of 43 hours over the six days of Hajj. During these periods, heat and humidity passed beyond the point at which our bodies are able to cool down. 

Scientists are increasingly worried about the death toll caused by humid heatwaves, and how it will escalate in the near-term. This year is now the hottest year on record, overtaking the previous hottest year of 2023.

…

This year’s pilgrimage started on June 14. Over the next six days, the temperature topped 51°C, while “wet-bulb temperatures” (the combination of temperature and humidity) rose as high as 29.5°C. 

…

Read more: https://theconversation.com/more-than-1-300-hajj-pilgrims-died-this-year-when-humidity-and-heat-pushed-past-survivable-limits-its-just-the-start-245271

The abstract of the study;

• Comment
• Published: 18 December 2024

Humid heat exceeds human tolerance limits and causes mass mortality

• Tom Matthews, 
• Emma E. Ramsay, 
• Fahad Saeed, 
• Steven Sherwood, 
• Ollie Jay, 
• Colin Raymond, 
• Nerilie Abram, 
• Jason Kai Wei Lee, 
• Shanta Barley, 
• Sarah Perkins-Kirkpatrick, 
• Mariam Saleh Khan, 
• Katrin J. Meissner, 
• Callum Roberts, 
• Dileep Mavalankar, 
• Kenneth G. C. Smith, 
• Atta Ullah, 
• Anwar Sadad, 
• Victoria Turner & 
• Andrew Forrest 

Nature Climate Change (2024)Cite this article

The hottest boreal summer on record has driven widespread humid heat mortality across every continent of the Northern Hemisphere. With critical physiological limits to human heat tolerance drawing ever closer, this Comment highlights the urgent need to limit further climate warming and emphasizes the adaptation challenge ahead.

Read more: https://www.nature.com/articles/s41558-024-02215-8

The wet bulb limit claim is nonsense.

When I was young, one of my first jobs was working in a poorly ventilated plastic factory. My fellow workers were a pregnant South Sea Islander and a bunch of chain smoking elderly East Europeans who used to smuggle vodka into the lunch room.

During Summer the temperature on the factory floor regularly hit 55C (130F). The factory was extremely humid, not only did the decrepit hot presses release huge amounts of steam, the chemical processes also released lots of water vapour. You could see visible clouds of steam hovering around the work area, everything was dripping wet. The work was physically demanding, continuously moving material by hand and operating a heavy hot press lever.

It was the strangest experience walking out into a 110F day at the end of my shift, and shivering with cold for two minutes while my body adjusted to outdoor temperatures.

I don’t know what the wet bulb temperature on that factory floor was, but on the hottest days all the managers played serving maid, offered us rehydration drinks every 5 minutes. They were probably breaching some workplace health and safety law operating in those temperatures, and wanted to make sure none of us dropped dead.

So what happened to those Hajj pilgrims?

Obviously we can only speculate, but it seems much more likely the pilgrims died from dehydration and neglect, or didn’t give themselves enough time to adapt to the heat.

You can’t walk into the extreme conditions I just described, or the extreme conditions of an Arabian Summer, and expect to feel fine immediately. You have to build up hot weather tolerance the same way you build altitude tolerance when preparing for extreme mountain climbing. Hajj pilgrims who just flew in from colder countries without giving themselves time to adapt would have severely stressed their bodies the moment they set foot outside the airport.

In addition, to survive such heat you have to consciously remind yourself to drink regularly – if you wait until you feel thirsty, your body is already in trouble. Those managers in that factory I described were offering rehydration drinks every 5 minutes because that is what your body needs in such conditions, it is easy to become distracted and forget to take care of yourself. You also need well balanced drinks, an electrolyte imbalance is lethal in such conditions – drinking soda cans or anything other than a well balanced rehydration drink, you could suffer a health crisis within hours if you don’t take proper care of yourself.

My grandpa who worked in even more extreme conditions in a WW2 steel foundry told me how managers walked the factory floor making sure everyone took salt pills, to prevent workers from fainting.

I’m sure the locals know how to survive, this is where they live – they would have learned as kids how to survive in such a climate. But people who aren’t used to such conditions, or who get caught up in the moment and forget to drink water, it’s no different to someone who lives in a temperate climate visiting somewhere really cold in winter. If you don’t know and rigorously follow the rules, if you don’t take care of yourself, you could lose your life.