If anyone hasn't already, you should read the opening to Kim Stanley Robinson's Ministry for the Future that imagines how this particular scenario would go. It's a terrible glimpse of things to come.
this post was submitted on 12 Apr 2025
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As far as I can tell, this same research methodology would say that humans can't survive temperatures below 18 degrees Celsius. Put someone in a small room and tell them not to do anything useful to solve their problem, and they're going to do very poorly.
We are defined by our tool use, and not being able to survive the outdoors without wearing anything to suit the local environment is pretty common across the world.
So what do you wear to survive lethal wet bulb temperatures for a couple of days? As a rural third worlder with no access to power or air conditioned spaces?
You don't have to live in the third world to lack access to A/C either. Just being poor is enough in some places, and other places, even if they could afford it, may not have ever thought of it that now will. The American Northwest had that stint of temperatures a few years back that were causing all sorts of trouble, and part of the issue was people who had only heating because it wasn't normal to get that hot.
I would go in a basement, or a hole in the ground, or swim in a river or in the ocean, or find some wind while pouring more water on myself to complement the sweat.
The latter doesn't work for lethal wet bulb temperatures.
Actually it does work because the 'lethal" wet bulb temperatures are below human body temperature, so wind and extra water do indeed bring down the skin temperature, just less effectively. Now if the wet bulb temperature rises above body temperature it's a different story and it's significantly above lethal wet bulb temperature.
Please reread https://www.pnas.org/doi/10.1073/pnas.2421281122
Perspiration does not cool down at lethal wetbulb so wetting the body with ambient temperature water does not help since there is no evaporation enthalpy. Forced convection air buys you almost nothing. Immersion in ambient temperature water, especially agitated, buys you a few degrees higher tolerance due to its higher heat capacity.
Retreating underground into previously prepared subterraneous shelters would help. Starting digging too late will just give you a heat stroke from physical exertion.
Realistically, lethal wet bulb spell of a few days in an unprotected population is a mass casualty event. Given that grid failure is likely under the circumstances, the size of the unprotected population is larger than many expect.
"Just give you a heat stroke from physical exertion" I wonder how many lives can be saved by a someone with a powered excavator (likely diesel) digging a trench so that people can access fresh cool earth at the bottom of the trench
I'm looking at
suggesting that humans cannot effectively thermoregulate in wet bulb temperatures (Twb) above 26 to 31 °C, values considerably lower than the widely publicized theoretical threshold of 35 °C
And I'm thinking that showering or swimming in water at 31°C is considered "quite hot" and is representative of ocean water temperatures in some tropics like in Oceania.
I researched a bit further and swimmers have died racing swimming in hot water, but possibly idling in hot water might give about 1-2°C margin of survivability compared to sweating in a wetbulb heatwave on land.
However swimming pools are very often built underground in the style of an open top basement, and water often comes from wells, so I still think there's some chances of surviving with the help of water.
Now when ground temperatures rise above that lethal temperature, everyone without a heat pump is going to die.
Yeah, I hate when the temperature falls below 18 degrees Celsius! There have been times when I've gotten so uncomfortable that I've had to put some pants on. It's possible to survive it, for sure, but it sucks.
EDIT: I finally found the answer. The article is talking about 31°C wet bulb temperatures, which is equivalent to 100% rH.
At 100% rH, 31°C is a heat index temperature of 49°C (120°F or 322k).
So if it hits 49°C at ~33%rH you might want to turn up the aircon a notch.
~~So 31c at checks notes 92% rH? Wow I sure am worried now!~~
~~Even in the eternally damp UK rn the rH is 31% and at that level it'd need to be 41c before it causes any problems at all~~
~~This tracks with my personal experience where 30-35c feels pretty warm but not too warm for a nice summer day. Past 35c I'd avoid public transport and maybe wear white and would probably keep a fan going indoors occasionally~~
~~Am I wrong? Please dunk on me if I just don't get it, because otherwise I feel like this article is kind of misleading~~
As someone having tried 48-49°C and somewhere around 20-30% I would not recommend. I sure prefer -35°C. I mean if I have to choose.
The article is not misleading, it's simply stating/confirming the known facts (the temperature at which vital proteins in our bodies start to degrade is very well known, feaver is the name).
Your assumption is that you may never face extreme conditions which may be right - climate change in its core is a chaotic process. That still doesn't mean that conditions won't rise to levels where younger and older and weaker persons - who have a much smaller frame of acceptance for higher physiological stress levels - aren't affected. The people in the test were young and healthy - well, guess what, that's not everyone.
So you are right but you don't account for or care for significant numbers of your countrymen. That's ok but it narrows the broader picture we need to look at as a civilisation.
I'm trying to understand what exactly those conditions are more than anything. The articles frames the findings as temperatures of 31c breaking down important proteins in the human body to ill effect, but this cannot be true because there are many regions in the world where temperatures stay up even higher for prolonged periods of time and yet the people that inhabit them are completely fine.
We also know that humidity levels in a given temperature actually impact significantly how we experience it and what the health risks are, due to our bodies' evaporative cooling.
What I don't seem to see in the article are specifics, what is the rH % at which 31c has such a negative effect? What rH % is a "wet bulb" temperature equivalent? In human terms, what temperature per rH % did these experiments find to be harmful? Because as I described, 31c at 33% rH does not even feel that warm, nevermind harmfully hot.
I have tried googling this as well but I think I'm just not phrasing it correctly or the question I'm asking is so stupid and obvious that there's no actual written answer.
Here's a book that dives very deep into the topic:
https://en.m.wikipedia.org/wiki/The_Heat_Will_Kill_You_First
If you don't like to buy the book just read and watch the numerous articles and videos about this book and its author.
This seems more like a narrative about the climate crisis and heat deaths. Tragic as they are, it doesn't seem like it would answer my question.
If you want to quote a passage from the book that explains whether anything has changed with the OP article in terms of lethality and/or harm of certain levels rH% and °C then I'd be happy to take a look.
I haven't run the numbers, but your assessment seems about right. The lower the humidity, the greater the potential for evaporative cooling, and the higher the max tolerable temperature. No reason to avoid moving to the tropics anytime soon.