How Hot Can We Take?

It's the hottest since, it's the wettest since, it's the windiest since .... a lot of records since, eh.

Ok, so the planet is changing (causes are disputed by some, but not those that actually know).

What does that mean for an average human on an average day in average clothes doing average stuff?

Let's start with temperature, I don't really know what my body temperature should be ...

36–37.5°C is a typically reported range for normal body temperature

Well, now I do.

Let's first get cold, what happens to your body as the temperature of it drops?

• 35.5°C – Feeling cold, mild to moderate shivering. This can be a normal body temperature for sleeping.
• 35°C – Threshold for hypothermia. Intense shivering, numbness and bluish/grayness of the skin. There is the possibility of heart irritability.
• 34°C – Severe shivering, loss of movement of fingers, blueness, and confusion. Some behavioral changes may take place.
• 33°C – Moderate to severe confusion, sleepiness, depressed reflexes, progressive loss of shivering, slow heartbeat, shallow breathing. Shivering may stop. The subject may be unresponsive to certain stimuli.
• 32°C – (Medical emergency) – Hallucinations, delirium, complete confusion, extreme sleepiness that is progressively becoming comatose. Shivering is absent. Reflex may be absent or very slight.
• 31°C – Comatose, very rarely conscious. No or slight reflexes. Very shallow breathing and slow heart rate. Possibility of serious heart rhythm problems.
• 28°C – Severe heart rhythm disturbances are likely and breathing may stop at any time. The person may appear to be dead.[citation needed]
• 24–26°C or less – Death usually occurs due to irregular heart beat or respiratory arrest; however, some patients have been known to survive with body temperatures as low as 13.7°C.

Somewhere between 35°C and 34°C it starts to get serious. Don't forget normal body temperature is, at it's lowest, 36°C. One degree drop and we're starting to worry.

Is that the same for heat, as the body gets hotter what happens?

• 38°C – (Classed as hyperthermia if not caused by a fever) – Feeling hot, sweating, feeling thirsty, feeling very uncomfortable.
• 39°C – Severe sweating, and red. Fast heart rate and breathlessness. There may be exhaustion accompanying this. Children and people with epilepsy may suffer convulsions at this temperature.
• 40°C – Fainting, dehydration, weakness, headache, breathlessness, and dizziness may occur as well as profuse sweating.
• 41°C – (Medical emergency) – Fainting, severe headache, dizziness, confusion, hallucinations, delirium, and drowsiness can occur. There may also be palpitations and breathlessness.
• 42°C – Subject may turn red. They may become comatose, be in severe delirium, and convulsions can occur.
• 43°C – Normally death, or there may be serious brain damage, convulsions, and shock. Cardio-respiratory collapse will likely occur.
• 44°C or more – Almost certainly death will occur; however, people have been known to survive up to 46.5°C.

Between 40°C and 41°C it all goes tits up for the body. Again, our normal operating temperature is 37.5°C.

We're a little more adept at coping with heat than cold but still, doesn't take much eh. Aren't we all previous little flowers living in a very small temperature band!

So what's the average temperature out there for you? Look, I'm not gonna do all the work for everyone that could read this so I'll concentrate on those close to me, that's Aotearoa New Zealand, Wales, and Sweden.

• Wellington: 7 - 20°C
• Waitārere Beach: 11 - 22°C 
• Monmouth: 7 - 20°C
• Stockholm: 3 - 24°C

But it's changing and the latest consensus of those that have spent their lives educating, researching, and checking this stuff is that this planets average global temperature is

... expected to increase by 1.5°C by 2050 and 2–4°C by 2100. The WMO predicts that the global mean near-surface temperature will be between 1.1°C and 1.9°C higher than the 1850–1900 baseline between 2024 and 2028.

Add that in:

• Wellington: 11 - 24°C
• Waitārere Beach: 15 - 26°C 
• Monmouth: 11 - 24°C
• Stockholm: 7 - 28°C

[it's at this point the actual scientists amongst you might be thinking, this is all a bit simplistic, happy to hear from you]

Now, I read something about how hot and humid the surrounding environment can be before the body can't cool itself, hang on ... found it:

Scientists [Mike: the "not making it up people"] often use a measure called the wet-bulb temperature to measure heat and humidity together.

It’s the measure of temperature if a thermometer was covered with a wet cloth to evaporate heat and approximates the cooling of skin by sweat. 

“The wet-bulb temperature has to be a few degrees cooler than the inside of your body,” Denning said. Otherwise, heat won’t flow away from your body. 

After an influential study in 2010, climate researchers often use a wet bulb temperature of 35°C [..] at 100% humidity — as an upper limit for human survival and adaptability without cooling.

But ...

A 2022 study in the Journal of Applied Physiology, which used data from heat chamber tests, estimated that the threshold for wet-bulb temperatures is probably closer to 30-31°C [..] for “young, healthy” subjects performing basic life tasks. 

This isn't referring to one hot sunny summer's, it's a bit hot, "Phew wot a scorcher" day, but when that's the base from which the summer days build upon.

So your body struggles to cool down when it's very humid and the temperature is 31°C or more.

What have we learnt?

1. The normal body temperature 
2. What happens as the body cools
3. What happens when the body heats
4. Average temperature of 4 places 
5. Predicted average temperature of the same 4 places in 100 years time
6. What temperature & humidity stops the body cooling itself

I for one will be able to use the reported predictions and updates with a bit more knowledge whilst not just accepting stuff, dismissing stuff, or looking at stuff bemused and confused.

---

Sources:

• Wikipedia: Human body temperature
• NBC News: How hot is too hot for humans?
• NIWA: Overview of New Zealand's climate
• Weather Spark: Climate and Average Weather Year Round in Wellington New Zealand
• Weather2Travel: Monmouth weather by month
• Weather Atlas: Climate and monthly weather forecast Waitarere, New Zealand