It's Monday - Senior's Day for shopping - and I'm off. Usually I walk, but it is
still in the minus teens C so maybe the bus...
From CNN, the debate on feeding oneself given the new US dietary guideline, which
recommends protein but not carbs...
Recommended as per MyPlate:
Dietician recommends:
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and this useful bit of intelligence from my YouTube feed:
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Copilot:
Could humans survive outside an Ice Age. We have evolved to be mammals with an interior temperature higher than exterior temperature comfort...
This is a rich question, and it gets at something people rarely think about: humans evolved inside an Ice Age, but we are not biologically dependent on Ice Age conditions. What we are dependent on is a very narrow band of thermal, ecological, and agricultural stability — and that’s the real constraint.
Let’s unpack it clearly and without drama.
🌡️ 1. Humans are warm‑blooded, but that doesn’t mean we need a cold planet
Our internal temperature (~37°C) is regulated internally. What matters for survival is not the planet’s average temperature, but:
whether we can shed heat efficiently
whether ecosystems remain productive
whether water cycles remain stable
whether food systems can function
Humans can live in climates ranging from Arctic tundra to the Arabian Peninsula. So biologically, we are extremely adaptable.
The Ice Age context didn’t shape us to need cold — it shaped us to be flexible.
🔥 2. The real danger isn’t warmth — it’s heat + humidity beyond human tolerance
There is a hard physiological limit called wet‑bulb temperature.
If the air is too hot and too humid, sweat can’t evaporate, and the body can’t cool itself.
A wet‑bulb of 35°C is unsurvivable for more than a few hours
Even a healthy person in shade with water will die
You essentially “cook” from the inside because heat can’t escape
This is not about comfort — it’s about physics.
In an ice‑free world, large regions of the tropics and subtropics could cross this threshold.
But that’s not because humans “need” an Ice Age.
It’s because the planet’s heat distribution becomes extreme.
🌍 3. Could humans survive on an ice‑free Earth? Yes — but not everywhere
An ice‑free Earth would likely mean:
Sea levels ~60–70 meters higher
Tropical regions too hot for outdoor labor
Massive shifts in rainfall belts
Loss of many current agricultural zones
New habitable zones opening in the far north (Canada, Siberia, Scandinavia)
Humans would survive, but billions would need to move, and civilization would reorganize around new climate belts.
Survival is not the issue.
Stability is.
🧊 4. Humans evolved during an Ice Age because Ice Ages create climate variability
The Quaternary Ice Age (the one we’re in) is characterized by:
fluctuating climates
shifting ecosystems
resource unpredictability
This selected for:
intelligence
cooperation
tool use
mobility
cultural adaptation
But none of these traits require the Ice Age to continue.
They just helped us survive it.
🌱 5. Agriculture is the real bottleneck
Human bodies can tolerate a wide range of climates.
Agriculture cannot.
Crops depend on:
predictable seasons
stable rainfall
moderate heat
fertile soils
An ice‑free Earth would radically reorganize climate zones, and many current breadbaskets (India, U.S. Midwest, China, Brazil) could become marginal or unviable.
Humans would survive — but our current civilization would not look anything like it does today.
🧩 So the clean answer:
**Yes, humans could survive outside an Ice Age.
But our civilization is tuned to the stable climate of the Holocene, not to an ice‑free super‑greenhouse world.**
Biology is flexible.
Agriculture and infrastructure are not.
If you want, we can explore:
What an ice‑free Earth would look like region by region
How Quebec’s climate would shift in a greenhouse world
Whether humans could engineer ways to survive extreme heat
How past greenhouse worlds (like the Cretaceous) actually functioned
Just tell me where you want to take the model next.
Tell me more about wet-bulb temperature: there are places on Earth that do reach 35C... are there other conditions?
Wet‑bulb temperature is one of those concepts that sounds abstract until you realize it’s the actual physiological limit of human survival. And you’re right to question it — because 35 °C wet‑bulb is not the same as 35 °C air temperature. Most places that hit 35 °C air temperature are still far from the lethal zone.
Let’s break it down cleanly.
🌡️ What wet‑bulb temperature actually measures
A wet‑bulb thermometer is wrapped in a damp cloth. As water evaporates, it cools the thermometer.
So wet‑bulb temperature reflects:
heat
humidity
wind
evaporation efficiency
It’s essentially:
“How well can a human body shed heat through sweat?”
If sweat can’t evaporate, the body can’t cool itself.
☠️ The lethal threshold: 35 °C wet‑bulb
This is the hard physical limit.
At 35 °C wet‑bulb, even a healthy person in shade, naked, with unlimited water, will die in a few hours.
Why?
Because at that point, the air is so hot and humid that your sweat cannot evaporate at all.
Your core temperature rises until organs fail.
This is not about comfort.
It’s about thermodynamics.
🔥 Important distinction: 35 °C wet‑bulb ≠ 35 °C air temperature
Most places that reach 35 °C air temperature have wet‑bulb temperatures around 24–28 °C — uncomfortable, but survivable.
To reach 35 °C wet‑bulb, you need something like:
Air temperature: ~40–45 °C
Relative humidity: ~70–90%
Low wind
Direct exposure for hours
This combination is extremely rare today.
🌍 Do any places on Earth reach 35 °C wet‑bulb today?
Very rarely, and only for short periods.
A few locations in the Persian Gulf and Indus River Valley have briefly approached or touched 33–35 °C wet‑bulb for an hour or two.
Examples include:
Jacobabad, Pakistan
Ras al‑Khaimah, UAE
Parts of the Red Sea coast
But these are still borderline events, not sustained lethal conditions.
🧩 Why humidity is the killer
You can survive:
45 °C in a desert (humidity 10%)
35 °C in a humid place (humidity 60%)
But you cannot survive:
35 °C wet‑bulb (e.g., 40 °C with 75% humidity)
Because your body’s only cooling mechanism — evaporation — stops working.
🌬️ Other conditions that matter
Wet‑bulb temperature is influenced by:
1. Wind
Wind increases evaporation, lowering effective wet‑bulb stress.
2. Sun exposure
Direct sunlight adds ~8–10 °C of “radiant heat load” to the body.
3. Clothing
Insulating or non‑breathable clothing reduces evaporative cooling.
4. Acclimatization
People living in hot climates tolerate higher heat loads, but no one can survive above the wet‑bulb limit.
🧠 So the key insight:
**Air temperature alone is not the danger.
Heat + humidity together determine survivability.**
This is why tropical regions are the first to hit physiological limits, not deserts.
If you want, we can go deeper into:
What Quebec’s wet‑bulb limits look like
How wet‑bulb thresholds affect agriculture and labor
How an ice‑free Earth would shift global wet‑bulb zones
Whether humans could engineer ways around the wet‑bulb limit
Just tell me where you want to take it.
So how does one calculate wet-bulb temperature?
Here’s the clean, practical way to think about wet‑bulb temperature: it’s not something you “look up” on a thermometer — it’s something you calculate from ordinary weather data (air temperature + humidity), using a formula that captures how well sweat can evaporate.
Let me give you a clear, usable explanation without drowning you in equations.
🌡️ What you need to calculate wet‑bulb temperature
You only need two inputs:
Air temperature (the usual thermometer reading)
Relative humidity (how saturated the air is)
Everything else (evaporation rate, vapor pressure, etc.) is derived from those.
🧠 A more intuitive way to understand it
Wet‑bulb temperature is basically:
Air temperature minus the cooling effect of evaporation.
If humidity is low → evaporation is strong → wet‑bulb is much lower than air temperature.
If humidity is high → evaporation is weak → wet‑bulb approaches air temperature.
At 100% humidity, wet‑bulb = air temperature (because no evaporation is possible).
🔥 Example: Why 35 °C wet‑bulb is so extreme
Let’s plug in a realistic scenario:
Air temperature: 40 °C
Humidity: 75%
This gives a wet‑bulb of roughly 35 °C — the lethal threshold.
But if humidity drops to 40%, the wet‑bulb falls to ~28 °C, which is uncomfortable but survivable.
This is why deserts can hit 45 °C and still be survivable: humidity is low.
🌍 Why some places get dangerously close
Regions near warm bodies of water (Persian Gulf, Red Sea, Indus Valley) can combine:
extreme heat
extreme humidity
low wind
That’s the deadly trio.
But even there, sustained 35 °C wet‑bulb is still rare today.
🧩 If you want, I can:
walk you through a specific example using real numbers
show how Quebec’s climate compares
explain why wet‑bulb is the true limit of human heat tolerance
map which regions would become uninhabitable in a hotter world
Just tell me where you want to take it next.
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