Gloomy

 Copilot:

Tell me if this disastrous scenario is plausible, and if not, what saves things for humanity: As a result of consecutive Ice Ages, we loose more and more land to sinking land masses (a bit like Doggerland). Population dwindles, and the capacity to respond deteriorates...

Let’s dig into this with the kind of layered, physical‑realism lens you enjoy. The short version: your scenario is evocative, but the physics of Earth’s climate system and crustal dynamics don’t quite allow it to unfold that way. And the reasons why are actually fascinating — they reveal the built‑in “safety valves” that prevent humanity from being erased by a Doggerland‑style drowning during an Ice Age.

Below is a clean breakdown.

🌍 Is your scenario physically plausible?

❄️ 1. Consecutive Ice Ages don’t cause sinking land — they cause rising land

During an Ice Age, enormous ice sheets accumulate on continents. This produces:

Isostatic depression: the weight of ice pushes land down.

Isostatic rebound: when ice melts, land rebounds upward.

But crucially:

Ice Ages lower sea level, because water is locked in ice.

Interglacials raise sea level, because ice melts.

So the Doggerland analogy is actually the opposite of an Ice Age scenario:

Doggerland drowned after the Ice Age, when sea levels rose ~120 m.

During an Ice Age, Doggerland would have been bigger, not smaller.

➤ Therefore:

Ice Ages do not sink land or drown continents. They expose more land.

🌊 2. Could land sink independently of sea level?

Yes — but not globally, and not in a way that tracks Ice Age cycles.

Land can sink due to:

tectonic subsidence

sediment loading

mantle dynamics

local isostatic effects

But these are:

regional, not global

slow, on the order of mm/year

not synchronized with climate cycles

You cannot get a worldwide “progressive drowning” of continents from these processes.

🌡️ 3. Could multiple Ice Ages in a row collapse human civilization?

Surprisingly, no — at least not in the way you describe.

Humanity has already survived:

dozens of glacial cycles

population bottlenecks

volcanic winters

megadroughts

sea‑level swings of 120 m

And we did this with:

stone tools

no agriculture

no global communication

Modern humanity has:

global food networks

energy storage

migration capacity

scientific forecasting

genetic diversity

technological redundancy

Even a severe glacial period would:

shift populations southward

reduce habitable zones

stress agriculture

…but not cause a civilizational collapse to the point of “no capacity to respond.”

🧭 So what actually “saves” humanity?

Here’s the interesting part: the Earth system itself prevents your scenario from spiraling into extinction.

🛡️ 1. Ice Ages self‑limit

Ice sheets grow until:

albedo increases

CO₂ drops

orbital cycles shift

ice reaches latitudes where summer melting exceeds winter accumulation

This creates a natural cap on glaciation.

🛡️ 2. Sea level cannot rise during an Ice Age

Your scenario requires:

ice growing

sea level rising

land sinking

But physics forces:

ice growing → sea level falling

ice melting → sea level rising

You can’t have both simultaneously.

🛡️ 3. Human adaptability is extreme

Even with:

shrinking coastlines

colder climates

resource stress

humans:

migrate

innovate

reorganize

preserve knowledge

We’ve done it repeatedly.

🔥 Could a modified version of your scenario be plausible?

Yes — if you flip the mechanism.

A more realistic catastrophic scenario would be:

rapid warming, not cooling

ice sheet collapse, not growth

sea level rise, not fall

coastal megacities drowning, not expanding land

This is physically consistent and historically precedented (e.g., Meltwater Pulse 1A).

(meltwater pulses are rapid release of meltwater into the oceans from the collapse of continental ice sheets)

But that’s the opposite of what you proposed.

🧩 If you want your scenario for world‑building or modeling

You can make it plausible by adjusting one variable:

✔️ Instead of Ice Ages, use mantle‑driven subsidence

For example:

A superplume collapses

A craton destabilizes

A megafault causes continental sagging

A methane‑hydrate release triggers runaway warming and sea‑level rise

Then you get:

shrinking land

population collapse

deteriorating response capacity

This would be geophysically coherent.

💬 Want to push this further?

If you want, we can:

build a fully coherent catastrophic‑Earth scenario

map timelines, population impacts, and survival strategies

compare Ice Age vs. warming vs. tectonic collapse

design a scientifically grounded dystopia or alternate history

You tell me the direction, and I’ll help you craft something that feels real.

Fine, repurpose the scenario in terms of coming out of Ice Ages. What part of the Globe keeps going...

Let’s reshape your scenario into something that does fit the physics of deglaciation — and still gives you the dramatic, civilization‑straining pressure you’re aiming for. Coming out of an Ice Age is one of the most chaotic, dangerous, and uneven transitions Earth ever experiences. And it absolutely can create a world where some regions collapse while others keep going.

Below is a grounded, physically coherent version of your scenario.

🌡️ Coming Out of an Ice Age: What Actually Happens

Deglaciation is violent. Not metaphorically — physically.

When an Ice Age ends, the world experiences:

Rapid sea‑level rise (up to 4–5 m per century during meltwater pulses)

Massive coastal flooding

Collapse of ice‑dammed lakes

Mega‑tsunamis from ice shelf failures

Chaotic climate swings (Younger Dryas–style cold snaps)...https://lessthan3ley.wordpress.com/2014/06/27/lake-agassiz/

Isostatic rebound that warps coastlines and river systems

Shifts in monsoons and storm tracks

This is the period when Doggerland drowned, when the Black Sea flooded, when North America’s drainage reorganized, and when human populations were forced into radical migrations.

So your scenario becomes:

Not sinking land, but rising seas + unstable land

Not dwindling land from cold, but dwindling land from meltwater

Not population collapse from glaciation, but collapse from deglaciation chaos

This is physically consistent and historically precedented.

🌍 Which parts of the world “keep going”?

During deglaciation, survival depends on three factors:

1. Distance from melting ice sheets

Regions far from the Laurentide, Fennoscandian, and Patagonian ice sheets avoid:

isostatic warping

glacial outburst floods

mega‑tsunamis

catastrophic river reorganization

2. Elevation above rapidly rising seas

Low‑lying coasts drown first:

Northern Europe

Eastern North America

Southeast Asia’s continental shelves

The Persian Gulf basin

Highlands and plateaus become refuges.

3. Climate stability during the transition

Some regions experience wild swings in rainfall and temperature; others remain relatively stable.

🧭 Regions that remain functional or even thrive

These are the places that “keep going” in your scenario — the ones that maintain continuity, population, and adaptive capacity.

🟤 1. The African Highlands

Ethiopia

Kenya

Tanzania

Rwanda/Burundi

South African plateau

Why they survive:

Far from ice sheets

High elevation

Stable rainfall patterns

No catastrophic sea‑level impacts

Historically, these regions were refugia during past climate swings.

🟤 2. The Tibetan Plateau and Himalayan foothills

Nepal

Bhutan

Northern India

Western China

Why they survive:

High elevation

Large freshwater sources

Distance from marine flooding

They face monsoon shifts, but not drowning.

🟤 3. The Andes

Peru

Bolivia

Ecuador

Northern Chile/Argentina

Why they survive:

High elevation

Stable climate zones

Distance from northern ice sheets

The Andes have been human refuges for 12,000+ years.

🟤 4. Australia’s interior highlands

Great Dividing Range

Tasmanian highlands

Why they survive:

No glaciation

Minimal sea‑level impact

Stable continental interior

Australia becomes a climate refuge in many deglaciation models.

🟤 5. Central Asia

Kazakhstan uplands

Mongolia

Altai region

Why they survive:

High elevation

Continental climate stability

No major flooding

These regions were migration corridors during past deglaciations.

🌊 Regions that collapse or lose continuity

These are the places that don’t keep going — the ones that lose land, infrastructure, and population.

🔵 1. Northern Europe

UK

Scandinavia

Baltic region

Why they collapse:

Isostatic rebound warps coastlines

Sea‑level rise floods lowlands

Meltwater pulses drown Doggerland‑like regions

🔵 2. Eastern North America

St. Lawrence basin

Hudson Bay rim

U.S. East Coast

Why they collapse:

Laurentide meltwater floods

River systems reorganize

Sea‑level rise swamps coastal plains

🔵 3. Southeast Asia

Sundaland (Indonesia, Malaysia, Vietnam)

Mekong and Irrawaddy deltas

Why they collapse:

120 m sea‑level rise drowns continental shelves

Monsoon chaos

Loss of arable land

🔵 4. Middle East coastal basins

Persian Gulf

Red Sea coasts

Why they collapse:

Rapid flooding

Saltwater intrusion

Extreme heat during interglacial peaks

🧩 What this gives you for your scenario

You now have a world where:

Land is disappearing, but because of meltwater, not sinking

Civilizations near coasts collapse

Highland refuges become the new centers of continuity

Population dwindles, not from cold, but from displacement and resource chaos

Response capacity deteriorates because infrastructure is coastal and gets drowned

Humanity survives, but in fragmented, inland, elevated pockets

This is a scientifically coherent, dramatic, and narratively rich scenario.

If you want, we can map:

migration routes

which cultures survive

how technology regresses or adapts

how geopolitics reorganizes around highland refuges

Just tell me the direction you want to take it

I have read that - at one point - the entirety of human population was down to some 20,000 individuals. What caused that?

You’re touching one of the most intriguing and hotly debated chapters of human evolutionary history: the population bottlenecks. And yes — several studies have suggested that at certain points, the global population of our ancestors may have dropped to something on the order of 20,000 individuals, or even fewer.

But the cause depends on which bottleneck we’re talking about, because there are two major candidates in the scientific literature.

Below is a clean, evidence‑based breakdown grounded in the search results.

🌋 1. The Toba Super‑Eruption Hypothesis (~74,000 years ago)

This is the most famous explanation for a near‑extinction event.

Some researchers propose that the Toba supervolcano in Indonesia erupted catastrophically, triggering:

volcanic winter

global cooling

collapse of ecosystems

famine and migration bottlenecks

This theory suggests the human population may have dropped to a few thousand individuals globally.

However:

Genetic evidence is mixed.

Some populations (e.g., in Africa) show continuity through this period.

Many scientists now think Toba was disruptive but not globally apocalyptic.

So Toba remains possible, but not universally accepted.

🧊 2. The Deep Ancestral Bottleneck (~930,000 years ago)

A much more recent study (2023) proposed a far older and more severe bottleneck:

Occurring around 930,000 years ago

Lasting ~100,000 years

Reducing the ancestral human population to ~1,280 breeding individuals

This claim comes from a genomic modeling paper suggesting that almost 99% of human ancestors may have been wiped out during this period.

Possible causes include:

severe climate cooling

prolonged drought

habitat fragmentation

loss of food sources

This is still controversial — the method is new, and not all paleoanthropologists agree with the interpretation.

🌍 3. Multiple Smaller Bottlenecks Throughout Human History

Genetic studies show that many human groups have experienced bottlenecks at different times due to:

climate swings

migrations

founder effects

isolation

local catastrophes

These events reduce genetic diversity but don’t necessarily imply global near‑extinction. This pattern is well‑documented across many populations.

🧬 So where does the “20,000 individuals” number come from?

That figure is a general estimate of the effective population size of early Homo sapiens during parts of the Late Pleistocene.

It reflects:

limited genetic diversity

small breeding populations

scattered, isolated groups

It does not necessarily mean only 20,000 humans were alive — just that the breeding population was roughly that size.

🧭 The most likely cause?

Based on current evidence:

Not one single catastrophe, but

a combination of climate instability, habitat fragmentation, and small, dispersed populations

The Toba eruption may have intensified an already small population, but the deeper bottleneck around 930,000 years ago — if confirmed — would have been driven by long-term climate stress, not a single event.

If you want, we can dig into:

how these bottlenecks shaped human evolution

why genetic diversity is so low compared to other species

how small populations survived and expanded

what this means for your Ice Age/deglaciation scenario

Just tell me where you want to take it.

I was just trying to find what combination of events might extinguish or cripple humanity irrevocably (tied to climate events)...

You’re asking the right kind of question — not “what kills us instantly,” but what combination of climate‑driven stresses could push humanity past the point of recovery. And the truth is: single events almost never do it. It’s compound stressors that break complex systems.

What follows is a grounded, physically realistic map of the only climate‑linked combinations that could plausibly cripple humanity beyond recovery — and the built‑in limits that usually prevent total extinction.

🌡️ 1. Runaway Warming + Hydrological Collapse

This is the closest thing Earth can produce to a global, civilization‑ending cascade.

🔥 Trigger

Rapid warming (5–8°C globally)

Collapse of monsoons

Persistent megadroughts across food‑producing regions

🧨 Consequences

Agricultural belts fail simultaneously

Freshwater systems collapse

Wet‑bulb temperatures exceed survivability in tropical regions

Mass migration overwhelms remaining stable zones

🧩 Why this could cripple humanity

Humans can’t survive >35°C wet‑bulb conditions for long. If these zones expand across South Asia, the Middle East, and parts of Africa, billions lose habitability.

🛡️ Why it doesn’t fully extinguish us

High‑latitude refuges (Canada, Scandinavia, Patagonia, New Zealand) remain viable

Mountain regions stay habitable

Humans adapt technologically

This scenario collapses civilization but leaves pockets of survivors.

🌊 2. Deglaciation Chaos + Sea‑Level Shock

This is the scenario you were circling earlier — and it’s more dangerous than the Ice Age itself.

🌊 Trigger

Rapid melting of Greenland and West Antarctica

Meltwater pulses raising sea level 3–5 m per century

Collapse of coastal megacities

🧨 Consequences

2–3 billion people displaced

Loss of ports, farmland, and infrastructure

Salinization of river deltas (where most food is grown)

Economic collapse from the destruction of coastal hubs

🧩 Why this could cripple humanity

Civilization is coastal. Lose the coasts, lose the system.

🛡️ Why it doesn’t extinguish us

Inland highlands remain stable

Agriculture relocates

Humans migrate

This is a civilization reset, not extinction.

🌋 3. Supervolcano + Glacial State Shift

This is the closest natural analogue to a “global kill switch.”

🌋 Trigger

Yellowstone‑scale eruption

Volcanic winter lasting 5–10 years

Collapse of global agriculture

Followed by abrupt warming as aerosols clear

🧨 Consequences

Famine on a global scale

Breakdown of supply chains

Mass die‑off

🧩 Why this could cripple humanity

A multi‑year agricultural shutdown is the single most dangerous event for a globalized species.

🛡️ Why it doesn’t extinguish us

Equatorial regions retain some growing seasons

Marine food chains recover

Humans survive in pockets

This is a severe bottleneck, not extinction.

🧊 4. Abrupt Ice Age Onset + Resource Collapse

This is the inverse of the warming scenario.

❄️ Trigger

Shutdown of the Atlantic Meridional Overturning Circulation (AMOC)

Rapid cooling in Europe and North America

Expansion of ice sheets over centuries

🧨 Consequences

Loss of arable land in the Northern Hemisphere

Mass migration southward

Conflict over shrinking habitable zones

🧩 Why this could cripple humanity

Food production collapses in the world’s breadbaskets.

🛡️ Why it doesn’t extinguish us

Tropics remain habitable

Southern Hemisphere is barely affected

Humans adapt

This is a geopolitical catastrophe, not a species‑ending one.

🌍 5. The Only Truly Existential Climate Combination

If you want a scenario that could push humanity into irreversible collapse, it requires three simultaneous failures:

🧨 (1) Global food system collapse

Triggered by:

megadroughts

monsoon failure

volcanic winter

sea‑level loss of deltas

🧨 (2) Loss of refugia

If both:

high‑latitude regions become unstable

AND mountain refuges lose water sources

…then humanity loses its fallback zones.

🧨 (3) Breakdown of knowledge continuity

If:

population drops below a few hundred thousand

AND survivors are scattered

AND technological infrastructure collapses

…then recovery becomes extremely slow or impossible.

This combination is rare but not impossible.

🧭 The Deep Truth

Humanity is extremely hard to extinguish.

Civilization is extremely easy to cripple.

The Earth system almost always leaves:

highlands

high latitudes

inland plateaus

microclimates

freshwater refuges

Even in the worst climate catastrophes, these zones persist.

So the real danger isn’t extinction — it’s fragmentation, loss of complexity, and irreversible civilizational regression.

If you want, we can build:

a fully coherent near‑extinction scenario

a map of surviving refuges

a timeline of collapse

a model of how many humans remain and where

Just tell me which direction you want to explore.