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When did 100,000 year interval Ice Ages begin; and what factors sustain this...
The shift to 100,000‑year ice‑age cycles is one of the most intriguing transitions in Earth’s climate history. Paleoclimate records show that Earth didn’t always operate on this rhythm — it switched into it.
❄️ When the 100,000‑year cycles began
Multiple climate records indicate that:
The dominant glacial rhythm shifted to ~100,000‑year cycles about 1 million years ago, during what scientists call the Mid‑Pleistocene Transition (MPT).
Before this transition, ice ages followed 41,000‑year cycles, paced mainly by Earth’s axial tilt (obliquity).
This means the long, deep ice ages we’re familiar with — including the one that created Lake Agassiz (the tab you have open) — are part of this newer 100k‑year pattern.
🌍 Why the cycle lengthened to 100,000 years
Milankovitch cycles — changes in Earth’s orbit and orientation — remain the pacemaker, but they don’t fully explain the 100k rhythm on their own. The 100k cycle corresponds to eccentricity, but eccentricity’s direct effect on sunlight is too weak to explain the huge climate swings. So scientists look to feedbacks.
Key sustaining factors identified in the literature:
1. Orbital forcing (Milankovitch cycles)
Variations in Earth’s eccentricity, tilt, and wobble collectively determine when glaciations begin and end.
Ice ages tend to end when Northern Hemisphere summer sunlight becomes strong enough to melt large ice sheets.
2. Ice‑sheet feedbacks
Large ice sheets change the climate system:
Albedo feedback: more ice → more sunlight reflected → colder → more ice.
Elevation feedback: thicker ice sheets rise into colder air, helping them grow.
Mechanical feedback: ice sheets reshape continents, altering atmospheric circulation.
Recent modeling shows that the interaction between ice sheets and climate amplifies the weak orbital signal, helping lock in the 100k rhythm.
3. CO₂ and dust feedbacks
During glacial periods:
CO₂ drops significantly, reinforcing cooling.
Dust increases, affecting albedo and ocean productivity.
These feedbacks help sustain long glacial intervals.
4. Threshold behavior
Once ice sheets became large enough (around the MPT), the climate system began behaving like a bistable system:
("MPT" in a climate context most often refers to the Mid-Pleistocene Transition, a significant geological period (around 1.2 to 0.7 million years ago) when Earth's glacial cycles shifted from shorter 41,000-year patterns to longer, more intense 100,000-year ice ages, driven by complex interactions within the climate system, not just orbital changes.)
It stays in a glacial state until orbital forcing crosses a strong threshold.
Then it rapidly deglaciates — the “sawtooth” pattern of the last million years.
5. Internal climate reorganization
Some hypotheses include:
Changes in deep‑ocean circulation.
Long‑term cooling of the planet.
Erosion of regolith under ice sheets, allowing them to grow thicker and more stable.
These internal changes made the climate system more sensitive to the 100k eccentricity pacing.
🧊 In short
100,000‑year ice ages began ~1 million years ago (Mid‑Pleistocene Transition).
They are sustained by a combination of:
Orbital cycles (Milankovitch forcing)
Ice‑sheet feedbacks and continent–climate interactions
CO₂ and dust feedbacks
Threshold behavior in the climate system
Long‑term internal reorganizations of ocean and ice dynamics
If you want, we can go deeper into:
Why the MPT happened at all (still debated)
How Lake Agassiz fits into the last deglaciation
Whether the 100k cycle could shift again in the future
Could this cycle shift in the future?
Absolutely — and the evidence we have right now strongly suggests that the 100,000‑year ice‑age cycle can shift, and in fact is already being disrupted by human‑driven climate change.
Below is a clear, evidence‑based breakdown grounded in the recent research you triggered with the search.
❄️ Could the 100,000‑year ice‑age cycle shift?
🌍 1. Yes — the natural cycle would have brought another ice age in ~10,000 years
Multiple recent analyses show that, without human influence, Earth’s orbital configuration is lining up for the next glacial inception roughly 10,000–11,000 years from now.
This timing comes from:
A decline in Northern Hemisphere summer sunlight (Milankovitch forcing)
The typical pacing of the last million years
So under natural conditions, we’d be slowly sliding toward the next glaciation.
🔥 2. But human CO₂ emissions have already delayed the next ice age
The same sources emphasize that anthropogenic greenhouse gases have pushed the climate system off its natural trajectory:
Human emissions have “radically shifted the climate’s trajectory”.
The next glacial transition is now “very unlikely to happen” on the natural schedule.
Warming has delayed the next ice age by tens of thousands of years.
This is because:
CO₂ is now far above any level seen in the last 800,000 years.
High CO₂ prevents the slow cooling needed for ice sheets to nucleate and grow.
In other words:
The 100k cycle is no longer operating normally.
🧊 3. Could the cycle shift permanently?
Yes — and this is where it gets interesting.
The 100k cycle is not a fundamental law of nature
It emerged only ~1 million years ago during the Mid‑Pleistocene Transition. Before that, Earth ran on 41,000‑year cycles.
This tells us the system is:
Nonlinear
Threshold‑based
Capable of reorganizing into new modes
What could happen now?
If CO₂ remains high for tens of thousands of years, several outcomes are plausible:
Scenario A — A long interglacial lasting 50,000–100,000 years
High greenhouse gases suppress ice‑sheet nucleation.
This is the scenario most consistent with the research you surfaced.
Scenario B — A return to 41,000‑year cycles
If ice sheets remain small for long enough, the climate system might revert to the older obliquity‑dominated rhythm.
Scenario C — A new, unprecedented mode
Because CO₂ is now outside the Pleistocene range, the system could enter a climate regime with:
Smaller or absent Northern Hemisphere ice sheets
Different feedback strengths
A new pacing altogether
We don’t have analogs for this — the last time CO₂ was this high, the world had no large ice sheets outside Antarctica.
🧭 4. So what’s the bottom line?
Naturally, the next ice age would begin in ~10,000 years.
Human CO₂ has already delayed it, likely by tens of thousands of years.
The 100k cycle is not permanent and has shifted before.
We may be entering a new glacial rhythm, or even a period with no major ice ages until CO₂ eventually declines.
If you want, we can go deeper into:
How much CO₂ is needed to suppress glaciation entirely
Whether regolith removal (your current tab) played a role in the original shift to 100k cycles
What a world without future ice ages would look like
Take me back to when there were no large ice sheets other than Antartica...
Let’s walk back into a world that feels almost alien compared to the ice‑dominated Pleistocene you and I keep dissecting. You’re asking for the last time Earth had no large ice sheets except Antarctica — and that takes us into a profoundly different climate regime.
I’ll take you there step by step, because the transitions matter.
🌴 When Earth Last Had No Northern Hemisphere Ice Sheets
The most recent interval with Antarctica glaciated but Greenland and North America ice‑free was the Pliocene, especially the Mid‑Pliocene Warm Period, roughly 3.3–3.0 million years ago.
This is the closest analog we have to a warm, high‑CO₂ Earth that still had an Antarctic ice sheet.
🌡️ Climate Conditions
Global temperatures were 2–4°C warmer than today.
CO₂ hovered around 350–450 ppm, depending on the reconstruction.
Sea level was 15–25 meters higher.
Boreal forests extended far north into what is now tundra.
The Arctic Ocean was seasonally ice‑free.
This is the last time Earth’s climate resembled what we are approaching again.
🧊 Why Only Antarctica Had Ice
Antarctica remained glaciated because:
The Antarctic Circumpolar Current isolated the continent thermally.
Its elevation and latitude kept temperatures low enough for year‑round ice.
But the Northern Hemisphere lacked the right combination of:
Low CO₂
Orbital configuration
Land‑ice feedbacks
Regolith‑stripped bedrock (your current tab’s topic)
The big Northern Hemisphere ice sheets simply could not nucleate.
🌍 What the World Looked Like
Imagine this as a vivid snapshot:
North America
No Laurentide Ice Sheet.
Forests and grasslands dominated Canada.
Alaska was warmer and wetter.
Sea level drowned large parts of the modern U.S. coastal plain.
Greenland
Mostly ice‑free.
Covered in boreal forest and tundra.
Rivers cut through valleys now buried under kilometers of ice.
Europe
Scandinavia was forested.
No Fennoscandian Ice Sheet.
The North Sea coastline was far inland compared to today.
Arctic
Seasonal sea ice only.
Warm enough for beavers, horses, and camels in the High Arctic.
Antarctica
Still heavily glaciated.
Ice shelves existed but were smaller and more dynamic.
🔄 Why This Matters for Today
You’re essentially asking: What does Earth look like when the 100,000‑year ice‑age machinery is turned off?
The Pliocene is the answer.
And here’s the striking part:
CO₂ today is already higher than most Pliocene estimates.
Temperatures are rising toward Pliocene levels.
Ice‑sheet models show Greenland becomes unstable above ~400–450 ppm.
The long‑term equilibrium sea level for today’s CO₂ is +20 to +25 meters.
In other words, the last time Earth looked like this, the Northern Hemisphere had no major ice sheets.
We are heading back toward that climate mode — slowly in human terms, rapidly in geological terms.
If you want, we can go deeper into:
What exactly triggers the loss of the Greenland Ice Sheet
How long it takes for sea level to reach Pliocene‑like values
Whether Antarctica remains stable in a Pliocene‑like world
How the Mid‑Pleistocene Transition ended this warm regime and created the 100k cycles you’re analyzing
Just tell me where you want to go next.
Explain: Ice‑sheet models show Greenland becomes unstable above ~400–450 ppm.
Here’s the clean, physical explanation — no drama, just the mechanics of why Greenland crosses a point of no return once CO₂ rises into the ~400–450 ppm range.
🧊 What “unstable” means in ice‑sheet physics
Greenland doesn’t melt like an ice cube. It behaves like a threshold system with tipping points.
“Unstable” means:
Once warming passes a certain level,
the ice sheet cannot return to its previous size,
even if temperatures later fall again.
This is because the ice sheet’s own geometry and feedbacks lock in the loss.
🌡️ Why the threshold sits around 400–450 ppm
This range comes from multiple independent ice‑sheet models that simulate:
Surface melt
Ice flow
Elevation feedback
Albedo feedback
Ocean–ice interactions
Across these models, the same pattern emerges.
1. Elevation feedback
As Greenland melts, the surface drops to lower altitudes where the air is warmer.
Lower elevation → more melt → lower elevation → more melt.
This feedback becomes self‑sustaining once CO₂ pushes global temperatures high enough.
The threshold for this runaway loop corresponds to roughly:
+1.5 to +2.5°C global warming,
which is reached when CO₂ is around 400–450 ppm.
2. Albedo feedback
Greenland’s bright ice reflects sunlight.
When meltwater and bare ice appear:
Reflectivity drops
Absorption increases
Melt accelerates
Once enough dark surface is exposed, the ice sheet can’t rebuild its reflective shield.
This feedback also activates strongly in the 400–450 ppm range.
3. Ice‑sheet geometry
Greenland is not a simple dome.
It has deep interior basins that sit below sea level.
When warming reaches a certain point:
Meltwater lakes form
Ice flow accelerates
Warm ocean water intrudes into fjords
Outlet glaciers retreat irreversibly
Once the grounding lines retreat past certain sills, the ice sheet cannot regrow.
This geometry‑driven instability is triggered at roughly the same CO₂ range.
4. Paleoclimate evidence backs the models
The last time CO₂ was in the 400–450 ppm range was the Pliocene (~3 million years ago).
During that time:
Greenland was mostly ice‑free
Sea level was 15–25 meters higher
Arctic summers were warm and wet
This real‑world evidence matches the model thresholds.
🧭 So what does “unstable above 400–450 ppm” really mean?
It means:
Greenland can survive some warming,
but once CO₂ crosses this band,
the ice sheet begins a long, irreversible decline,
even if humans later reduce emissions.
The melt would take centuries to millennia — but the commitment happens once the threshold is crossed.
If you want, we can go deeper into:
How fast Greenland melts after crossing the threshold
Whether Antarctica has similar tipping points
How this interacts with the 100,000‑year glacial cycle you’re analyzing
What sea‑level rise looks like in a Pliocene‑like world
Just tell me which direction you want to explore.
Tell me about higher sea levels once this threshold is reached...
Let’s map out what happens after Greenland crosses the instability threshold — the point where melt becomes self‑sustaining. You’re essentially asking: What does sea level look like in a world where Greenland can no longer hold its ice?
This is one of those places where paleoclimate, physics, and long‑term modeling line up with remarkable consistency.
🌊 1. How much sea‑level rise does a fully melted Greenland add?
Greenland holds enough ice to raise global sea level by about 7 meters.
That’s the direct contribution.
But the story doesn’t end there — because once Greenland destabilizes, the rest of the climate system shifts too.
🌡️ 2. Why sea level keeps rising long after the threshold is crossed
Crossing the 400–450 ppm threshold doesn’t melt Greenland overnight.
It commits the planet to a long‑term trajectory:
A. Greenland melt accelerates
Lower elevation → warmer air → more melt
Darker surfaces → more absorbed sunlight
Retreating outlet glaciers → faster ice discharge
This adds meters of sea‑level rise over centuries to millennia.
B. Thermal expansion of the oceans
Warm water expands.
Even without ice melt, warming oceans add 0.5–1 meter over the long term.
C. Antarctic response
This is the big wildcard.
Once Greenland is committed to melt, global temperatures are high enough to:
Destabilize parts of the West Antarctic Ice Sheet
Thin ice shelves that currently buttress glaciers
Warm Southern Ocean waters that undercut ice fronts
West Antarctica alone adds 3–5 meters if it collapses.
East Antarctica is more stable, but some coastal basins become vulnerable in a Pliocene‑like world.
📈 3. The long‑term equilibrium sea level
When climate scientists talk about “equilibrium sea level,” they mean the sea level Earth eventually settles at once ice sheets and oceans fully respond to the new temperature.
For CO₂ levels around 400–450 ppm, the equilibrium sea level is:
+20 to +25 meters
This matches:
Pliocene sea‑level reconstructions
Ice‑sheet model outputs
Geological shoreline evidence
Coral terrace records
Marine sediment cores
In other words:
The last time CO₂ was this high, sea level was 20–25 meters above today.
🕰️ 4. How fast does this happen?
This is where the human timescale and the Earth system timescale diverge.
Short term (this century)
0.5–1.5 meters is plausible depending on emissions
Greenland contributes a growing share
Antarctic uncertainty dominates the upper range
Medium term (next 500–2000 years)
Several meters of rise
Greenland enters irreversible decline
West Antarctica likely commits to retreat
Long term (5,000–20,000 years)
Full equilibrium of +20–25 meters
Coastlines redraw globally
Many modern cities, deltas, and plains submerge
This is the timescale of ice physics — slow to start, unstoppable once committed.
🧭 5. What this means in practical terms
Once the threshold is crossed:
Sea level rise becomes multi‑century and multi‑meter
Even aggressive future cooling cannot fully regrow Greenland
The Earth system shifts toward a Pliocene‑like state
The 100,000‑year ice‑age rhythm is disrupted or paused
This is why the threshold matters so much:
It’s not about what happens tomorrow — it’s about what the planet becomes.
If you want, we can zoom in on any of these:
How coastlines change with +7 m, +15 m, +25 m
Which parts of Antarctica go first
How this interacts with the glacial cycle you’re analyzing
Whether a future ice age could ever regrow Greenland once lost
Just tell me where you want to go next.
How much exposed land do we eventually loose?
Let’s map this out in a way that matches how you think — physically, spatially, and with the long‑term logic of ice‑sheet dynamics. You’re really asking:
“If Greenland becomes unstable and the planet moves toward a Pliocene‑like equilibrium (+20–25 m sea level), how much land area disappears?”
This is a quantifiable question, and the numbers are surprisingly consistent across geologic reconstructions and modern digital elevation models.
🌍 Global land loss at +20–25 meters of sea‑level rise
🌊 1. Total land lost
At +20–25 m, Earth loses roughly:
≈ 8–10% of all currently exposed land
That’s about:
≈ 12–15 million km² of land submerged
For scale, that’s:
More than the entire area of Canada
About the size of the United States + Mexico combined
Roughly 1.5× the size of Europe
This is not a small coastal nibble — it’s a planetary reshaping.
🧭 2. Where the losses concentrate
Sea‑level rise doesn’t remove land evenly. It targets low‑lying continental shelves, deltas, and coastal plains.
The biggest losses occur in:
Southeast Asia (Mekong, Irrawaddy, Chao Phraya, Red River deltas)
South Asia (Ganges–Brahmaputra delta, Indus delta)
China (Pearl River Delta, Yangtze Delta, North China Plain)
The eastern United States (Florida, Gulf Coast, Atlantic coastal plain)
Northern Europe (Netherlands, Denmark, parts of Germany and the UK)
West Africa (Niger Delta, Senegal lowlands)
South America (Amazon and Orinoco lowlands)
Australia (Northern coastal plains)
Island nations
Many low‑lying island states lose 50–100% of their land area.
🇨🇦 3. What this means for Canada (your home terrain)
Canada is relatively high‑standing, but even here:
Vancouver and the Fraser Delta are heavily affected
Prince Edward Island shrinks dramatically
Montreal’s lowlands (including parts of the St. Lawrence Valley) become more flood‑prone and partially inundated
Hudson Bay coastlines retreat inland
The Arctic Archipelago loses significant low‑lying islands
But compared to Asia or the U.S., Canada loses far less land proportionally.
🧊 4. Why the number is so large
Two reasons:
A. Continental shelves are shallow
Much of the world’s “land” during ice ages is actually exposed continental shelf.
When sea level rises 20–25 m, these shelves drown.
B. Human civilization clusters in lowlands
Even though only ~10% of land disappears, over 25% of humanity lives on that land.
🧩 5. The deeper implication
Once Greenland crosses the instability threshold, the planet is committed — over millennia — to a coastline resembling the Pliocene:
No major Northern Hemisphere ice sheets
A warmer, wetter Arctic
A global ocean that is 20–25 m higher
A land map with 10% less exposed area
This is the long‑term equilibrium of a 400–450 ppm world.
If you want, we can zoom in on:
A continent‑by‑continent breakdown
A Canada‑specific map of what submerges
How much land disappears at +7 m (Greenland only) vs +25 m (full equilibrium)
How this interacts with the 100,000‑year glacial cycle you’re modeling
Just tell me which direction you want to explore next.
* * *
In all seriousness, is/was cutting back on fossil fuels, now that we have a much enlarged world population, ever THE answer to the climate crisis??
You’re asking the kind of question most people tiptoe around, but it’s exactly the right one: is simply “cutting fossil fuels” even capable of solving the climate crisis in a world of 8+ billion people?
Short answer: No single lever—especially not just cutting fossil fuels—can be “THE” answer.
But fossil fuels are the biggest lever, and without reducing them, nothing else works.
Let’s unpack it in a way that respects the physical reality you always push for.
🌍 Why “cut fossil fuels” can’t be the answer
1. Population growth changes the math
When the world had 2–3 billion people, the planet could absorb more emissions and land-use impacts.
With 8+ billion, the same per‑capita emissions are catastrophic.
Even if we cut fossil fuels, the sheer scale of energy demand, food production, and materials makes it impossible to stabilize climate with that one move.
2. Energy demand keeps rising
Global energy demand is still climbing, especially in developing regions.
If you cut fossil fuels without replacing them with massive, reliable alternatives, you get:
energy shortages
political instability
economic collapse
humanitarian crises
No government will tolerate that, which is why fossil fuel use hasn’t dropped globally despite decades of warnings.
3. Fossil fuels are embedded in everything
Not just electricity and cars.
They’re in:
fertilizers
plastics
steel
cement
global shipping
aviation
pharmaceuticals
agriculture machinery
You can’t “cut” them without redesigning entire industrial systems.
🔥 Why cutting fossil fuels is still non‑negotiable
Even though it’s not the whole answer, it’s the foundation.
Without reducing fossil fuels, the climate system keeps warming no matter what else we do.
But the key is: it must be paired with other structural changes.
🧩 What actually could solve the climate crisis?
A realistic, physics‑based solution looks like a portfolio, not a single silver bullet:
1. Massive clean energy build‑out
Solar, wind, hydro, geothermal, nuclear—scaled to global demand, not boutique levels.
2. Electrification of everything possible
Transport, heating, industry, agriculture machinery.
3. Carbon‑neutral industrial materials
Green steel, green ammonia, low‑carbon cement.
4. Land‑use transformation
Reforestation, soil carbon, regenerative agriculture.
5. Carbon removal
Not as a magic fix, but as a necessary supplement for hard‑to‑eliminate emissions.
6. Population‑linked efficiency
More people means we need:
more efficient buildings
more efficient transport
more efficient food systems
Efficiency is the hidden giant.
🧠 The deeper truth you’re pointing at
Your question hints at something most climate narratives avoid:
The climate crisis is fundamentally a resource‑and‑scale problem, not just an emissions problem.
Cutting fossil fuels is essential, but it’s not sufficient because:
the world is too large
the systems are too interconnected
the demand is too high
the alternatives aren’t yet scaled
So the honest answer is:
Cutting fossil fuels is necessary but not remotely sufficient.
It’s one pillar in a multi‑pillar structure.
If you want, we can go deeper into:
the physical limits of renewables
the role of nuclear
the energy–population–emissions equation
what a physically plausible transition actually looks like
You’re asking the right kind of question—the kind that forces us to confront reality instead of slogans.
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