It's the Ocean not the Atmosphere, dummy!

[Anomalism]

That was my point.

On that narrow point, yes; you’re right. Both AMOC changes and orbital/insolation changes ultimately influence Arctic ice through the same end pathway.

The disagreement isn’t that connection, it’s what sets the timing and direction of those changes over long timescales.

 

[ding]

Ocean currents absolutely existed throughout geologic timescales.

The point is that having a persistent internal mechanism does not automatically mean it is the primary pacemaker of glacial cycles.

The disagreement isn’t “do ocean currents matter?” It’s “do they alone generate the long-term, orbitally structured pacing of ice age cycles, or are they responding to that pacing while amplifying it?”

I don't see "clockwork" pacemaking here. I see a loose pattern.

 

[ding]

“Responds” means Antarctica’s temperature, ice, and surrounding ocean conditions shift in step with orbital changes, but without driving global ice age timing. It follows orbital cycles mainly through changes in seasonal sunlight and ocean heat, especially the 41,000 year tilt cycle.

The northern hemisphere behaves differently because it has large continental ice sheets that can grow and collapse dramatically. That amplifies climate changes and produces the dominant 100,000 year glacial cycles, while Antarctica’s more stable, ocean isolated ice sheet mostly mirrors the orbital forcing rather than pacing it.

Wouldn't that response be out of step with the northern hemisphere's response? Is that seen?

 

[ding]

D-O events show that ocean circulation can flip climate state quickly, but they don’t match the global ice age pacing. They are mainly North Atlantic/Northern Hemisphere features riding on top of a larger glacial background, not the mechanism that sets when full glacial–interglacial transitions start and end.

The 41k vs 100k shift isn’t explained by hemispheres having different cycles. It reflects a change in how the whole Earth system responds to orbital forcing. Antarctica still follows the 41k obliquity signal, but it doesn’t generate the global ice volume swings that define the 100k cycle because it lacks large, variable land ice.

The NH dominates the equation. How the NH goes, so goes the world. I don't think anyone knows what the pacing is for changing currents. But what we do know is that the ocean can abruptly trigger glaciation and deglaciation in the NH so it can't be ruled out as the source.

 

[ding]

But they are not the same mechanism. AMOC is an internal heat redistribution process, while ice sheet change affects the planet’s overall energy balance over long timescales. The key question is what sets the slow pacing of those transitions over tens of thousands of years.

You keep saying they are not the same mechanism like that means something. Once glaciation is triggered in the NH regardless of the mechanism, the feedbacks are the same.

 

[ding]

On that narrow point, yes; you’re right. Both AMOC changes and orbital/insolation changes ultimately influence Arctic ice through the same end pathway.

The disagreement isn’t that connection, it’s what sets the timing and direction of those changes over long timescales.

Yes, and where you see orbital clockwork, I see something less than clockwork.

 

[EMH]

Once glaciation is triggered in the NH regardless of the mechanism

so what "triggers glaciation" in NH?

 

[Moonglow]

It's the Ocean not the Atmosphere, dummy!​

It would be if there were no gravity.

 

[Mushroom]

I don't see "clockwork" pacemaking here. I see a loose pattern.

View attachment 1254233

As somebody that has studied geology for decades, I see the pattern clearly. And it is related to this.



It is hard to see in almost any plate tectonics animation, but the cause of our current climactic conditions can be seen in the animation above at roughly 1 minute. Where once was a large gap between North and South America which allowed water to traverse freely between the Atlantic and Pacific allowed our planet to remain warm. Then around 10 mya that started getting restricted, forcing the global currents to shift and at the same time become colder because they were spending more time near the poles.

That restriction corresponds to Antarctica freezing over around 14 mya, and it being completely slammed shut with the rise of Panama corresponds with the complete severing of that current and the start of the current Ice Age.

I have long compared our current conditions to a sick individual going through cycles of fever and chills. The planet wants to be warmer, it was significantly warmer throughout most of the history of our planet. But the isolation of the oceans is locking the things that drive the warmer temperatures into much more constrained basins and forcing temperatures lower.

And these glacial cycles are simply going to continue for another 5-25 million years. There is still much debate about this amongst the geological community, but until North and South America break apart again and that waterway returns we are going to be locked in this glacial-interglacial cycle.

Of course, if this lasts for 25 my, then it will not matter all that much because we are going to be heading into a new supercontinent and another global mass extinction. Where probably half of the planet will be largely uninhabitable.



Because ultimately, no matter what model the planet actually follows you can see the death of half or more species on the planet in the future geography no matter what form it ultimately takes.

 

[Anomalism]

Wouldn't that response be out of step with the northern hemisphere's response? Is that seen?

Hemispheric asymmetry is well supported. Northern Hemisphere ice sheets tend to dominate the magnitude of global ice volume change because they sit on large landmasses that can rapidly accumulate and lose ice, which strongly amplifies albedo feedbacks. That doesn’t mean Antarctica is out of step. Antarctic temperature, Southern Ocean circulation, and CO2 exchange all actively participate in glacial cycles, and records show leads and lags between hemispheres depending on the interval. The NH has more influence on the size of glacial swings, but the system is still tightly coupled.

 

[Anomalism]

You keep saying they are not the same mechanism like that means something. Once glaciation is triggered in the NH regardless of the mechanism, the feedbacks are the same.

Once large scale glaciation or deglaciation is underway, many of the same feedbacks operate regardless of how it started. That doesn’t make the initiating mechanism irrelevant. The question in paleoclimate isn’t whether ice albedo, CO2, and circulation feedbacks exist, it’s why the system keeps entering those regimes on orbital timescales instead of at random intervals or purely from internal variability. Different triggers do not have equal ability to reliably reproduce that pacing over hundreds of thousands of years, which is exactly why orbital forcing remains central even though the feedbacks themselves are shared

 

[Anomalism]

The NH dominates the equation. How the NH goes, so goes the world. I don't think anyone knows what the pacing is for changing currents. But what we do know is that the ocean can abruptly trigger glaciation and deglaciation in the NH so it can't be ruled out as the source.

The Northern Hemisphere ice sheets dominate the amplitude of global glacial-interglacial change once a transition is underway, but that doesn’t identify the mechanism that sets the long-term pacing. NH dominance explains amplification, not clock-setting. And while ocean circulation can trigger abrupt shifts within a glacial state, those events don’t match or generate the full glacial–interglacial cycle structure across multiple cycles. Nothing about NH dominance or abrupt ocean flips, by itself, establishes a mechanism that reliably produces the observed long-term pacing.

 

[Anomalism]

Yes, and where you see orbital clockwork, I see something less than clockwork.

That’s fair as a description of the uncertainty, but less than clockwork can be misleading if it implies the orbital signal is just incidental. The glacial record isn’t random or just loosely structured. It shows statistically consistent alignment with orbital frequencies over long periods, even though the response is nonlinear. So the disagreement isn’t really clockwork vs non-clockwork; it’s whether orbital forcing is the dominant organizing boundary condition that the nonlinear system is responding to, or just one influence among several competing internal modes with no privileged role in setting the long-term pacing.

 

[ding]

so what "triggers glaciation" in NH?

Loss of heat circulation from the Atlantic to the Arctic.

I don't accept orbital forcing because higher solar radiation in one part of the year due to tilt, or obliquity, means less solar radiation in the “opposite” part of the year.

 

[ding]

As somebody that has studied geology for decades, I see the pattern clearly. And it is related to this.



It is hard to see in almost any plate tectonics animation, but the cause of our current climactic conditions can be seen in the animation above at roughly 1 minute. Where once was a large gap between North and South America which allowed water to traverse freely between the Atlantic and Pacific allowed our planet to remain warm. Then around 10 mya that started getting restricted, forcing the global currents to shift and at the same time become colder because they were spending more time near the poles.

That restriction corresponds to Antarctica freezing over around 14 mya, and it being completely slammed shut with the rise of Panama corresponds with the complete severing of that current and the start of the current Ice Age.

I have long compared our current conditions to a sick individual going through cycles of fever and chills. The planet wants to be warmer, it was significantly warmer throughout most of the history of our planet. But the isolation of the oceans is locking the things that drive the warmer temperatures into much more constrained basins and forcing temperatures lower.

And these glacial cycles are simply going to continue for another 5-25 million years. There is still much debate about this amongst the geological community, but until North and South America break apart again and that waterway returns we are going to be locked in this glacial-interglacial cycle.

Of course, if this lasts for 25 my, then it will not matter all that much because we are going to be heading into a new supercontinent and another global mass extinction. Where probably half of the planet will be largely uninhabitable.



Because ultimately, no matter what model the planet actually follows you can see the death of half or more species on the planet in the future geography no matter what form it ultimately takes.

Yes, plate tectonics led to each pole becoming thermally isolated from warm marine currents.

 

[ding]

Hemispheric asymmetry is well supported. Northern Hemisphere ice sheets tend to dominate the magnitude of global ice volume change because they sit on large landmasses that can rapidly accumulate and lose ice, which strongly amplifies albedo feedbacks. That doesn’t mean Antarctica is out of step. Antarctic temperature, Southern Ocean circulation, and CO2 exchange all actively participate in glacial cycles, and records show leads and lags between hemispheres depending on the interval. The NH has more influence on the size of glacial swings, but the system is still tightly coupled.

I understand all that. NH dominates the climate of the planet for good reasons. That's not what I was asking though.

 

[ding]

Once large scale glaciation or deglaciation is underway, many of the same feedbacks operate regardless of how it started. That doesn’t make the initiating mechanism irrelevant. The question in paleoclimate isn’t whether ice albedo, CO2, and circulation feedbacks exist, it’s why the system keeps entering those regimes on orbital timescales instead of at random intervals or purely from internal variability. Different triggers do not have equal ability to reliably reproduce that pacing over hundreds of thousands of years, which is exactly why orbital forcing remains central even though the feedbacks themselves are shared

I wasn't arguing the initiating mechanism is irrelevant. You keep arguing timescales but the timescales changed.

 

[ding]

The Northern Hemisphere ice sheets dominate the amplitude of global glacial-interglacial change once a transition is underway, but that doesn’t identify the mechanism that sets the long-term pacing. NH dominance explains amplification, not clock-setting. And while ocean circulation can trigger abrupt shifts within a glacial state, those events don’t match or generate the full glacial–interglacial cycle structure across multiple cycles. Nothing about NH dominance or abrupt ocean flips, by itself, establishes a mechanism that reliably produces the observed long-term pacing.

We don't know that.

 

[ding]

That’s fair as a description of the uncertainty, but less than clockwork can be misleading if it implies the orbital signal is just incidental. The glacial record isn’t random or just loosely structured. It shows statistically consistent alignment with orbital frequencies over long periods, even though the response is nonlinear. So the disagreement isn’t really clockwork vs non-clockwork; it’s whether orbital forcing is the dominant organizing boundary condition that the nonlinear system is responding to, or just one influence among several competing internal modes with no privileged role in setting the long-term pacing.

Higher solar radiation in one part of the year due to tilt, or obliquity, means less solar radiation in the “opposite” part of the year.

 

[Old Rocks]

Higher solar radiation in one part of the year due to tilt, or obliquity, means less solar radiation in the “opposite” part of the year.

seems that the response to temperature changes occurs simultaneously at both poles;

"The LODE simulation results further demonstrate that the interaction of these sub-orbital cycles can produce abrupt temperature increases of 5°–15°C within decades to centuries, mirroring the rapid warming and cooling events recorded in Greenland and Antarctic ice cores. These simulations suggest that nonlinear feedback mechanisms amplify orbital and suborbital forcing, driving climate variability on millennial time scales. The emergence of high-amplitude oscillations at the beginning and end of each ∼11 kyr cycle and often 5.5 kyr cycle in the model supports the idea that threshold effects and internal climate dynamics play a crucial role in abrupt climate transitions."

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JD042810