I’ve seen this paper before, so I’m mostly just “commemorating” it here (and so I can find it easily again).
It is not particularly germane to our present moment (interglacial warm) as it focuses on the deep past (glacial cold), yet I think it is important to absorb some of what it says in our present context. We are “on the edge” ( ;-) of glaciation. We’ve had our 12,000 year interglacial run. The W/m^2 at 65 North is below warm stable, and we are in the “unstable” zone. At any time we can tip back into frozen. We can NOT have a tipping point into too hot. That happened 12,000 years ago about when insolation “way north” went “way high” and the mile high glaciers over Vermont and Chicago melted. Now we are in the sunset years and trying to hang onto a bit of warm, while the “metabolism” (insolation) has gone off a bit too far.
So “shortly” in geologic time, this paper describes what regime we will be in. That might be this Grand Solar Minimum (2020 to 2040) or it might be the next big down cycle in about 2300 AD. It is hard to say precisely because we are in the metastable zone before the stable cold this paper describes. On the solar front, we are in a cold cycle as of this “sleepy sun” episode. In terms of accumulate ice and snow, we are still in a warm cycle. But things can change. And, what this paper says, is that they can change rapidly and for specific reasons.
Please forgive the odd artifacts that cut / paste from PDF files seem to be plagued by.
Rapid changes of glacial climate
simulated in a coupled climate model
Andrey Ganopolski & Stefan Rahmstorf
Potsdam Institute for Climate Impact Research, PO Box 60 12 03, 14412 Potsdam, Germany
Yes. Models. Again. Look, I’m not adverse to models as a learning tool. “Models inform our ignorance”. What I am adverse to is believing models without testing them, repeatedly; or using them to say what MUST happen as opposed to “the model implies this might happen”. I ran a SuperComputer center the main work of which was running models. Moldflow for plastic mould making and a proprietary CPU model for a next gen product CPU chip. Models work for many things. (In the case of the plastic, it saved us about $250,000 / case design. About 90% of the time we cut correct dies first time. It was 10 hours of Cray and “right first time”. Except about 1 in 10 was not quite right and we’d do a rework to figure out why. This was with ONE fluid at ONE temperature in a FIXED mould geometry. Climate, by comparison, is a few dozen orders of magnitude less constrained…)
So they have a model. The good thing is that they use it properly, to see what KINDS of behaviours are LIKELY. It is a probability and interaction investigation. Things that it is hard to see without a coupled model. They don’t make the mistake of saying they have it exactly right and this is what must happen tomorrow. They use it as a way to surface unexplained behaviours (then we can look for them in the real world).
Abrupt changes in climate, termed Dansgaard±Oeschger and Heinrich events, have punctuated the last glacial period (,100 ±10 kyr ago) but not the Holocene (the past 10 kyr). Here we use an intermediate-complexity climate model to investigate the stability of glacial climate, and we find that only one mode of Atlantic Ocean circulation is stable: a cold mode with deep water formation in the Atlantic Ocean south of Iceland. However, a `warm’ circulation mode similar to the present-day Atlantic Ocean is only marginally unstable, and temporary transitions to this warm mode can easily be triggered. This leads to abrupt warm events in the model which share many characteristics of the observed Dansgaard±Oeschger events. For a large freshwater input (such as a large release of icebergs), the model’s deep water formation is temporarily switched off, causing no strong cooling in Greenland but warming in Antarctica, as is observed for Heinrich events. Our stability analysis provides an explanation why glacial climate is much more variable than Holocene climate.
Some key bits here. First off, it isn’t strictly accurate to say “but not the Holocene”. Yes, for those two specific definitions it is true, as they are based on specific physical observations. Yet Bond saw the same pattern in the Holocene, with different indications, and they are called Bond Events. It is pretty clear that the Heinrich Events are likely coupled to the D.O. Events with one being the warming spike just before the cold plunge. For Bond Events, we are already warm in the Holocene, so mostly we just notice the cold spike. Also, the ice sheet is gone so we see the pattern in different physical clues. So the first thing to get firmly in mind is that there is a roughly 1500 year cycle of a warm spike / cold plunge.
Why is widely speculated, but the astounding regularity of it pretty much rules out chaotic internal oscillations or other surface based phenomenon. The best probability so far is that it is driven by a lunar / solar / tidal interaction. Though a lot of folks argue over the exact details of the mechanism. (I’ve done several postings on that already). Suffice it to say that SOMETHING keeps happening on a semi-regular basis.
There is some evidence for a 1470 basic timing. Some for a bi-modal 1200 / 1800 year with the average being 1470, and it is often called the 1500 year cycle. There is also other evidence for a fairly strong 1000 year solar cycle. Good luck untangling all the interacting cycles…
The other “key bit” is that during a glacial time, the only stable state is the cold state. I would point out that during the interglacial, we seem to have a stable “warm state” with periodic cold plunges. My hypothesis here is that the globe is bi-modal with a cold state and a warm state based on Milankovitch cycle properties, and that during both, counter cycle changes can cause a temporary “switch” to the other state. But it isn’t stable, so swaps back in a couple of hundred years.
Notice the implication of all that climate history. “Climate” is NOT stable. It has ‘stable modes’ with strong oscillations away from them.
Given what I’ve figured out about our present stage in the Milankovitch cycles, we are in the metastable transition zone of insolation (orbital circularity, axial tilt, precession vs perihelion, etc.) so are particularly unstable. BUT, we are already at the warm limit, so that instability is ONLY to the downside into the next cold glacial. (The good news is that it takes 100,000 years for the mile high ice to collect. The bad news is that the weather can suddenly, in decades or maybe less, turn brutally cold and mostly stay there.)
Next I note that their model shows a sudden warming shows up in Antarctica, Greenland not so much. Given that we are seeing the exact opposite right now, a large expansion of Antarctic ice, it makes a fellow want to go “Hmmmm….”.
Then they make a “sop” to our “stable” Holocene climate. Well, it WAS stable for 10,000 years (modulo that Younger Dryas thing…) and we are now back into an insolation regimen much closer to that quasi-stable phase. I would assert that we are presently IN a metastable state, and the Little Ice Age was an example of that. Next “dip” will be worse. (No, not opinion. Based on how the orbital mechanics are slowly and inexorably taking us to ever less heat up North and into the next Real Ice Age Glacial. It simply must, by definition be worse next time.)
So what ought we to look for in changes between the warm and cold phases, as seen in their model (other than a swap of hot / cold in Antarctica…)?
Two main types of abrupt climate changes have punctuated the last glacial period: Dansgaard±Oeschger (D/O) events and Heinrich events1±8. D/O events typically start with an abrupt warming of Greenland by 5 to 10 C over a few decades or less, followed by gradual cooling over several hundred or several thousand years. This cooling phase often ends with an abrupt final reduction of temperature back to cold (`stadial’) conditions. D/O climate change is centred on the North Atlantic and on regions with strong atmospheric response to changes in that area, and shows only a weak response in the Southern Ocean or Antarctica. The `waiting time’ between successive D/O events is most often around 1,500 years, or, with decreasing probability, near 3,000 or 4,500 years (ref. 9). This suggests the existence of an as-yet unexplained 1,500-year cycle which often (but not always) triggers a D/O event.
Hmmmm…. “an abrupt warming of Greenland by 5 to 10 C over a few decades”. Where have I seen folks falling all over themselves about rapid warming in Greenland… and just how would we like “gradual cooling over several hundred or several thousand years”?
I note in passing the typical reference to a 1500 year quasi-cycle, but with occasional “skips” in the geologic record as sea level changed. So what was happening 1500 years ago… Oh, yes, the Roman Optimum was drawing to a close with all the warmth there, then, and with ports that are now located many miles inland all over the Mediterranean…
Then followed by a sudden cold plunge in about 534 A.D. at the start of The Dark Ages. These were described as being both physically dark, and emotionally dark and cold. It was a time of chaos as civilizations collapsed and the world got very messy. So lets take 535 and add 1500. 2035 A.D. (Or we could add 1470 and get 2005 A.D. about when the solar cycle took a break and the sun cut EUV output dramatically and said it needed a vacation…)
It sure looks to me like with the present series of loads of snow events all over the place, following a “blow off peak” in 1998 in temperature, that we’ve passed the end of the “Modern Climate Optimum” and the solar switch is flipped. Now we just wait for the latency to pass and for the physical state to catch up with the energy balance change.
Keep always in mind that cyclical nature, and the oscillatory regime nature of the planet; with both a cold and hot stable limit / bound and with rapid fluctuation away from it about every 1500 years on average (but with other periodic nodes as well at cycle times from 60, to 180, to 200, to 350 ish, to 710 ish to about 1000 years as a strong node, and even an 1800 year lunar/tidal node). Now marry that wobble character to a metastable context. Where, in the past Holocene, we could expect to be pulled back up to a nice warm optimum when the wobble ended, and where in a glacial we know the plunge back to cold is certain, we are now in a metastable state. It can “go both ways”.
Think on that for a minute.
The implication of this is pretty obvious. We need to do anything possible to bias the dice toward the warm side. Cold kills, and a mile of ice over Chicago is not a good thing. Similarly, having a bit of melt in Greenland is vastly preferable to a “year without a summer” in New England and rampant famines. BTW, the Oklahoma Land Rush shown in “How The West Was Won” movie was a result of folks simply abandoning farms in New England after snow in summer and dead lambs. This is part of our history, and we ought to understand it. Warm is good, cold kills.
Just ask all the folks moving to Florida and Texas and California if they think cold and snow is better… Or the folks in Boston this year.
Records from the South Atlantic Ocean and parts of Antarctica show that the cold Heinrich events in the North Atlantic were associated with unusual warming there (the `bipolar see-saw effect’10±12). Sediment data also suggest that changes in the Atlantic thermohaline circulation are crucial in these abrupt climate changes and it is difficult to imagine a mechanism for such dramatic and rapid temperature changes that does not involve large changes in ocean heat transport.
The idea of a “Global Average” is daft. Just insane on the face of it. We know that there is a bipolar see-saw. Now ponder for a moment. Presently the Antarctic Sea Ice is at an all time high. Hmmmm… So we’ve had a warm spike (that just ended) and Antarctic ice grew. No surprise. Now we’re into the rebound. That Arctic ice went “way low” is absolutely ordinary. What is being missed is that we’ve started the bipolar see-saw and that this oscillatory instability when we are biased to a cold plunge is NOT a good thing. And NOT because of “Global Warming”!
We’ve entered an oscillatory phase during a metastable state when a cold plunge is due and the most likely outcome. Oh Dear. We can only hope that we flip the coin and it comes up ‘warm’. “But hope is not a strategy. E.M.Smith”.
This paper goes on from there to look at “forcing” (God I hate that term – jiggering or biasing would be more honest) the model with fresh water influxes. I’d assert the giant thing they are ignoring is the huge tidal shift as the moon goes through cyclical shift (Saros Cycle) perhaps modulated by the exact seasonal match up.
The paper goes on to spend a lot of time looking at “fresh water events”, completely missing that it takes a long time for a bit of sun to melt a mile thick chunk of ice, and also missing that a shift of tidal mixing can cause nice warm rains that work much faster. IMHO, flawed, but showing interesting dynamics. Pointing out the sensitivity to outside shifts, even if they got the wrong one.
So spend some time reading it, but spend more time thinking about “metastable” and “warm rain vs cold snow”. Then look at our present circumstance. Sleepy sun. Low UV. More cosmic rays. More cold snow. Warm spike in the N.H. coming to an end, to be followed by the inevitable cold snow events,
We are, quite certainly, headed into a cold excursion. The one thing that is entirely unknown is the outcome. Will we bounce back up to a return to the warm cycle lid? Or start that long next plunge into the next Ice Age Glacial? Absolutely nobody knows. That is the very meaning of “metastable”.
I dearly hope that the next down spike is in about 2300 (one half bond event past the Little Ice Age) and not now as one Bond Event Cycle after 535 A.D.. Yet, both Half Bond Events and full on Bond Events are cold excursions. The only questions are “how far” and “how unstable to the downside”?
This paper implies that, as we are well past the warm stable point, any downside wobble can be very very bad indeed. It says that during the glacial regime, things are particularly unstable, and we are well out of the stable warm zone in terms of solar input / heating of the northern hemisphere.