On “Trap-Speed”, ACC and the SNR

Guest post by William McClenney

“Trap-Speed”:

We will initiate this discussion by looking at some of the early, and then later, recognitions of some of climate change’s “best lap times” in terms of sheer speed. Perhaps one of the more poignant moments in all of climate science occurred in 1992, documented by John D. Cox, writing in “Climate Crash: Abrupt Climate Change and What it Means for our Future (John Henry Press, an imprint of the National Academies Press, ISBN: 0-309-54565-X, 224 pages, 2005), which describes the initial discovery of Abrupt Climate Change (ACC) and also introduces a main character, Dr. Richard B. Alley:

“They knew they had the critical layer of ice in their snow cave [where the ice cores were first processed-wm]. Wanda Kapsner, a Penn State graduate student, had been taking thin sections about every 20 meters along the lengths of core laid out in the cave. She told Alley, ‘This section is in Holocene ice and the next section 20 meters down is in Ice Age ice, and so between these two is where you’re going to find it.’”

“This team of scientists was about to complete their six-week stint at Summit, and a new team was about to take its place. So it was up to project leader and paleoclimatologist Paul Mayewski to decide which team was going to handle this important ice. On hearing the news from Kapsner, Mayewski told Alley, ‘Fine, before we get out of here, we’re going to do that ice.’”

“The ice that had formed from falling snow during the transition from the last of the cold, dry, windy ice ages to the first of the warm, wet calms of the modern 10,000-year-long Holocene climate is 1,678 meters, just over a mile, down the GISP2 core. Rendered in ice, what exactly would it look like, this boundary of epochs? The young American scientists had read the literature from Chet Langway, Willi Dansgaard, Hans Oeschger, Wally Broecker, and others, and they had heard from the Europeans, who were about a year ahead of them in drilling at Summit. Yet still they were not entirely prepared for what they saw that day in the ice, for the suddenness of it.”

“’You did not need to be a trained ice core observer to see this,’ recalled Alley. ‘Ken Taylor is sitting there with the ECM and he’s running along and his green line is going wee, wee, wee, wee—Boing! Weep! Woop! And then it stays down.’ Dust in the windy ice age atmosphere lowered the acidity of the core to a completely new state. ‘We’re just standing there and he just draws a picture of it,”’Alley said.”

Spontaneous celebration was followed by a sudden and unexpected quiet. ‘I think we cheered,’ recalled Alley, ‘and then we were all a little sobered. Because it was just so spectacular. It was what we’d been looking for, and there it was, and then we’re sitting there. Holy crap.’”

“The instant of recognition that summer of 1992 had a raw feel to it, although eventually the disquiet would find concrete expression in numerous articles and presentations as the scientists became accustomed to the large truth of abrupt climate change and immersed themselves in its fine details. Alley recalled later: ‘Those of us who were down there in that trench at that time knew right then that our picture of the world had changed. There’s a whole bunch of us who came out of that ice core project who have since dedicated ourselves to understanding abrupt climate change.’”

“In the GISP2 science trench, the tray holding the section of core rolled down the assembly line and then it was Alley’s turn at the ice. “It slides across in front of me and I’m trying to identify years: ‘That’s a year, that’s a year and that’s a year, and—woops, that one’s only half as thick.’ And it’s sitting there just looking at you. And there’s a huge change in the appearance of the ice, it goes from being clear to being not clear, having a lot of dust.”

Paper after paper began to roll off the scientific presses from 1992 on, and just like the unfolding recognition of plate tectonics which preceded it by a few decades, it was literally riveting for all of us geologists fascinated by the Quaternary. So we get our first trap-speed: climate can switch abruptly from its cold to its warm state in just one year. Our first peg on the lower-end of natural noise.

Stocker and Marchal (2000) begin their discussion with this:

“Among the archives recording past climate and environmental changes, ice cores, marine and lacustrine sediments in anoxic environments, and tree rings have seasonal to annual resolution. Changes in dust level (1), snow accumulation (2), summer temperature (3), and indicators of the productivity of marine life (4) suggest that some of the climate changes have evolved on time scales as short as a few years to decades.” (“Abrupt Climate Change in the Computer: Is it real?” (PNAS, vol. 97, no. 4. February 15, 2000, pp. 1362–1365)

By 2002, we have this from the National Research Council:

Recent scientific evidence shows that major and widespread climate changes have occurred with startling speed. For example, roughly half the north Atlantic warming since the last ice age was achieved in only a decade, and it was accompanied by significant climatic changes across most of the globe. Similar events, including local warmings as large as 16°C, occurred repeatedly during the slide into and climb out of the last ice age. Human civilizations arose after those extreme, global ice-age climate jumps.”

“The new paradigm of an abruptly changing climatic system has been well established by research over the last decade, but this new thinking is little known and scarcely appreciated in the wider community of natural and social scientists and policy-makers.” (“Abrupt Climate Change – Inevitable Surprises”, Committee on Abrupt Climate Change, National Research Council of the National Academy of Sciences, 2002, ISBN: 0-309-51284-0, 244 pages, Richard B. Alley, chair).

We will step a little closer in time and take a look at a rather fascinating ACC event.

The Younger Dryas:

Proxy and isotopes become more difficult to work with over time, carbon 14 gets us back some 50kyrs, but no further. The longest and presumably best ice cores come from Greenland and so far extend no further than 135kyrs or so. So we will begin to examine some of the better resolved climate change trap-speeds from the Younger Dryas.

From two National Academies Press publications:

“The ice was always melting back. Rivers were getting wider and flowing over new lands. Warm times were lasting longer. Forests were growing larger and richer, as were the big grasslands and their wild grains. Some 12,000 years ago, hunters were in the embrace of a stable, congenial climate stretching back farther than memory, perhaps farther than the stories told by the elders. For hundreds of years, the ice had been shrinking and a large swath of landscape had been bathing in steadily increasing warmth. In the fertile lands of West Asia, clans of an ancient people that would become known as the Natufians had long been accustomed to the good hunting of game and the easy gathering of fruits and wild grains. This was the way of the world for people 12,000 years ago. Nothing in the sky or the sea or on the land and nothing in memory warned them of what was to come. The change in climate was a surprise of life-bending power, as if the whole world turned against the clans. Cold, dry winds began sweeping the countryside, withering every living thing in their paths. First the fruits were lost and then the grasslands, and eventually the forests were driven back. The rivers shrank and some became choked with advancing ice. Without warning or recognition, in just a few years, a colder, harder, shorter, and more difficult way of life set in. From beginning to end, as far as the Natufians were concerned, the time of wind and cold lasted forever. Like the old time of warmth and plenty, the hard new climate stretched out beyond memory, holding humanity in its grip for something like 470,000 days.

What in the world happened? Why did the climate over much of Earth so suddenly reverse itself? What is it about the way of the world that makes such a thing possible? Why did this crippling cold, windy, dry regime hold sway over the sparsely populated lands of the Northern Hemisphere for 13 centuries?”

Asks John D. Cox in “Climate Crash”. Three years before, the National Research Council, of which Richard Alley was chair, stated:

“Briefly, the data indicate that cooling into the Younger Dryas occurred in a few prominent decade(s)-long steps, whereas warming at the end of it occurred primarily in one especially large step (Figure 1.2) of about 8°C in about 10 years and was accompanied by a doubling of snow accumulation in 3 years; most of the accumulation-rate change occurred in 1 year. (This matches well the change in wind-driven upwelling in the Cariaco Basin, offshore Venezuela, which occurred in 10 years or less [Hughen et al., 1996].)”

“Ice core evidence also shows that wind-blown materials were more abundant in the atmosphere over Greenland by a factor of 3 (sea-salt, submicrometer dust) to 7 (dust measuring several micrometers) in the Younger Dryas atmosphere than after the event (Alley et al., 1995b; Mayewski et al., 1997) (Figure 2.1). Taylor et al. (1997) found that most of the change in most indicators occurred in one step over about 5 years at the end of the Younger Dryas, although additional steps of similar length but much smaller magnitude preceded and followed the main step, spanning a total of about 50 years.”

The above quotes from page 27 of “Abrupt Climate Change – Inevitable Surprises” (referenced above).

Richard B. Alley, NRC chair of the Committee on Abrupt Climate Change, states in Quaternary Science Reviews (2004):

“In the case of the termination of the Younger Dryas cold event, for example 1/3 to 1/2 of the entire 10,000-year deglacial warming in Greenland was achieved in order of 10 years (Cuffey et al., 1995; Severinghaus et al., 1998), with most of the accumulation-rate change apparently in a single year (Alley et al., 1993). The scaling of 1/3 to 1/2 the deglacial change in about a decade probably applies in many places (Alley, 2000). Any event for which rate of change is anomalous by two to three orders of magnitude merits attention. Older events were even larger, with a rapid shift of about 16 C in Greenland in one case (Lang et al., 1999).”

Steffensen et al (Science, vol. 321, 1Aug2008) abstract it thusly:

“The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.”

More recently the Akkadian Empire under Sargon (2,300-2,200 BC), mankind’s first empire ever, succumbed to climate change that happened rather suddenly. A 300 year long period of drought struck this nascent civilization and toppled what turned out to be only a 100 year empire. The Old Kingdom of Egypt and the Harappans of the Indus Valley suffered a similar fate 4,200 years ago, succumbing to an abrupt drought that ended those civilizations, with Egyptians “forced to commit unheard of atrocities such as eating their own children and violating the sacred sanctity of their own dead (Fekri Hassan, 2001)”. The Mayans had pretty much the same luck with three periods of extreme drought at 810, 860 and 910 AD. Sadly just two years after the last drought, which saw 95% of the Mayan population gone, wet years returned to the Yucatan.

A reconstruction from fossil algae in sediments from Drought Lake in North Dakota of the past 2000 years found that dry conditions were far and away the rule in the High Plains, with the Dust Bowl conditions of the 1930’s one of the lesser dry spikes found in the record.
The Wisconsin glacial, which preceded the Holocene, the interglacial in which all of human civilization has occurred, is littered with ACC. D-O oscillations average 1,500 years, and have the same characteristic sawtooth temperature shape that the major ice-age/interglacials do, a sudden, dramatic, reliable, and seemingly unavoidable rise of between 8-10C on average, taking from only a few years to mere decades, then a shaky period of warmth (less than interglacial warmth), followed by a steep descent back into ice age conditions. Each D-O oscillation is slightly colder than the previous one through about seven oscillations; then there is an especially long, cold interval, followed by an especially large, abrupt warming up to 16C (a Bond cycle). During the latter parts of the especially cold intervals, armadas of icebergs are rafted across the North Atlantic (Heinrich events), their passage recorded reliably by the deep ocean sediment cores which capture the telltale signature of these events in dropstones and detritus melted out of them.

“The ice age ended in one year” according to Dorthe Dahl-Jensen, professor at the Center for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen:

“We have analysed the transition from the last ice age to our current warm interglacial period and there is such an abrupt change in climate that it is as if someone just pushed a button”

What should be fairly apparent is that in terms of sheer speed, major natural climate change can occur in the 1 year bracket, the bottom end of the natural noise range, and not just at the glacial terminations. We see evidence of many cycles, small and large, that occur from 3-7 years (El Nino range), on the decadal (AMDO/PDO) to millennial (D-O) scale. Not to mention the 100 million year major ice age cycles. Therefore, in order to qualify as a signal, and subsequently recognizable as anomalous, the signal must somehow exist outside of a range spanning 1-100,000,000 years.

SNR:

From Wikipedia:

“Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure used in science and engineering to quantify how much a signal has been corrupted by noise. It is defined as the ratio of signal power to the noise power corrupting the signal. A ratio higher than 1:1 indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any form of signal (such as isotope levels in an ice core or biochemical signaling between cells).”

Think of SNR as possibly the simplest statistical test.

This time we will work backwards from recent time (present to 70 million years ago [mya]). Mainly in terms of the two primary components of climate change, temperature and sea level. This part will be primarily visual, with the intent being to exercise your perhaps newfound skills in discerning signal relative to background.

[In the interest of full disclosure, not all of these graphics I thought at the time to reference (when jpeg’ing them from the pdf’s), or after downloading them from wherever.]

So we will start with the projected anthropogenic signal from the IPCC’s Assessment Report 4 (AR4) (2007). This is Figure 10.33 from page 821 of Chapter 10:


SRES marker series A1F1’s upper error bar comes in at about 0.59 meters, about 2 feet, to 2099. To be prudent, we might round that up to 0.6 meters for the AGW “signal”.


I got this from the C3 website some time ago, but I do remember going to the source and digging up the data. Assuming the 75 year smoothed Law Dome 1,000 year record evinces the LIA and MWP, then the recent thousand-year noise is nominally say 1.5C, but also potentially inclusive of 3.1C. High SNR of about 0.4:1 (0.6/1.5), or 40% of the noise level, to low SNR of 0.2:1 (0.6/3.1), or 20% of the noise level. Not anomalous (need >1:1).


Post “8.2k event” sea levels from Rio Grande do Norte, Brazil. Late Holocene sea level noise range of maybe 6 meters, -2 to +4 AMSL. A SNR of 0.1:1, or signal at 10% of the noise level. Not anomalous.


Here we see the range perhaps -32.4 to -28.7, or a temperature noise envelope of 3.7C through the majority of the Holocene interglacial. The “8.2k event” and the Holocene Climate Optimum paired and evident. As is the rocky ride down since the Minoan Warming. SNR similar but lower still than the 1kyr comparison (0.16:1, 16% of the noise). Not anomalous.

In the majority of the Holocene, the noise level is simply too high to accommodate recognition of the AR4 worst case AGW “signal” scenario. If we take what is widely recognized as the dual-thermal sea level maxima at MIS-5e (6 meters) then at the end-Holocene, the SNR degrades to just 10% of the latest post-MPT end-interglacial noise. Not anomalous. Beyond this point, SNR itself becomes subject to the larger post-MPT glacial/interglacial switch between the warm and cold states which have dominated climate for the past ~800kyrs or so.

As we exit the Holocene (stage left), we have this interpretation of our present interglacial’s sea level from “Holocene sea-level fluctuations inferred from the evolution of depositional environments of the southern Langebaan Lagoon salt marsh, South Africa, John S. Compton, The Holocene 11,4 (2001) pp. 395–405 (sorry, best reference preserved in the downloaded paper I found online August, 2009).


More sea level “noise”, this one going back 200kya.


The Eemian, the last interglacial, sea level history from the Red Sea (Rohling et al, 2008, Nature Geoscience, vol. 1, p. 39, January, 2008).


Even on things which have happened, the science is not that particularly well-settled.


A look at the Eemian (MIS-5e or 5.5) to termination T3 (prior to the MIS-7 interglacial) from Bard et al, 2002 (Earth and Planetary Science Letters 196, p. 135-146).


The past 4 “extreme” post-MPT interglacials (but dating back to the MPT). Interglacial maxima over the past 800kyrs.


Post-MPT sea level interpretation.


The post-MPT from Jouzel et al, 2007 (www.sciencemag.org, Science, vol. 317).


The past 5 million years.

Again, I do not remember from what paper I extracted this. Note the gradual, post-PETM evolution of climate. Noise, at even more alarming levels is apparent not only in the primary decline, but in the range about the late mean. This takes us out to 70mya.

Summing Up:

Now that you have taken the “wild climate ride”, which just predates the extinction of the dinosaurs to present, the Holocene trapping with a top SNR of just 0.4:1, ACC which traps in the one year bracket, and with respect to the definition of an anomaly, what would your present estimation be of the AR4 AGW worst-case “signal” prognostications?

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75 thoughts on “On “Trap-Speed”, ACC and the SNR

  1. I agree with Phil, many thanks to the author.

    Looking at Antarctica, the Palmer Deep, Domack et al. found clear oscillations. Those of 200 and 400 years were considered to be caused by solar variability, while one of 1800 years may be related to lunar tidal changes.

    But what caught my attention was the comment that there is ‘an as yet undetermined multidecadal forcing phenomenon that operates in the SE Pacific sector of the southern ocean.’

    http://www.agu.org/journals/ABS/2002/2000PA000602.shtml

    Wonder if we can pinpoint the location and cause of this forcing, and did the Holocene interglacial begin in the SH?

  2. Fascinating article. I especially appreciate the description of Bond events and the D-O events.

    The normal state of affairs is a much colder climate. We have been very fortunate to be living in such a pleasant and temperate climate. A degree or two warmer would be even better, but the odds don’t favor that outcome.

    Here’s an animation previously posted at WUWT, showing successively longer time periods. Warmth is good. Cold kills.

  3. The most striking thing about this article is the fact that abrupt climate chance is associated with the transitions from glacial maxima to inter-glacial conditions. By contrast, the transitions from inter-glacial to glacial maxima seem to occur gradually over tens of thousands of years, often in steps.

    Here is my (highly-speculative) reasoning as to why this should be so :

    My theory is that the decay of continental ice sheets begins at their centre, and commences even before the glacial maxima is reached. The reason for this is precipitation-starvation. In short, conditions approaching the glacial maxima become so cold that little or no precipitation occurs, and without precipitation ice-sheet accumulation is impossible.

    The ice-sheets still continue to expand and accumulate at the edges however, particularly at mid-latitudes, because there is still a plentiful supply of moisture and conditions are plenty cold enough for nearly all the precipitation to fall as snow.

    This means that when the time comes for the Earth return to an inter-glacial phase, a disproportional amount of the ice locked up in the continental sheets is located at mid-latitudes. Exactly where it is most vulnerable to rapid melting in a warming world………

    Thoughts?

  4. Smokey, always like your posts. you must be totally a neat freak!

    Anywho, was just wondering if you had an updated version of your first chart (Bond events), cuz one of the points made by the pro side is that the warming in the past few decades has been faster then at any other recorded time. When eyeballing that chart that you supplied of the last 10k years, there are at least 2 other periods where the warming was on the same scale, but as you know, the chart only goes to 1950.

    Thanx!

  5. That the climate can change so abruptly is yet another indication that it isn’t just orbital mechanics that causes them. Orbital mechanics simply doesn’t change that dramatically in that short of a period and how it can go from progressively colder periods to suddenly interglacial warmth in as little as 10 years is simply boggling.

    The change is obviously dramatic and fast.

  6. The old ones knew the cold would not make the food crops larger, so they left the canyon.

    Chaco you.

    http://www.chaco.com/park

    google Chaco Collapse….\
    Now would they have been in danger if it was getting warmer?
    Would they have been doing more crops for food if it was getting warmer?
    Seeds do not like to germinate when cold.

    Blind studies/guides do not work out that well if the blind are the ones who see the way forward for others.

  7. “…And there’s a huge change in the appearance of the ice, it goes from being clear to being not clear, having a lot of dust.”

    What was the TIME of this that she is talking about?

    I am active in the Younger-Dryas Impact Event discussion (totally as a lay person), and I have to wonder is she seeing the onset of the Younger-Dryas interstadial – which DID come on very quickly – or is she seeing the earlier onset of wamth – which was relatively slow?

    Does anybody know what year/age she is talking about?

    This could be an important addition to the discussion there. It may likely already be included, but in case it isn’t…

  8. My interpretation of this somewhat obtuse essay, offered as a rhetorical question:

    1. Abrupt Climate Change (ACC) has possibly occurred in the past, both upward and downward. I say possibly because the proxies themselves have significant sampling error (noise) in both the isotope and time range. Still, there seems to be evidence that swings of as much as 16°C have occurred (in Greenland) over a short time period (a few decades or less).

    2. During the Holocene the temperature swings have been rather tiny compared to D-O events and glacial-interglacial oscillations of the last 800 ky. Perhaps as fast, but certainly not as large in amplitude.

    3. The IPCC AR4 worst case AGW scenario is not stated, but I think it may be around +2°C over the next 100 years. Please correct me if I am wrong about that.

    4. If that temperature shift should occur, it would be very minor compared to apparent swings in the paleoclimate record.

    If that was the message (I apologize for my thickness), then even the worst case scenario is nothing to be alarmed about. As Smokey intimates, warmer is better anyway.

    What may be worth some worry is the potential for a sudden global temperature drop of 3°C or more over a period of a decade or less. Such rapid drops (ACC) have previously occurred in the Holocene (the 8.2 ky event), and even more pronounced rapid drops may have occurred with D-O events in the recent geologic past.

    Also, the mechanism behind ACC events is obscure. If, as some conjecture, relatively small solar insolation changes trigger ACC events via rapid albedo changes and/or rapid melt of continental ice sheets into oceans, then those are unlikely to occur now. There’s not much continental ice left to melt (no upward ACC) and the Earth’s albedo is unlikely to increase rapidly (no downward ACC).

    That’s my interpretation. Please feel free to correct me. Nicely, if possible.

  9. What does it look like? It looks like unprecedented warming, and cooling and in-between periods too. Or something…

    Is it still unprecedented? Did I get that right? Does climate change?

    I am sooooo confused!

  10. “cold dry winds” Sure enough, that would do it. A few days ago, here in Phoenix, it had rained earlier, but the humidity was low and a cold wind was blowing (I could tell by the large static charge that would give me a jolt when I grounded myself that humidity was low), and while not even close to the freezing point, the rain that had collected in the boat’s cover froze over quite well. Took little time at all, water a bit more than a foot deep. Must have been a shortage of CO2 that day..

  11. Off topic: In the last aired episode of ‘V’, the TV series, the aliens are confronted by the humans with why they reddened the skies. At the start of the episode the aliens mention that they are monitoring the top environmentalists to see if they don’t reach a conclusion. But then there is a Dr. Watts «whose research is approaching dangerous proximity to the truth». I laughed!

  12. An awe inspiring essay, William McClenney (and by default, Anthony). Thank you.
    From the gems within it I choose to quote but one:

    “From beginning to end, as far as the Natufians were concerned, the time of wind and cold lasted forever. Like the old time of warmth and plenty, the hard new climate stretched out beyond memory, holding humanity in its grip for something like 470,000 days.”

    This quote alone makes the fraud of AGW obscene; and the carpetbaggers criminals. History will not treat them kindly — small comfort for the suffering they have already, and will continue, to inflict upon the peoples of this world.

  13. they should ask L Gore what he thinks about the ice core results . the answer would be they would not have clue what they are doing

  14. Over the past 2-3 million years, since plate tectonics has closed the land bridge between North and South America, the continental and ocean basin structure has been such that the “gulf stream” has been a quasi-stable system, a “strange attractor” in the vernacular of the 1990’s chaos theory. When the Gulf Stream is flowing (now) we are in the warm state, the interglacial high energy and less probable state which last for ~ 10,000 years. When the Gulf Stream is turned off we go into an ice age, a lower energy more stable state which last for ~ 100,000 years. The transition from one state to another could be quite rapid (diameter of the earth / ocean current speed < a year).

  15. So this shows we had 8 degrees warming occur in just a decade only a few thousand years ago. Yet the 0.7 degrees warming over the last 150 years is ‘unprecedented’?

    And what stopped that 8 degrees runaway warming continuing and frying the planet to a crisp? Because one thing is certain, mankind had no effect whatsoever on either triggering the rapid warming or what stopped the warming.

  16. Anything is possible says:
    January 5, 2011 at 8:52 pm
    The most striking thing about this article is the fact that abrupt climate chance is associated with the transitions from glacial maxima to inter-glacial conditions. By contrast, the transitions from inter-glacial to glacial maxima seem to occur gradually over tens of thousands of years, often in steps.

    Here is my (highly-speculative) reasoning as to why this should be so :

    My theory is that the decay of continental ice sheets begins at their centre, and commences even before the glacial maxima is reached. The reason for this is precipitation-starvation. In short, conditions approaching the glacial maxima become so cold that little or no precipitation occurs, and without precipitation ice-sheet accumulation is impossible.

    The ice-sheets still continue to expand and accumulate at the edges however, particularly at mid-latitudes, because there is still a plentiful supply of moisture and conditions are plenty cold enough for nearly all the precipitation to fall as snow.

    This means that when the time comes for the Earth return to an inter-glacial phase, a disproportional amount of the ice locked up in the continental sheets is located at mid-latitudes. Exactly where it is most vulnerable to rapid melting in a warming world………

    Thoughts?

    an interesting idea AIP, but doesnt it ignore the fact that it’s weight that forces the snowdome down. Stop adding weight, and it will stop moving down.

    EO

  17. It can change suddenly …. and pigs fly?

    It might not be what they think. If e.g. the temperature went through a warming period of perhaps several hundred years, the ice might melt repeatedly wiping from the record the whole period of gradual change from one climate type to another. Not until the average temperature dropped again would the ice start building up resulting in an apparent dramatic change from one climate type to another — simply because the record from intermediate years had melted!

    Indeed, if the ice melt zone was one that accumulated dust, the dust would preferentially melt this area each and every year until the first year that the temperature was cold enough again to prevent the ice melting through to the dust layer after which this dust layer would be buried and have no effect.

    Worse still (in terms of any record of the event), this layer of dust may have been removed by entirely natural water flow … so that a zone of preferential melting due to surface dust, suddenly starts to build up ice with absolutely no record of the change from a single ice core!

  18. I agree with the S/N analysis – a point I’ve been making particularly regarding the 1/f noise in the climate signal for years – but I found the article difficult reading are there supposed to be graphics? If so why can’t I see them?

  19. It is indeed scary to know that the planet can plunge into an ice age in one generation or shorter. Obviously something dramatic happened. But what? Yellowstone blowing up?

  20. Figure 3 is incorrect. It says “years before present (2000)”. That should be “years before present (1950)”. Also as it ends 95 years before 1950, it ends in 1855 so the graph is missing the temperature change since then (which I am sure is quite significantly in the upward warming direction)

    More importantly the changes occurring now and into the next century don’t have to be anomalous to cause problems. Who would want sea level to rise 5 meters, even though that kind of change is comfortably within past natural variation (before human civilization existed)?

    This article is very good however at conveying the fact that climate can indeed change a great deal very fast. It has done so in the past many times. The Earth’s climate is not protected by negative feedbacks and stability, it’s just an accidental set of interacting systems that can be thrown out of whack.

    Which is in my mind the principle reason to want to reduce CO2 emissions. Prodding the angry beast of climate with ever rising levels of CO2 is unwise.

    On that subject the article explores temperature and sea level records, but hasn’t explored the CO2 record which is probably the record showing the most anomalous recent changes due to human activity. Plot CO2 over the past 800,000 years and the recent spike occuring in the past 2 centuries is highly anomalous. Go back further (tens of millions) and there is no evidence CO2 has ever in Earth’s history shot up as fast as we have, and are, raising it. If I recall correctly even the CO2 rise during the PETM was slower than the current rate of rise.

  21. William McClenny,

    Hope I wasn’t being rude. I thought that a great post.

    “In the majority of the Holocene, the noise level is simply too high to accommodate recognition of the AR4 worst case AGW “signal” scenario.”

    And what is more likely the true signal, I feel makes the AR4 look considerably exaggerated.

  22. No-one seems to have considered where the heat came from (for warming) or went to (for cooling). Furthermore, rapid warming or cooling, on a global scale requires large amounts of heat in/out – has anyone calculated what the rates are?

    My guess is that, for the rates of change quoted above for ‘abrupt climate change’, these numbers are unfeasibly large.

  23. If you lived on top of the Greenland ice sheet at 4 kms high 12,800 years ago, with the average temperature of -32C, maybe temperatures for you dropped by -8C in the Younger Dryas event. Like they had rapidly dropped -10C, 1,500 years earlier in the Older Dryas event.

    But the changes in the North Atlantic or Anatarctica or in the rest of the world were only one-quarter as much. I don’t like how the Younger Dryas event is portrayed as such a scare story when the Greenland ice sheets show at least 25 similar events in its 110,000 year long ice core (which is actually calibrated). It is a normal ocurrence on top of the Greenland ice sheet at 4 kms high during the ice ages.

    Furthermore, the ice cores show it took 400 years for the full temperature change to occur in both events, so it was not a sudden one-year drop. It is an exaggeration.

  24. Sorry but I don’t understand the point of this posting – it just looks to be posing rather a silly riddle.
    As Anything is Possible says: “The most striking thing about this article is the fact that abrupt climate chance is associated with the transitions from glacial maxima to inter-glacial conditions.” I agree.
    The last time I looked out the window we were in an interglacial. So are we now back in the 1970’s, talking of Abrupt Climate Change to a new ice age expected within the next few years? I thought we were generally discussing CAGW – bring it on, to stop the cold!
    I’m a simple-minded soul. In the last ~1m years BCE there have been regular ~100ky glaciations probably due to Milankovitch orbital cycles, during which sea levels and CO2 have both regularly risen and fallen. During the glaciations temperatures have been perhaps 7C cooler than at present.
    This has some similarity to an engine turning over – and having done at least 10 revolutions we see that the engine is quite stable; nothing has fallen off or gone seriously out of control.
    We have now – innocently – caused a perturbation in CO2 levels (which I believe mankind will anyway have the technology to bring under control again in another century or two – the blink of an eye in astronomical terms). The effect of CO2 on temperature is logarithmic which turns any exponential power into a straight line slope. While no-one can yet rigorously prove it I simply can’t believe that this minor blip has affected the inherent stability of the system as operating over the last 1m years, and that we don’t have plenty of time to check out that this is so. That’s my view anyway!

  25. “Which is in my mind the principle reason to want to reduce CO2 emissions. Prodding the angry beast of climate with ever rising levels of CO2 is unwise.”

    As dangerous as prodding a horse with a microscopic feather.

  26. Wait a minute. Are they talking about climate change prior to the industrial revolution? Now I thought only humans could change the climate. /sarc

  27. “Go back further (tens of millions) and there is no evidence CO2 has ever in Earth’s history shot up as fast as we have, and are, raising it. If I recall correctly even the CO2 rise during the PETM was slower than the current rate of rise.”

    Which shows that vast and rapid climate changes, (far in excess of the tiny 0.7 degrees rise of the 20th century, even IF it was that much), are NOT associated with and cannot possibly be caused, or driven, by CO2.

    The current warming is not outside the normal noise of natural variability.

  28. “No-one seems to have considered where the heat came from (for warming) or went to (for cooling). Furthermore, rapid warming or cooling, on a global scale requires large amounts of heat in/out – has anyone calculated what the rates are?

    My guess is that, for the rates of change quoted above for ‘abrupt climate change’, these numbers are unfeasibly large.”

    Agreed, and we are not seeing such rates or the vast differences in ‘heat in vs heat out’ currently as would have been present at those times of very rapid and extremely large climate change in the past.

  29. Being partially deaf I am particularly aware of SNR [signal to noise ratio.]

    In the climate debate I have yet to locate the signal; except to conclude that there appears to be no anthropogenic problem.

    What puzzles me, however, is why our scientists seem to concentrate on the measurement of global temperature when surely they should be concerned with matters of global Albedo and Emissivity?
    After all it is these two factors which determine the temperature; not necessarily the other way round.
    Currently the perceived ratio of Albedo to Emissivity is approx. 0.49 and we know, courtesy of Mr. Stefan, that; should this ratio increase then the planet is cooling and visa versa.

    The problem, of course is the difficulty of determining from the broadband radiation data which is due to Albedo and which to Emissivity. Am I right?

    Any suggestions?

  30. I had a thought similar to Mike Haseler who posted at 12:42 am.
    To me, deciphering ice cores is similar to understanding geological strata. If rock strata have been removed and new strata deposited on top, one cannot know what happened before the removal. I am interested in the detail of how the ice core strata interpretation was made and determined to be so abrupt when the climate changed from cold to warm.

  31. onion says:
    January 6, 2011 at 1:21 am

    Which is in my mind the principle reason to want to reduce CO2 emissions. Prodding the angry beast of climate with ever rising levels of CO2 is unwise.”

    Why? It has not been demonstrated that a warm period is an undesirable event. ALL evidence points to cold periods being a time when whole civilisations and species collapsed. Warm periods have seen all life flourish.

    Just what is it you seek? A cold, dry and barren world with little life? Or a warm, wet environment, teeming with a diversity of life? And what is with this “angry beast” of climate? Are you appealing to something here? Like a deity? You must be a single male, as married guys are used to dealing with an angry and jealous god; she’s named the Mrs. I have seen the angry Gaia and she can be dealt with! Nothing to get all bunched up over. Besides, I am of the belief we can’t control the climate any more than we can move the moon. Maybe one day, just not for a good long while.

    Just settle down and enjoy the ride.

  32. @TimC says:
    January 6, 2011 at 4:53 am “probably due to Milankovitch orbital cycles”

    Probably Not !

    The problem is any cooling is extremely dangerous (devastating) for humanity and a doubling or tripling of CO2 with a possible resultant 0.5 to 2.0 degree C rise poses no threat to humanity.

  33. A fascinating and well written article.
    All the Neanderthals must have driven their V8 SUVs over a cliff, in squadrons and in unison. Only CO2 from vehicle engines and power generating plants can seriously change the climate – or did I get that wrong?

  34. The specifics of the changes are not really the point of the article. It is that their simple existence, and their ranges, constitute a fluctuating background (noise) which makes attribution of any current or upcoming changes impossible. Unless the “noise” is subtracted from the record by accurate and detailed explanations of those variations.

    If we had that degree of comprehension of the climate system then extrapolation of the effects of our own “interference” with its processes would be almost trivial. Since we do not, it is unfeasible.

    If any dramatic swings occur (which seems historically inevitable), then we will, as in the past, adapt, either well or poorly. All resources and time spent “pre-mitigating” will have about the same effect and value as all the efforts of early cultures to propitiate the weather gods and the ancestors: none on the weather, but serious misdirection and depletion of available energy, materiel, and attention to real survival concerns.

  35. It seems to me that the salient point here is that it’s easy (relatively) to pick a continuing signal out of background noise if you know what signal looks like – but the problem gets exponentially harder as you add conflicting signals and becomes impossible when both noise and signal sets are human contaminated.

    We know, for example, how to pick up and decode a signal from a probe at the edge of the solar system largely because we know what distinguishes it from noise and because there’s only one.

    We could not, however, recognize as signals comparable wider band energies emitted by multiple entities staggered along some distance near the same boundary.

    So the real questions raised by the acc/snr issues include how many overlaid signals there are, which are real, and what generality each pattern may have – with the bottom line answer here that we have many questions, few answers.

  36. @EternalOptimist says:
    January 6, 2011 at 12:28 am

    Anything is possible says:
    January 5, 2011 at 8:52 pm

    The most striking thing about this article is the fact that abrupt climate chance is associated with the transitions from glacial maxima to inter-glacial conditions. By contrast, the transitions from inter-glacial to glacial maxima seem to occur gradually over tens of thousands of years, often in steps.

    This statement is flat out incorrect. Look up the “Younger-Dryas” interstadial. This was a VERY sudden return to ice age conditions. Its onset was almost immediate. Heck, it only lasted 1100 years before returning to the warming that had taken place. The timing was exactly at the end of the Pleistocene, at the very beginning of the Holocene, our current age – about 12,900 calendar years ago. It occurred right when the mammoths and other large N.A. mammals died off, at the end of the Clovis culture.

    BTW, they conveniently overlook that tie-in between the sudden onset of COLD and the extinction event. One of the theories of the extinctions has to do with climate change, but to be politically correct (or whatever) they choose to frame it as the exact opposite, a warming event that killed them off; this idea is complete rubbish.

    For those who have not heard of the Y-D impact event, I would invite you all to

  37. Some years ago, New Yorker had an article on the Greenland drilling and the data available to that point.
    There was a line chart going back about 140k yrs. The temp changes were substantial, larger variations sawtoothed with smaller on top, until about 14kya.
    At that time, the variations shrunk dramatically. There were still changes, but not nearly so large. It looked as if the graph line had gone through a knothole 14kya. Or as if you’d printed out a couple of dozen capital As on word at font 16, dropping to font 6.
    One of the scientists remarked that civilization could not have begun before 14kya due to the difficulty of coping with changes. Whether we can now was not addressed.

  38. Unfortunately none of this is relevant to the CAGW argument. These, being “natural” temperature variations, are not evidence for or against the CO2 “threat”. The study simply shows that something non-CO2 can flip the climate rapidly into or out of an ice age.

    The value of this report is in a comparison of what has happened and what AR$ says might/will happen in the near-future. Perhaps the CAGW crowd will say this proves the Earth’s climate to be very sensitive to ANY change. Should insolation or albedo be the actual cause of previous climactic sudden shifts, however, and we can get a handle on the magnitufe of the causes, then we will be able to show what small changes are require for the currently absurdly small temperature rise (since the 1980s) and look to find its signature.

  39. Wow, my last comment got clipped off. The last sentence was:

    For those who have not heard of the Y-D impact event, I would invite you all to http://www.CosmicTusk.com, where articles are posted as to a real catastrophe, not a made up one. What that catastrophe was is still being studied. One possibility has been proposed and skeptics are beating on it (sometimes with plenty of snark), and the proponents respond. It is a more civil discussion than CAGW, but not without its moments of viciousness.

  40. Onion: If there is a 5 meter sea level rise in the earth’s future, there is little anyone can do about it. Whether we want it or not is immaterial. Those who live along the coasts will have to adjust. As they have for thousands of years. It’s a problem people have dealt with before.

  41. Anything is possible says:
    January 5, 2011 at 8:52 pm

    The most striking thing about this article is the fact that abrupt climate chance is associated with the transitions from glacial maxima to inter-glacial conditions. By contrast, the transitions from inter-glacial to glacial maxima seem to occur gradually over tens of thousands of years, often in steps.

    This statement is flat out incorrect. Look up the “Younger-Dryas” interstadial. This was a VERY sudden return to ice age conditions. Its onset was almost immediate. Heck, it only lasted 1100 years before returning to the warming that had taken place. The timing was exactly at the end of the Pleistocene, at the very beginning of the Holocene, our current age – about 12,900 calendar years ago. It occurred right when the mammoths and other large N.A. mammals died off, at the end of the Clovis culture.

    _____________________________________________________________

    The Younger-Dryas episode was still part of the transition from the glacial maximum to the inter-glacial.

    One of the hypotheses as to its’ cause – postulated by Dawson,1992 – is that melting ice led to the formation of large glacial lakes on the North American continent, which were prevented from draining into the oceans by the remaining ice. As the melting continued the ice barrier was breached, causing a sudden, catastrophic release of cold, fresh water into the North Atlantic Ocean, causing a short-term regression of the climate in surrounding regions back into glacial mode.

    If this hypothesis is correct, it actually fits in quite neatly with my theory. It certainly doesn’t disprove it. In climate change, NOTHING is ever straightforward.

  42. Obviously we need to immediately extract every drop/crumb of fossil fuels from the arctic before they become covered with miles thick glaciers. We’ll need all that energy to cope with impending doom! I will not share the fate of some club weilding troglodite from the stone age due to a bunch of leftist ninnies who insist civilization needs to be driven by glorified pinwheels. :)

  43. Mike Haseler says: January 6, 2011 at 12:42 am

    It might not be what they think. If e.g. the temperature went through a warming period of perhaps several hundred years, the ice might melt repeatedly wiping from the record the whole period of gradual change from one climate type to another.

    My thought too.

    However… there are many other records in the geology etc that suggest catastrophic events at various times, and some of these could synchronize with Younger Dryas ice records.

  44. I would add to my previous comment that I am accepting the very premise of notable warming due to CO2 for the sake of argument only. I also contend that unless and until we accurately quantify human contribution of CO2 from what occurs naturally we are simply chasing our tails.

    Also, it isn’t up to me, or just about anyone else for that matter, to prove anything regarding the climate. That is what climate scientists and their enormous grants were supposed to do. So far, it can be demonstrated that virtually everything they have come up in support of human contribution to CO2 causing warming is either incorrect, incomplete or downright fraudulent. I heard one climate scientist (the warm variety) remark on CBC radio’ “Quirks and Quacks” this past Saturday that it is still unknown just how much CO2 humans are contributing to the overall amount. His statement was that he “feels mankind’ fingerprints” on it though, so we should just take his word for it. After all, he’s a climate scientist! Whatever. I now hold climate scientists in similar regard to trial attorneys. For a fee they will say and do anything: Sometimes for free. Not much hope in my ever taking his word it. I happen to believe in a legal principle that goes something like; if a witness under oath lies, even once, you may disregard everything they say as a lie. I submit that all those who claim to have proven AGW have lied, more than just once, and I choose not to believe anything they say.

    /rant

    I did enjoy the article Mr McClenny. Thanks.

  45. lots of dust …

    meteor strikes, volcanoes …

    nothing to do with climate change/chaos/disruption or whatever they are calling it now …

  46. @Anything is possible says:
    January 6, 2011 at 11:45 am

    One of the hypotheses as to its’ cause – postulated by Dawson,1992 – is that melting ice led to the formation of large glacial lakes on the North American continent, which were prevented from draining into the oceans by the remaining ice. As the melting continued the ice barrier was breached, causing a sudden, catastrophic release of cold, fresh water into the North Atlantic Ocean, causing a short-term regression of the climate in surrounding regions back into glacial mode.

    This one has been out there for some time and keeps being repeated, but Thomas V Lowell showed that the St Lawrence River was blocked by ice during the Younger-Dryas. [Revised Deglacial Chronology of the Laurentide Ice Sheet and Implications for Catastrophic Meltwater Discharge as Triggers for Abrupt Climate Change,” Eos Trans AGU 86 (52) Fall Meet. Supple., Abstract (2005): F1234″ — This from “Sudden Cold” by climatologist Rodney Chilton (2009)]

    Chilton goes on to say

    The slowly mounting body of evidence against the St. Lawrence route has recently led long-term advocate Wallace Broecker to state that “Although the ide of the Eastern North American route via the St. Lawrence was a seductive idea, it has now become very doubtful.” [Wallace S Broecker, “The Pre-YD Agassiz Flood,” Eos Trans AGU 86 (2005): Fall Meeting Supplement F1261]

    Chilton then adds

    A second study that involved a simulation of meltwater originating from the Laurentide Ice Sheet did not produce any appreciable meltwater during the entire 15,000 to 8,000 BP interval. [T.C. Moore (2000)]

    and

    The northern route at least appears to have suffered the same fate as the St. Lawrence in also being blocked by ice until well after the Younger-Dryas ended. [Thomas V. Lowell, ibid]

    As to the statement

    The Younger-Dryas episode was still part of the transition from the glacial maximum to the inter-glacial

    This is not the case at all. The Bølling-Allerød was the period when the overall summer temps climb by 8°C and 25°C in the winter, and it lasted a full 2,000 years, just prior to the Y-D, when the temps dropped within 100 years (probably less) by 15°C to 20°C in Europe and Greenland. There were shorter and milder fluctuations as the ice age ended about 20,000 years BP, but the Y-D was nothing like those little blips. It was a full-fledged return to ice age conditions for 1200 years, not part of some warming transition.

  47. Ken Hall says:
    January 6, 2011 at 5:09 am

    “Which shows that vast and rapid climate changes, (far in excess of the tiny 0.7 degrees rise of the 20th century, even IF it was that much), are NOT associated with and cannot possibly be caused, or driven, by CO2.”

    It doesn’t show that at all. What we see are lower rates of CO2 increase in the past. The current rate of CO2 rise is quite unprecedented in any of our records of past climate.

    “The current warming is not outside the normal noise of natural variability.”

    It doesn’t have to be. Even warming within natural variability can be dangerous.

  48. “starzmom says:
    January 6, 2011 at 10:44 am

    Onion: If there is a 5 meter sea level rise in the earth’s future, there is little anyone can do about it.”

    Unless we cause it.

    “Whether we want it or not is immaterial. Those who live along the coasts will have to adjust. As they have for thousands of years. It’s a problem people have dealt with before.”

    Not really. There’s never been a time in human history where we have had anything near a 6 billion size global civilization and had to deal with a large sea level rise. A large sea level rise in this situation would be greatly more catastrophic than if say it occurred while we had a hunter gatherer global population of a few hundred thousand (and no railways, airports, roads, power stations near sea level)

  49. “I heard one climate scientist (the warm variety) remark on CBC radio’ “Quirks and Quacks” this past Saturday that it is still unknown just how much CO2 humans are contributing to the overall amount.”

    Well it isn’t, we are contributing virtually all of the increase.

  50. “”””” Similar events, including local warmings as large as 16°C, occurred repeatedly during the slide into and climb out of the last ice age. “””””

    Well whoop de do ! So 16 deg C is 28.8 deg F.

    I can look at the SF Bay Area weekly weather predictions almost any week of the year and see Tmperature excursions predicted that are over 30 deg F, and sometime 40 deg F

    So 16 deg C “local” temperature changes, are so 20th century.

  51. Well then there is that famous 600 million year paleo-climate graph of CO2 and Temperature, that shows that since the pre-Cambrian, the global Temperature has never been higher that +22 deg C, and never lower than +12 deg C, so the spread is limited to 10 deg C total range.

    BUT !! take this in light of the fact that on any ordinary midsummer Northern day, the Total Local Temperature range of earth can be as much as 150 deg C or more, from lows of about -90 C in the Antarctic midnight, to +60 deg C for the hottest northern deserts. And remember that entire range can be found simultaneously. You can join those two max/min end points by a line; ANY line, going through anywhere else on earth, that you want to, and somewhere along that line will be found a Temperature of any value between the maximum and the minimum. So there is an infinity of such points with any temperature value between the extremes.

    So a 16 deg C local range ? Ho-hum; wake me when something actually happens.

    Credit Galileo Galilei for the proof of that assertion.

  52. Besides, if all that change happened in one year; that is just a local weather event; and not climate at all.

  53. William,

    My hat is off to you sir. Very well done, and very well summarized by Brian H.

    I have to admit that both “Climate Crash” and “Abrupt Climate Change” from the National Academies Press caught my attention years ago and had a heavy influence of my own sense of how to interpret our climate and its natural cycles. “Climate Crash” is a much easier read than “Abrupt Climate Change” and expresses the emotions of the scientists doing field research, at the time of their discovery. Before this point in time (1992?) it was well “known” that transitions into and out of periods of glaciation were “glacial”.

    I tried to make a point along these lines in a late comment I made to a recent post about the current cold weather being equated to AGW. This was about a week ago. In fact I used references to specific pages in “Abrupt Climate Change” to help make the point.

    In the case of that comment, the essential message was that these scientific field expeditions were real, undertaken and recorded. They led to scientific analysis and evaluation of the data and ultimately to scientifically based conclusions. In that comment, my point was that these scientists had reached these conclusions after collecting data from the field. That dat data in the form of ice cores is still available for analysis. The fact that “Abrupt Climate Change” was published by the National Academy is lost to today’s current crop of so-called climate scientists who are likely not even aware of this work. The term Abrupt Climate Change has a scientifically based meaning and now that term, “climate change”, is being used to hide the ruse of AGW… because the cold snow weather is caused by the climate change associated by AGW.

    How many of these current climate “scientists” would ever conceive, plan, seek funding for true field work like this, and spend months on the Greenland Ice fields to accomplish it? Better, perhaps, to blog about taking meaningless ice thickness measurements on flow ice during the arctic summer.

  54. Onion 2:46,

    You might benefit from some actual research on points like this:

    “Whether we want it or not is immaterial. Those who live along the coasts will have to adjust. As they have for thousands of years. It’s a problem people have dealt with before.”

    Not really. There’s never been a time in human history where we have had anything near a 6 billion size global civilization and had to deal with a large sea level rise. A large sea level rise in this situation would be greatly more catastrophic than if say it occurred while we had a hunter gatherer global population of a few hundred thousand (and no railways, airports, roads, power stations near sea level).
    —-
    The sea level rise you are concerned about already happened between roughly 10 and 7000 years ago when sea level stabilized after the northern hemisphere glaciers melted. Today’s changes in sea level have nothing in common with the 150 M sea level rise after the start of this interglacial period.

  55. Mike Haseler and LucySkywalker:

    You raise several interesting points. I have read widely on the YD, and what I can tell you is that there are a number of very compelling studies which suggest causative mechanisms, and just about as many challenging, and sometimes strengthening or weakening the case for most all. One interesting hypothesis is that it is the latest of the relatively unmuted D-O cycles. But what we really do know is that it happened And it may not have been unique. Evidence has been presented that YD events were present in several post-MPT terminations. But this gets progressively harder to discern the further one goes back, due to the constraints of the methods and proxies. There are also some interesting papers which propose that D-O oscillations are still present, but muted during the state-switch to the warm mode. All of it, including the scholarly thrust and parry, fascinating. If you think far enough outside the box, you may find that you have surrounded it. It lies within.

    I have yet to really get stuck-in to researching the details of the Greenland ice cores that tagged bedrock. From memory, my preliminary construct consists of this. The longest credible estimate that sticks to mind is that Greenland cores presently can take us back to 135kyrs or so. Those that have more solid data please chime in! Again from memory, I remember several studies of where shearing in the deepest cores were noted. But if it is true that, from the best present knowledge, no ice exists in Greenland older than the last interglacial, then that speaks volumes. It would seem that something happened during the Eemian to allow all previous ice to disappear. Assuming that this is correct, whatever the reason for no ice in Greenland pre MIS-5, then the most recent interglacial natural climate noise envelope has relevance.

    Just about as interesting is that Antarctic ice gets us back no further (again from memory) than the MPT. Prior to MIS-19 we do not find ice in Antarctica. I make no inference. Other than that we did, in fact, hit a climate tipping point. Whether or not we are still within the post-MPT climate envelope, on the brink to the switch to some other one, or if we will assert our own, remains to be seen.

  56. William – do I have it right: the purpose of this article was to demonstrate that, while it is well documented by your “wild climate ride” that ACC has occurred naturally in the past, there is no way we can differentiate S from N signals so as to be able to forecast in advance that it is about to happen again?

    Isn’t this just equivalent to saying that we can’t see into the future however much we’d like to? And wouldn’t the point be more forcefully made as to climate models and their forecasts?

  57. TimC:

    It is wildly more complex than that! But I do get your meanings…. First, how would we demonstrate it? Well…. It seems likely it will happen anyway. I remember calculating in 2005 that every non-purchase of a new car in the U.S. would be negated in something like 5 seconds in China alone. Back of the envelope style calc., you understand. Meaning the exclusion of developing nations from the eventual equation best not be ignored.

    But you do intimate something else which should not be ignored. The “See-Saw” effect. S-N, or vice versa. It is indeed rare for the hemispheres to be synchronous. All too often we see in the paleoclimate record the disparate responses of the hemispheres to significant climate changes.

    Although weather on the singular scale is easily seen to equate with climate change in the paleorecord, the leap required to substantiate such a climate state change vis-a-vis the present remains insubstantially questionable. So be ever thoughtful of both facts and predictions before leaping to a conclusion. It was in fact a LEAP that terminated the last interglacial, the cold Late Eemian Aridity Pulse which lasted 468 years and ended with a precipitous drop into the Wisconsin ice age. And yes, we were indeed there. We had been on the stage as our stone-age selves about the same length of time during that interglacial that our civilizations have been during this one.

  58. William M;
    That’s a fascinating observation about the human presence in the previous interglacial. Given that there was supposedly only Paleolithic tech available at the start of this one, what made the difference in development pattern? Why were there no major civilizations in the previous interglacial? Is it, in fact, certain that there were none?

    And, of course, the phrase “about the same length of time” covers a multitude of possibilities. A few thousand years here and there make a big difference.

  59. P.S. to above;
    of course, I realize that there may not have been an adequately “modern” human extant to take the aurochs by the horns.

  60. William – just to come back quickly one time, while I also find the history (and related human development) an interesting tale, your Summing Up raised a specific question on which I think I summarised Brian H’s reply fairly – that attribution of current or upcoming [future] ACC event is impossible [that we can’t see into the future].

    So, while ACC events are all very interesting at an academic level, we can’t predict them: for the purposes of the present AGW debate we can only say that ACC events have occurred in unpredictable circumstances. Even if we see a number of seeming precursor events to an ACC, we still can’t say more than this.

    I personally think that regular events, such as the regular cycle of ~100ky glaciations in the recent quaternary, are more relevant to the AGW debate. One can seek to draw conclusions from them which are probably valid in the debate: not least (with a lawyerly hat on) that presumption of continuance is likely to apply, absent some event of astronomical scale.

    Thanks for the interesting article, all the same.

  61. William McClenney says:
    January 6, 2011 at 7:59 pm

    “Just about as interesting is that Antarctic ice gets us back no further (again from memory) than the MPT. Prior to MIS-19 we do not find ice in Antarctica. I make no inference. Other than that we did, in fact, hit a climate tipping point. Whether or not we are still within the post-MPT climate envelope, on the brink to the switch to some other one, or if we will assert our own, remains to be seen.”

    I have to wonder how much continental drift had to due with the tipping point at the MPT. Antarctica wasn’t as centered on the south pole a million years ago as it is now. Antarctica’s capacity to keep water out of the global hydrological cycle has gradually increased as it has drifted further south, onto the pole. Also, a million years ago the Pacific Ocean was a bit larger, the Atlantic was a bit smaller, and the arctic ocean wasn’t quite as encircled by land masses as it is now.

    The most obvious changes to me relate to the hydrological cycle. At the MPT, glacial cycles switched from 41kyr intervals to 100kyr intervals, in which our warm periods became less frequent. Locking up water flow at the poles has a twofold effect – preventing that water from gathering heat in the tropics, and increasing the albedo of the planet (when that water is frozen, instead of in an ocean). And with a different shape/size to the oceans, the PDO an NAO would have been the different.

  62. TimC;
    It’s not just “predicting the future” which un-diagnosed noise obscures; it also makes deciphering the past and present very iffy. If you don’t know causality, then statistics is just betting on “same old, same old”.

    Of course, it is possible, even likely, that the entangled causalities (if that’s a word!) may not be susceptible to sufficient isolation to ever permit such understanding. In any case, it’s hard to see how you would ever know that the cause-effect sequence you postulate actually works independently–that it’s not contingent or susceptible to large non-linear excursions under the influence of others.

    That’s part of what I gather from descriptions of the climate as a “field”, requiring a full solution, not subject to reductionist unravelling.

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