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What triggers ice ages?

Filed under: — rasmus @ 16 February 2007 - (Português) (Türkçe) (Français)

by Rasmus Benestad, with contributions from Caspar & Eric

In a recent article in Climatic Change, D.G. Martinson and W.C. Pitman III discuss a new hypothesis explaining how the climate could change abruptly between ice ages and inter-glacial (warm) periods. They argue that the changes in Earth’s orbit around the Sun in isolation is not sufficient to explain the estimated high rate of change, and that there must be an amplifying feedback process kicking in. The necessity for a feedback is not new, as the Swedish Nobel Prize winner (Chemistry), Svante Arrhenius, suggested already in 1896 that CO2 could act as an amplification mechanism. In addition, there is the albedo feedback, where the amount of solar radiation that is reflected back into space, scales with the area of the ice- and snow-cover. And are clouds as well as other aspects playing a role.

Orbital forcing Martinson & Pitman III’s hypothesis states that the fresh water input works in concert with the Milankovitch cycle and the albedo feedback. They conclude that ‘major’ terminations can only follow from glacial build-up of sufficient magnitude to isolate the Arctic, inhibiting the inflow of fresh water to the point that salinity buildup in the surface layer from slow but continuous growth of sea-ice, causes overturn of the Arctic (through the effect on the atmospheric circulation and the ocean currents). The vertical overturning brings warmer water up from below, setting conditions that are more favourable for ice metling. Salinity plays a role too, but the hypothesis does not mention variations in the greenhouse gases (GHGs). A few questions: Did Martinson and Pitman III forget this last point? Or did the GHGs only represent a minor contribution? And, could not changes in GHGs explain much of the variability? On the other hand, it sounds plausible that changes in salinity and fresh water input may affect the sea-ice formation and the deep convection. However, so far, the hypothesis proposed by Martinson and Pitman III is merely a speculation, and we are waiting to see if the hypothesis can be tested through numerical model experiments (which would require higher resolution sea-ice and ocean models than used in todays global climate models). It would be interesting to carry out experiments to assess the significance of the fresh water only, GHGs, and the combined effect.

One reaction to the Martison and Pittman paper is: Where is the calculation of energy? Greenhouse gases only contribute a couple of W/m2, vs. the seasonal Milankovich forcing of >40. For this new idea to have merit, it had better have heat fluxes at least on par with the radiative forcing from CO2. Previous modeling studies find that GHG make up roughly 50% of the total LGM to present temperature response (see e.g. Broccoli & Manabe), the other part being albedo etc that respond to the seasonal cycle of irradiance. It is tricky to completely isolate the individual causes because changes in GHG may produce altered cloud and sea ice distribution. But roughly speaking, if you do an LGM run and only reduce sea level, put in the ice sheets, change the vegetation, add some dust (though that one is still rough), then you get about 50% the way you want to go. Change the GHG concentrations and you get close. This is more or less what Manabe and Stouffer showed 15 years ago. The question is do we need anything else, really, and does that ‘anything else’ pack sufficient punch.

139 Responses to “What triggers ice ages?”

  1. 51
    Steve Reynolds says:

    Re 49:
    >There is an important role to be played by climate scientists in educating the piblic and policymakers about the science, a role that is exemplified by this blog. It’s rather less constructive for climate scientists to spend their time engaging in endless rounds of nit-picking with denialists who are in the end unconvincable.

    For those of us with an open mind about the issues, answering the ‘nit-picking’ questions at least once is important as well.

    In looking at the data (for the US), there seems to be a very systematic pattern to the adjustments. Temperatures are reduced from 1920 to 1960, and increased from 1980 to 2000. Why do the adjustments look so systematic? The only adjustment that would obviously have a long term dependence on time (urban) should go in the other direction (and does in Hansen et al, 2001, but is very small).

  2. 52
    William Astley says:

    In reply to “With these monumental changes in the shielding effect of the Earth’s magnetic field, you’d expect to see fairly massive climate consequences if the GCR crowd are right. After all, the implied changes in GCR flux are huge compared to what is expected from the gentle modulation of the Earth’s magnetic field arising from recent solar activity changes (not that there’s any trend in those that would explain recent warming).”

    The hypothesized physical reason why there were not wide swings in climate (the planet was close to the glacial maximum, at the time of the Laschamp excursion of course. i.e. very, very cold) during the Laschamp excursion is: Although GCR does increase as the geomagnetic field decreases, there is a saturation point where additional ions created by GCR does not increase cloud cover. The concept of asymptotic approach to a level of GCR where further increases has less and less affect on cloud cover, is the same as with CO2 increases. The question for both forcing functions, CO2 and the set of cloud modulation forcing mechanisms is: What is the correct parameterization?

    As noted, one of the unanswered questions is: What caused the observed 1993 to 2001 reduction in planetary cloud cover? The hypothesized mechanism is electroscavenging which is due to changes to the global electric circuit. Changes to the global electric current can and do occur, initiated by solar changes, independent to changes to GCR.

    It has been stated in this forum that the increase in global temperature in the last decade of the 20th century does not correlate to GCR changes, which is correct. There is, however, no mention that the increase in global temperature does correlate with the observed reduction in planetary cloud cover, 1993 to 2001. In addition, the cloud cover decrease, 1993 to 2001 is restricted to regional areas, which matches the mechanism that Tinsley and Yu predicted, as Palle noted in his paper. For example, there is a reduction in clouds over the Atlantic Ocean at latitudes where the global circuit change is greatest. The atmosphere above the ocean is ion poor as compared to the atmosphere over the continents, as there is natural radiation from the continental crust. There is not natural radiation from the ocean.

    I believe there was been no discussion of electroscavenging in this forum. The retort is always the same, “The 20th century temperature increase, does not correlate with GCR changes”. The electroscavenging hypothesis does explain the reduction in cloud cover. Electroscavenging removes the ions that GCR produces, which makes it appear that changes in cloud cover no longer correlates with the solar cycle modulation of GCR.

    Science is not defending a position, but rather solving puzzles. This is a rare time where there are multiple crises in interrelated scientific areas: the geomagnetic field, the solar cycle, GCR/Global Electric Circuit atmospheric science, and the climatic cycles. The issues are with first order changes: What causes the termination and initiation of the glacial cycles; What causes changes in clouds, what causes the abrupt temperature changes; What is causing changes in the geomagnetic field; and What is the relative warming affect of enhanced CO2?

    [Response: This is just science fiction. You can spin all the word tales you want, but until you come up with a set of equations saying why the cloud cover changes should have been less in glacial times, or why the climate should have been less sensitive to cloud cover at the time, you might as well be talking about space aliens blocking the sunlight. You talk a good tale, Mr. Astley, but science is a high stakes game, and you’ve got to pony up some real equations if you want to play. –raypierre]

  3. 53
    Hank Roberts says:

    Reading the published work, they thought they had a correlation picking a few areas of the planet; when they got in enough data to study it globally, they didn’t find an effect:

    ” … the geographical variation of the correlation between low cloud and predicted ionization level from cosmic rays at an altitude of 2 km. When analysed globally, we find that the correlations do not correspond to the latitude variation of cosmic ray flux and they are not field significant. ….

    Then they went back to the areas where they said they’d found a correlation, and did a what-if:

    … We use a simple model to calculate the climatic impact should the correlation be confirmed. We show that, under the most favorable conditions, a reduction in low cloud cover since the late 19th century, combined with the direct forcing by solar irradiance can explain a significant part of the global warming over the past century, but not all. However, this computation assumes that there is no feedback or changes in cloud at other levels.”

    Other papers are along the same line, they don’t have a mechanism yet and are looking for correlations, near as I can tell.

  4. 54
    Rob Negrini says:

    Re: 45. A credit where credit is due thing. Although I’m sure Lloyd Keigwin did enough to deserve to be put on the paper, it is much more apt to call the Laschamp Excursion study “Steve Lund’s paper”. He did the bulk of the work and is responsible for characterizing the magnetic field behavior. Picky, I know, but had to be said.

    [Response: Not at all picky. I should have called it Lund’s paper, and it was just sloppy of me to call it Keigwin’s. I have a habit of remembering papers by the author I know best, not by the first author. A lot of people seem to do the same, the most famous case of which is the original Nuclear Winter paper, which a lot of people think of as “et al and Sagan.” –raypierre]

    Also, why is the GCR thing still in play? Anyone who still believes this to be an important hypothesis need only to graph the Climax neutron incidence data for the past 50 years against global temperature. There’s simply no long term trend in the GCR to correlate with the increase in temperature. Furthermore, the higher frequency trends in the GCR (i.e., sunspot related oscillations), which have MUCH higher amplitude than any remotely imagined long-term trends, don’t seem to have an effect that rises above the background noise in the temperature record. Again, why is anyone taking this seriously?

  5. 55
    DaveScot says:

    I was browsing the NASA interactive satellite temperature data for the troposphere which stretches from 1979 to 2003. It has a global map that’s colored in shades of red for heating and blue for cooling. Flipping through the time sequence it’s obvious that almost all the heating anomalies are in the snow covered far north. South of Canada down to Antarctica isn’t really heating at all. Moreover, there’s a graph of the average temperature anomalies of all areas (below the world map) and that shows that the net of heating and cooling is just about zero. I was wondering what could account for this pattern of heating and cooling and it occured to me that if the albedo of the snow cover in the far north was declining that would do it. So I looked around and dug up a study of snow albedo that appeared in the Journal of Atmospheric Sciences, Volume 37, August 1980 which confirmed that carbon soot from manmade sources (including forest fires) migrates thousands of miles and accumulates on permanent snow cover causing melting and temperature increases. The antarctic is relatively free of soot buildup but the arctic has been well contaminated.

    This explains the heating (and lack of heating) patterns quite well. How does CO2 greenhouse heating explain these patterns and why is the global average temperature not really increasing?

    [Response: Congratulations, you’ve just discovered “polar amplification.” This pattern is common to most means of heating up the planet, including CO2, and is not prima facie evidence for soot controlling everything. A superficial look at the patterns can make it look like all the warming is in the Arctic, since that is indeed where the effect is strongest so far. However, as the recent National Academy report pointed out at great length, a careful study of the most careful satellite retrievals indicates consistency between the satellites and the surface network regarding the warming — and that means that there is indeed warming in the midlatitudes and tropics, not just in the Arctic. I’ll leave it to Gavin to comment on the status of the soot-albedo issue. Hansen made some pioneering attempts to estimate the magnitude of these effects, but like most pioneering attempts they’re not the last word on the subject.

    By the way, for further illumination readers should click on the DaveScot’s name below the comment, to follow the link to where he has posted his take on the satellite trends (a classic case of jumping to the desired conclusion based on a superficial analysis). The link takes you to Dembski’s Intelligent Design web site. The common cause being made between global warming skeptics and Intelligent Designers, both of which dress up their arguments with the exterior trappinggs of science, is — as Mr. Spock would say — “fascinating.” –raypierre]

  6. 56
    Lynn Vincentnathan says:

    So, when would we have been due for another ice age, assuming there had been not AGW? I can’t tell by the graph very well, but it looks like it would have been soon in geological terms (which might be hundreds, if not thousands of years from now).

    Is it possible that our current AGW, if it goes on without drastic mitigation, could push us out of this glacial-interglacial cycle into something a lot hotter that stays that way a lot longer than most past times (except the 55 & 251 mya events)?

  7. 57
    David B. Benson says:

    Re #55: Lynn Vindentnathan — My understanding is that without AGW the climate should have been very slightly cooling and doing so for the next 50,000 years. At that time it might be cool enough for an ice age to start. The next opportunity is in another 50,000 years or so.

  8. 58
    Blair Dowden says:

    Re #56: I have seen estimates from ten thousand to fifty thousand years before the next ice age begins. So the idea that global warming saved us from the ice age does not hold water (or ice).

    Your second question is more interesting. Three degrees of warming takes us back about three million years, to an era known as the Pliocene. This was a much more stable climate that lasted a long time. The Earth seemed quite “happy” with this climate, although happiness included sea levels 25 to 35 meters higher than today.

    The real question is what caused the increasingly severe ice ages in the first place? I have not seen a clear answer to that. I suspect that after the greenhouse pulse stopped, the climate would return to near normal (ie. Holocene interglacial) in a few hundred years. But not quite normal because carbon dioxide levels take a long time to decay to nothing. So global warming might actually delay the next ice age, but only ten thousand years from now.

    [Response: We’ve just come out of one of the big every-100KYr glaciations, and the normal course of events is to build up to another biggy through a series of small, short glaciations over the next 100KYr. In the normal course of events, the first try at an ice age would be due sometime in the next 20,000 years but I myself wouldn’t try to pin it down more than that. One of the most interesting attempts so far to say what global warming might do to the glacial cycle is in the paper (pdf) by Archer and Ganopolski that appeared in the AGU journal GGG. I’ll leave it to David to say whether that has been followed up by more detailed GCM work. –raypierre]

  9. 59
    dhogaza says:

    Real Climate regulars will be glad to learn that in a few short minutes, DaveScot has overturned decades of climate research:

    Pretty incredible. I take one look at the real satellite temperature data instead of the pencil whipped crap that�s foisted upon the public and in a few hours figure out the real cause of global warming and then find the studies that confirm my suspicions. Gawd I�m good. We�ve been lied to. C02 greenhouse effect is a lame duck. All politics and no science.

    He did this after lunch. Before lunch, he was busy overturning 150 years of evolutionary biology.

  10. 60
    Zeke Hausfather says:

    For the RC folks:

    I was at a talk by Jim Hansen awhile back, where he argued that anthropogenic warming has brought us to a point where future ice ages are effectively impossible, provided that atmospheric levels of GHGs remain at or above their current levels. His point, as far as I recall it, was that the radiative forcing of anthropogenic GHGs is already greater than that of the Milankovich cycles that are thought to trigger ice ages. I’m curious about your take on this.

    [Response: In the annual average, Milankovich only gives you a around 5 W/m^2. Whereas athrogopogenic CO2 and other human-enhanced GHGs are now about 2.5 W/m^2 above their preindustrial values. We will certaintly push over 5 before the start coming down again. So Hansen is right, basically. On the other hand, it is the seasonal forcing in summer that really determines whether glaciers can survive the summer, and GHGs are not going to approach the magnitude of seasonal Milankovich forcing. So I would not cavalierly state that future glaciations are impossible. –eric]

  11. 61
    David B. Benson says:

    Raypierre — Thank you for your comments at #58 by Blair Dowden. Unfortunately, the link to the paper by Archer & Ganopolski fails to function correctly for me…

    [Response:Fixed. –raypierre]

  12. 62
    Hank Roberts says:

    On Gaia, evolutionary biology overturns _you_.

    Can’t hardly do climate change research without considering the ‘cold case’ from geological time — I guess climate change research isn’t possible without “Darwinism” eh?

    And if we didn’t look at the geological history, if all we could look at is the current few centuries of more reliable records — who could know anything useful from just that much?

    Has anyone illustrated what’s known about climate forcings for various points in geologic time, the same way the IPCC does forcings nowadays.

    snips and cites:

    “Biostratigraphy is the differentiation of rock units based upon the fossils which they contain. Paleoenvironmental analysis is the interpretation of the depositional environment ….

    200,000 years ago
    ” …. Calcareous nannofossils are … made of calcium carbonate. Nannofossils first appeared during the Mesozoic Era and have persisted and evolved through time. … One extant group that produces “nannofossils” is the Coccolithophorans, planktonic golden-brown algae that are very abundant in the world’s oceans. The calcareous plates accumulate on the ocean floor, become buried beneath later layers, and are preserved as nannofossils. Some chalks, such as those comprising the White Cliffs of Dover, are composed almost entirely of nannofossils. …. … planktonic mode of life and the tremendous abundance of calcareous nannofossils makes them very useful tools for biostratigraphy.”

    Nice drawings there, cited to unpublished training manuals, worth a look.

    and a hat tip to British Petroleum for data; anyone know if this kind of imagery is online?

    “paleoshorelines through the 240 million years of the Mesozoic and Cenozoic are presented within this atlas. Thirty-one maps, generally corresponding to stratigraphic stages, provide a snapshot of the continents and their shorelines at approximately 8 million year intervals.”

  13. 63
    Glen Fergus says:

    Re #34 OT: “Great Andean Glacier Will Melt to Nothing by 2012”

    Thompson’s suggestion is that the main Quelccaya outlet glacier, Qori Kalis, will disappear by 2012, not that the whole ice cap will. That has a way to go yet. See – Qori Kalis is the little valley glacier left of centre in the sat pic. I should find a more recent image to add to the animation.

  14. 64
    tamino says:

    Re: response to #60

    In the annual average, Milankovich only gives you a around 5 W/m^2.

    Isn’t that the figure for latitude 65o? Isn’t the global annual average from Milankovitch generally no more than about 0.4 W/m^2 insolation?

  15. 65
    Regina says:

    What triggers “obscuring” of an issue that should concern every living soul on this planet? Privileged rhetoric for academics only?

  16. 66
    William Astley says:

    In reply to comment 41: What is the evidence for rapid geomagnetic field changes?

    Attached are two links to papers:

    From Acton’s paper that discusses the Africian Afar anomaly: “One lava flow has recorded both of the antipodal transitional components, with the two components residing in magnetic minerals with unblocking temperature above and below approx. 500C,… Hence the configuration of the geomagnetic field, appears to have jumped nearly instantaneous from a north-hemisphere transitional state to a south-hemisphere one during this normal-to-reverse polarity transition.”

    From Coe et al’s 2002 paper that discusses the Oregon anomaly: “Paleomagnetic results from lava flow recording a geomagnetic polarity reversal at Steens Mountain, Oregon suggest the occurrence of brief episodes of astonishing rapid field changes of six degrees per day. The evidence is large, systematic variations… in a single flow… most simply explained by the hypothesis that the field has changed direction as the flow cooled.”

  17. 67
    Hank Roberts says:

    How about this one?
    “… (All researchers agree that the very, very rapid field changes could not possibly be due to changes in the earth’s core. If the problematic data is correct, the earth’s magnetic field is not generated in the core.)”

  18. 68
    Blair Dowden says:

    Re: Ray’s response to #58: When you refer me to a paper, I read it and have questions.

    First, does this page correctly represent the carbon dioxide absorption rate?

    Do the three scenarios in the Archer paper represent carbon dioxide emissions from the start of the industrial era (ie. 300 Gt is what we already have), or from now?

    I don’t understand why the present interglacial is supposed to last so much longer than the others (without human input). Is there another cycle longer than the 400 Ky eccentricity cycle?

    To answer the original question, it appears that emissions of 1000 Gt (which is not unreasonable) could delay the next ice age by 50,000 years, contrary to what I said.

  19. 69
    Lynn Vincentnathan says:

    Looking at the stages of glaciation line at the bottom, I’m thinking that the cooling downswing is gradual & hitting plateaus, while the warming upswing is rather sharp & strickly increasing.

    It seems that the positive warming feedbacks are somewhat stronger than the positive cooling feedbacks — struggling against them, if you will. It may be that both cooling & warming may trigger methane clathrate release from the oceans (which eventually breaks down into CO2). These are at various sea levels, apparently some closer to sea level than previously thought, according to a recent study.

    I’m imagining this scenario (which may be wrong): As it cools the sea level goes down with ice going into glaciers, and this exposes the clathrates at various levels, which melt during warm summer days, and go into the atmosphere, cause warming, or counterbalance or slow the cooling. Other geological cataclysms, such as landslides, are also releasing these.

    Then during the warming, even though the sea is rising, it is also warming, releasing these clathrates, reinforcing the other warming mechanisms. But it never quite warms deep enough to melt all of it, though underwater landslides, earthquakes, or volcanoes could release these deeper/colder deposits now and then.

    Which brings us to now. Here we are lickity split (in geological time) releasing carbon into the atmosphere, causing warming to perhaps go above the usual thermal maximums, and even though the sea is rising, it is also warming rapidly, so we could expect more methane to be released as we heat up.

    Does the atmospheric carbon chart follow this slow nonstrictly cooling and quicker strictly warming patterns, as least for some of the events (of course, other mechanisms would be at play, since they’re not staying constant)?

  20. 70
    Lynn Vincentnathan says:

    My thinking about GCR & magnetic fields is this: we can’t really do much about them. So, if they do have an effect on warming, then we need to focus even more strongly on what is under our control, and that is our own GHG emissions. What if all these warming factors were to converge – solar, GCR, magnetic fields, volcanos, AND our high GHG emissions — we’d really be in hot water. So we must do all we can to reduce our GHG as quickly as possible. We human might just be the straw that triggers the greatest mass extinction ever.

  21. 71
    tamino says:

    Re: #69

    I don’t think it’s the greater rapidity of warming feedbacks over cooling feedbacks that causes the skewness of glacial patterns. It’s more likely due to the fact that building an ice sheet is a slow process of steady accumulation, a thermodynamic process, while wasting an ice sheet can happen rapidly, as a mechanical process. Think of an iceberg calving off a glacier into the sea; in a few seconds, the glacier loses tons of ice. But the creation of that ice happens one snowflake at a time.

  22. 72
    Leif G Liland says:

    Could this fresh water inflow and change in salinity also be the force behind the 3500 years cycle shown here:
    and how much of the ongoing warming at high latitudes could be caused by this natural cycle?

  23. 73
    Ray Ladbury says:

    My take on the GCR forcing mechanism is that it is an interesting hypothesis that should be investigated further. However, given that we already have even larger variations on an 11 year timescale, and that the CR fluxes in the space era have not changed, it’s hard to credit the hypothesis.
    The speculations about the geomagnetic field are in my opinion rather wild. If you look at the way a field flip occurs, initially you start seeing more of the energy going into the higher multipoles. These configurations are not stable and oscillate rapidly. Perhaps these flows took place during the few thousand years of a flip, and the anomalies are due to rapid local variations. To hypothesize the the geomagnetic field might originate somewhere other than the core is well beyond speculative.
    I think what we see here is the tendency of humans to try to explain the unexplained in terms of the unexplained (or at least the not-well-understood). Humans seem to like even better to explain things in terms of SEP (somebody-else’s-problem) or best of all NP (Nobody’s problem i.e. nobody can do anything so lets all sit in the deckchairs on the Titanic and pop a cold one rather than rearranging them).

  24. 74
    pete best says:

    Off Topic but now the Arctic is at 390 ppm.

    2 ppm annual increase.

  25. 75
    Margo says:

    [[Response: This is just science fiction. You can spin all the word tales you want, but until you come up with a set of equations saying why the cloud cover changes should have been less in glacial times, or why the climate should have been less sensitive to cloud cover at the time, you might as well be talking about space aliens blocking the sunlight. You talk a good tale, Mr. Astley, but science is a high stakes game, and you’ve got to pony up some real equations if you want to play. –raypierre]]

    It’s fair enough to ask for equations to back up speculative arguments and to suggest that without them one might as well be suggesting space aliens are involved.

    I had the same reaction when I read the equationless article What does the lag of CO2 behind temperature in ice cores tell us about global warming? published at realclimate in 2004.

    I clicked the link to to find the equations, but that link is dead. I found this, which contains no equations showing how this positive feedback mechanism works in practice. So, is there a paper showing a model for the evolution of both Temperature and CO2 with time based on any known physical processes? Does solution of these equations suggest an 800 year lag in CO2? Does the solution explain cycles in temperature etc.?

    I’ve been wondering because as it stands, the RC article is interesting, but it would be nice to see it firmed up and quantified so the speculative idea could be tested.

  26. 76
    Steve Bloom says:

    Re #62: That joke is great, Hank. It’s the funniest thing Yakov Smirnov never said. :)

    Re #75: But why risk sullying the purity of your denialist views?

    Seriously, Margo, if you think there’s anything to William Astley’s stuff, I believe you have a blog you can devote to exploring it in detail. You might start with taking the obvious step of backing up to the main pub page at the link you noted and looking at all those other papers. The try Google Scholar and make use of your fine university library. If you have any remaining questions, try emailing Jeff Severinghaus. Good luck with that.

    In the meantime, if the RC authors think an idea amounts to flat-earthism, IMHO spending any time on it beyond a brief summary refutation is contrary ro the purposes of this blog.

  27. 77
    Margo says:

    Re 76:
    How is that any sort of answer to my question? Why are you suggesting I am thinking of anything to do with William Astley?

    I asked whether or not there is a complete theory describing the speculative feedback mechanism advanced here at Real Climate. Presumably, since the whole team at RC wrote the post proposing the existance of a positive feedback between T and CO2, and raypierre is holding a high standard against mere speculation about physical mechanisms, someone here at Real Climate has seen such a mathematical model. If they have should be able to point me to they paper.

    As it happens, if such a theory exists, it would touch on the topic or what triggers the ice ages– so I suspect others might like to see it.

    (It also happens that if the whole team doesn’t know of such a paper describing such a model, then that might suggest that raypierre doesn’t really think these mathematical models really need to exist to before one can speculate about phenomenology. It won’t make the previous commenters speculation correct–but it would suggest that little space alien comment was a bit harsh. )

    For the record Steve, it may come as a surprise to you, but I am not a denialist. I think we’ve increased the amount of CO2 in the atmosphere and I think it’s likely resulted in some increase in global temperature.

    Also, for what it’s worth, I’m under the impression that the authors of RC actually like to provide references and explanations for their theories when they have them. However, if you are correct and they don’t like to do so, I’m sure they can tell me that themselves.

    So, in the hope of getting what I most want, let me close by saying:

    If the team or raypierre, or their guest author is familiar with a paper that contains an actual full mathematical model describing the effect of a positive feedback mechanism between CO2 and T discussed in their previous article, I’d like to read it. Honestly.

  28. 78
    Hank Roberts says:

    Er. You’re asking for a “complete theory” and “an actual full mathematical model” — can you say what papers you would say don’t meet your standards, of the major ones?

    Have you read this one? (I’ve seen only this press release for it)

    “… 26 May [2006] in Geophysical Research Letters, Marten Scheffer of Wageningen University in the Netherlands and colleagues at the Potsdam Institute for Climate Impact Research in Germany and the Centre for Ecology and Hydrology in the United Kingdom use newly acquired ancient climate data to quantify the two-way phenomenon by which greenhouse gases not only contribute to higher temperatures, but are themselves increased by the higher temperatures. This higher concentration leads to still higher temperatures, in what scientists call a positive feedback loop.”

    (I don’t know if the commenters here have mentioned it; not finding it with the search tool)

  29. 79
    Margo says:

    Hank Roberts[[Er. You’re asking for a “complete theory” and “an actual full mathematical model” — can you say what papers you would say don’t meet your standards, of the major ones?]]

    I wasn’t saying I knew of papers that don’t meet standards. I was saying that the paper cited in your real climate article What does the lag of CO2 behind temperature in ice cores tell us about global warming? speculated about the existence of a positive feedback but cited zero articles containing anything that could remotely be called a mathematical model to describe any sort of positive feedback loop. -That’s why I was asking for a citation. (Like Raypierrs, I happen to like these models– which is why I said it’s reasonable to ask for them. That’s why I wished the earlier RC post had cited a model — it would make the idea more concrete and testable. )

    So far, no one had suggested a paper containing a model. The only person who responded was Steve Bloom, who seemed to think I should not be asking for any such paper. (Or something.)

    The link you gave was for the press release– but I think I found the pre-press version here:
    Is this the correct paper? This does contain an actual mathematical model. Now I can print it out and read it to see what I think of it. (And as a bonus, Steve Bloom can read it too! )

    Thanks! :)
    Oh– if there are other papers, that would be of interest too.

  30. 80
    Steve Bloom says:

    Re #77: Regarding the Astley reference, it sounded on first reading as if you were defending him. On a more careful reading I see that what you were really doing was snarkily equating Ray with him. Whatever.

    Regarding your particular brand of denialism, it appears clear enough from your blog and posting record that you’re only interested in learning enough about climate science to go on the attack against it. Of course you’re free to refer to yourself using any term you like.

    On the substance, I was curious enough about this issue to be willing to do some of your research for you. I couldn’t find public-access copies of any of the papers, but the short answer seems to be that the equations are built into specialized models (not GCMs) that are used to look at ice age behavior. This student paper from 2005 has a nice narrative of the history of these modeling efforts and then discusses in some detail the plans for improving the McGill one, although I’m sure plenty has happened in the intervening two years. It names many if not most of the models involved, so it should be easy to go find current information on them and extract the relevant algorithms. As you’ve recently been spending time trying to pick apart the GISS GCM, that shouldn’t be too tall of an order for you.

    BTW, you use the phrase “speculative feedback,” but the existence of the feedback itself is not a matter of speculation at all. The exact mechanism for the feedback is not settled (call that speculative if you want), although many of its parameters have been determined.

    Be sure to give my regards to John A.

  31. 81
    Steve Bloom says:

    Re #78/9: The paper Hank linked is on the strength of the amplification effect of anthropogenic GHG emissions at the present time, which is rather different issue from the past lagged relationship between glaciations and CO2.

  32. 82
    Margo says:

    Re 81 Steve Bloom. The paper Hank suggested does not contain a positive feed back model of the sort that would explain why the 800 years lag in CO2 in ice cores. As it happens, the student paper you cite contains no such model. In fact, it doesn’t even contain a single equation — which would be a rather minimal requirement for a paper describing a mathematical model.

    But since you ask me what I am looking, I shouldn’t be surprised the paper you suggested doesn’t provide a mathematical model. Here’s what I am looking for:

    A specific model that would support thespecific argument in What does the lag of CO2 behind temperature in ice cores tell us about global warming? written by the RC team. The argument they advanced in their article includes the claim that the 800 year lag in CO2 can be explained by a positive feedback mechanism. That’s a rather precise claim–not only is there a positive feedback, but it’s consistent with the 800 year lag in CO2, and the whole ball of wax explains the magnitude of the changes in temperature associated with ice ages and interglacials.

    A reference containing such a model should be rather easy for the team to supply if— as raypierre’s response to Astley suggests– the RC team members really don’t accept speculation until after they have read and accepted some sort of mathematical model to explain the speculation.

    Of course if there is no such paper, or even if it exists, but the RC authors are unaware of the paper, then with regard to this specific theory explaining the meaning of the ice cores, maybe that would suggest the RC authors, including raypierre don’t actually believe these sorts of models are always required before one can accept a speculative argument.

    (For the record, I happen to think speculative arguments do have a legitimate place in science. Mathematical models are more concrete, and so I like to see to see them. If the RC team knows of a mathematical model to explain the argument advanced in ” What does the lag of CO2 behind temperature in ice cores tell us about global warming?“, I really would like to see it.)

    [Response: I don’t really know what you are looking for since I don’t know that anyone has ever claimed to have a pure mathematical basis for the changes in oceanography and biology that control the CO2 level. However, there are lots of reasonable heuristic models that demonstrate the reasonableness of the idea – Didier Pallaird for instance (Paillard, 1998; 2001, and references therein.). It should be clearly stated that a full understanding of ice age carbon dioxide cycles is still elusive, but conceptually, there is absolutely nothing difficult about a lags in the system on the order of the ocean overturning timescale -on the contrary it is to be expected. -gavin]

  33. 83
    Reid says:

    Tamino said: “The FFT is a poor choice, because is requires the data to be evenly spaced in time (which often it is not), and requires the number of data points to be a power of 2 (which it almost never is).”

    The number of data points does not have to be a power of 2. Modern FFT algorithms automatically break up the time series into a subset of primes. It goes faster as a power of two, though, and this can be effected simply by padding the series with zeros up to the power of two. Zero padding can also be used to increase the resolution of the PSD. See the classic text by Oppenheim and Schafer (the latter one of my old profs).

    Unfortunately, though, the FFT does require the data to be evenly spaced in order to take advantage of the symmetries of the Fourier series.

  34. 84

    Reid, thats true that you don’t neccessarily need a factor of 2. Padding the series with zeres is essentially the same as interpolating the time series, and if you’re going to interpolate it anyway you might as well make it a power of 2 AND give it even spacing. Tamino’s use of the DCFT was appropriate though, and makes the issue moot. DCFT takes a lot more compute power but in this era of Core 2 Duo laptops and matlab licenses, who cares? :) (I’ve got an old pre-Yonah “Dothan” Pentium M thinkpad which gets the job done just fine).

    I still think that the frequency graphs are more intriguing than the original time series (I work in MRI physics, so I have a bias towards the frequency domain). If you’re trying to establish a case for the complexity of inputs to the warming cycles, then overlaying the various peaks on each other on a single colored graph would be immensely useful for a layman.

  35. 85
    tamino says:

    Re: #83

    Thanks for the correction.

  36. 86
    Hank Roberts says:

    I’m a reader, not a contributor here. Don’t mistake me for a climate scientist. I read, try to learn, try to ask questions to clarify. Having looked at Margo’s website, I’m done replying to your questions here, it seems you’re trying to be another “auditor” — anonymous, at that. If you think you’re doing science, send it to a refereed journal for help. The “auditors” might as well set up card tables and pull out e-meters, it’s not science.


  37. 87
    Margo says:

    I had two purposes in posting. They are:

    1) I do think it’s important to comment when inline replies are nothing but snark and double standards.

    Contrary to raypierre’s snark about “space aliens”, the standard for a a more or less respectable idea is not that one must “come up with a set of equations saying why….” to support your idea. Heuristic explanations are widely used, and perfectly respectable. Based on your final reply, RC is, in fact, relying on non-mathematical heuristic explanations when discussing the ice core data. (That’s what I thought you were doing when I first read the article.)

    2) If someone had actually come up with a set of equations to explain why the ice core data looks the way it does, I would have loved to have see that. Evidently, no one has come up with one and only heuristic explanations exist. That’s fine with me from a science point of view. ( However, the fact that this bang on explanatory mathematical model does not exist does illustrate that Raypierre was erecting a double standard in his snarky reply.)

    So, thanks for the links to the papers. I’m reading them, and I find them interesting.

    For what it’s worth: I’m entirely unfamiliar with what Astley is talking about. It was the snarky reply that caught my eye. But if Astley’s heuristic argument has some deficiency other than not being described by “a set of equations saying why….” , could someone explain the deficiency? If your position that the idea is just not even fleshed out enough to engage that’s fine. But if an inline reply is warranted, surely it should provide a legitimate criticism.

    [Response: I get your point, but on the specifics of GCR-climate links, Ray is correct. There has not been even one credible estimate of what the radiative forcing for a change in GCR would mean for climate. This is something that clearly is amenable to ‘equations’ and the like, and is the standard by which all potential forcings (CO2, CH4, volcanoes, solar, aerosols etc.) are measured. Until that happens, claims that GCR forcings are the dominant force in climate will continue to be dismissed as they are not based on anything quantitative. We know to a pretty high accuracy what the man-made greenhouse gases have done, there is no comparable estimate for GCR effects. That has nothing to do with heuristic arguments about the glacial-interglacial cycle. -gavin]

  38. 88
    Steve Bloom says:

    Re #82: Margo, you need to read what I wrote. The student paper was useful because it a) contained a good (AFAICT) narrative of how the science had developed up through a little less than two years ago and b) named at least some of the relevant models. IMHO people who aren’t in the field tend to have a hard time really understanding the state of the science without something like that as a guide, so I was very happy to have found it. In any event, I didn’t say the paper included the models or their underlying math, but rather that it named them such that an interested party (you, e.g.) could go look at them to find out about the math.

    Just to restate a little what Gavin said, I think your question betrayed a basic misunderstanding (which is why I thought the student paper would be so useful for you). The behavior of the CO2 around the glaciations can’t be a forcing as such because that would conflict with our understanding of its physical behavior; i.e., it can’t start an increase or decrease by itself. Something else is making it behave that way, which means that it is a feedback to a forcing (or forcings). The way these terms are defined leaves no other option. So, to even refer to a “speculative feedback” betrays a fundamental misunderstanding. Exactly how the behavior of that feedback is modeled is a very interesting question in climate science, and as Gavin says not fully resolved as yet, although it seems clear that the general answer is Milankovitch forcing leading to a combination of feedbacks (e.g. ocean and vegetative) that in turn result in the CO2 change. The test of the models is how well they replicate ice sheet behavior (in terms of timing, size and location), and based on that paper it doesn’t seem like they’re terribly far away from that.

    [Response: In addition, the main point of Severinghaus’ post, referenced at the beginning of this thread, was not to explain the possible mechanisms for the glacial-interglacial CO2 fluctuations, but only to explain that the lead-lag relation cannot be used to infer that CO2 is “caused by” temperature rather than vice-versa. He was shooting down a fallacy in reasoning. As such, it’s a point that is mathematical, and independent of the specific mechanisms causing the CO2 feedback on temperature. Jeff explained this in words, to be more accessible, but it’s quite easy to cook up a pair of differential equations with an external periodic forcing (think Milankovic) which illustrates the point in quantitative terms. By the way, many scientists have proposed specific testable mechanisms for the CO2 glacial-interglacial cycle. They have all been falsified, but that’s just science. The credit goes to the people who have formulated things (like ice cover /gas exchange feedback) that can be quantified to the point of being tested. This is very different from much of the commentary you see from the GCR crowd,notably Mr. Astley’s waving a magic wand and inventing a lower glacial-climate cloud sensitivity to make the problem with the Laschamp Magnetic Anomaly go away. –raypierre]

  39. 89
    Steve Sadlov says:

    RE: #48 – The Dust Bowl years are extremely politically incorrect. They make the 90s look too good.

    [Response: Not at all. Take a look at the midwest regional climate report from Union of Concerned Scientists. We already have hit as many or more days per year of extreme heat (>97F) than there were here in the Dustbowl. Then take a look at where we’re heading in a hundred years. In fact, the Dustbowl makes the future look really, really scary. –raypierre]

  40. 90
    Adrianne M says:

    Hey, want to see how you can change climate?

    Easy and tested. Not politically correct, but still, it happened and we are now seeing the consequences.

  41. 91
    Reid says:

    Actually, Aziz, zero padding the time series can be considered equivalent to interpolating in the frequency domain. In reality, it results in sampling the actual fourier transform of the finite time series on a finer grid so, it’s a little more subtle than just saying it’s an interpolation. I wasn’t criticizing tamino’s methods, just setting the record straight. Also, the number of calculations involved in performing a straight fourier transform rises so fast that, even with modern computers, it can become untenable for a large set of data. And, since there is no sampling theory for unevenly spaced data, the results are often disappointing. I would recommend a least squares type of algorithm based on an ARMA model in that case.

  42. 92
    David Price says:

    Why ice ages happen is a good question. Milancovich cycles have always happened but only in the last 3 million years have they caused ice ages. previous ice house cycles have happened at roughly 250 million year intervals.
    One theory I have read is that the incidence of ice age cycles matches the rotation of the sun around the rim of the Milky Way galaxy. At a certain point in the Sun’s orbit something happens to cause it to dim slightly. This means that at certain stages in the orbital cycle the Sun is not strong enough to melt the ice formed the previous winter, thus causing ice ages. Anybody heard this theory?

    [Response: Sounds like you’re referring to the “Muller and Macdonald” theory. Its all but dismissed now by serious researchers in the field. A nice, concise explanation of why is provided in this Science article by Clark et al (1999): Muller and MacDonald [ R. A. Muller and G. J. MacDonald, Science 277, 215 (1997)] argued that the origin of the 100-ky cycle involves non-Milankovitch changes in the Earth’s orbital inclination, which caused the Earth to periodically pass through a cloud of interplanetary dust. Sedimentary records and calculations of dust flux, however, do not show large changes in extraterrestrial dust accretion [F. Marcantonio, et al., Nature 383, 705 (1996); F. Marcantonio, et al., Earth Planet. Sci. Lett. 170, 157 (1999); S. J. Kortenkamp and S. F. Dermott, Science 280, 874 (1998)], whereas spectral analyses of the marine 18O record of global ice volume suggest that this mechanism is unnecessary [J. A. Rial, Science 285, 564 (1999); A. J. Ridgwell, A. J. Watson, M. E. Raymo, Paleoceanography 14, 437 (1999)]. Hardly a ringing endorsement. Muller’s “death star” hypothesis for explaining the major geological extinctions events including the K/T extinction, hasn’t fared much better. –mike]

  43. 93
    Steve Bloom says:

    Re #90: As has been noted before here on several occasions, a more apt description might be really, really creative but really, really wrong.

  44. 94
    Steve Bloom says:

    Back on the original topic, Martinson and Pitman’s idea doesn’t seem all that far afield from the old Ewing and Donn hypothesis (discussed in the Discovery of Global Warming about halfway down this page).

  45. 95

    IN reading here seeking causefffects patterns & cycles i find rare or no reference to or using natural ‘rebalancing’ weather & climate cycles at all.
    In Gaia Ecology self-regulation is always toward balancing energy for life systems in bioregions & whole biosphere. So omitting ‘balancing’ is fatal flaw in climate modeling & predicting coming patterns causes & effects. That maybe largely why huge climate computer models rarely predict any cycles accurately. ANYONE TRACKING NATURAL CLIMATE BALANCING CYCLES?? thet’re yin/ynag flips happening every day, season, years & longer cycles. Also the patterns of electromagnetic frequency waves we call ‘ionic charges’ in air & water effect weather called pressure fronts, but is also ionic charge zones & MOVEMENTS of weather systems we need to learn how their energy works in simple natural words, not scientease. The only book i know on this is ‘The Ion Effect’ 1980 by Fred Soyka, but weathermen don’t like air ionic charges or lighteing at home,
    its very exciting on TV tho. Our sky does have energy, it ain’t empty vaccum.

  46. 96
    Hank Roberts says:

    Mike, thanks for the Clark (1999) link. The links provided with the free abstract include current work citing that paper; it’s an impressive list.

  47. 97
    Erich J. Knight says:

    Here is my favorite Gaia Ecology self-regulation process:

    After many years of reviewing solutions to anthropogenic global warming (AGW) I believe this technology
    can manage Carbon for the greatest collective benefit at the lowest economic price, on vast scales.

    Below is my review of these efforts in the Academic and private sectors, please forward this to all the experts you know, if you think it merits their time and support.

    Terra Preta Soils Technology To Master the Carbon Cycle

    [edit text and replace with link]


    Erich J. Knight
    Shenandoah Gardens
    E-mail: shengar at
    (540) 289-9750

  48. 98
    Alex Nichols says:

    re Carbon capture and Storage technologies.

    There is no real technological problem with separating out C02 from the airstream of a coal-burning power station. It does make generating electrical power a whole lot more expensive though.

    Sequestration is the big problem and quite honestly, the proposals that are made for it look very suspect. More or less, to dump it and leave it for future generations to deal with, based on some vague and untested ideas.

    Deep ocean storage seems positively dangerous. Even the IPCC report on Carbon Capture and storage admits that it will leak out within a few hundred years.

    Given that it’s the oceans that play the most important role in the Carbon cycle and ocean acidification is potentially disastrous, this is a proposal which should be opposed at all costs.

    “Injection up to a few GtCO2 would produce a measurable change in ocean chemistry in the region of injection, whereas injection of hundreds of GtCO2 would eventually produce measurable change over the entire ocean volume.”

    IPCC Special Report on Carbon dioxide Capture and Storage

    Geological storage is largely an unproven technology. The only real case studies are based on oil industry practices used in exploiting marginal reserves.
    It might also be used by coal companies to extract methane deposits from economically marginal coal seams.

    I think it’s inescapable that the US and China (which produce 54% of the world’s coal) have to reduce their production levels and move towards renewable energy on a massive scale.

    It’s also inescapable that mass transport systems need to move away from using oil

  49. 99

    [[IN reading here seeking causefffects patterns & cycles i find rare or no reference to or using natural ‘rebalancing’ weather & climate cycles at all.]]

    Could you perhaps explain what “natural rebalancing cycles” are? Models do take account of many known cycles, depending on which sort of model we’re discussing. Do you mean the daily cycle, the seasonal cycle, the ENSO cycle, the carbonate-silicate cycle?

  50. 100
    Lynn Vincentnathan says:

    RE #75, 82, 88, I agree that this whole notion of “feedback” is difficult for people, and I don’t think I would have caught onto it so fast, if I had not read articles about positive v. negative feedbacks in the social sciences. I’ll give you a simple example, when we look at the correlation between education and income, that makes a lot of sense to us. That’s why we sweat bullets at the university, so we can get good jobs and incomes (and why we can snicker at the poor, who were lazy & didn’t go for the higher education). So, education is the independent (causal) variable, and income, the dependent (effect) variable.

    But what about a person’s parents’ income? Doesn’t that help them to study during high school (rather than work part-time, or drop out), get better learning aids (encyclopedia sets, etc), then go to better colleges with high tuition fees? So then income becomes the independent (causal variable) and education the dependent (effect) varible, and putting these two cause-effect aspects together, the rich get richer.

    Similarly, GHGs can be an independent or causal variable (a forcing) of warming, and (this is the really scary, super-alarmist part) they can also be a dependent or effect variable, as when warming causes nature to emit GHGs from methane clathrates, permafrost, decay of plants dying from the heat or heat-caused fires (the CO2 lagging the warming in the ice core, extremely confirms this — turns this hypothesis into an evidence-supported theory, contrary to denialists claiming it disproves that CO2 can’t cause GW — since we know some variables can be both effect AND causal variables). And both aspects together in a single system can form a positive feedback loop, in which (in our present case) the initial extra GHGs emitted by humans is causing extra warming, which will cause extra GHG emissions from nature (not to mention reduced albedo, which then causes further warming), which will cause extra extra warming, and so on. Aparently nature has an abundance of these GHGs stored up for just such a mass extinction from severe global warming scenario.

    By looking at that chart above, I’m thinking it’s really really unfelicitous that we just happen to be at a high point in the natural warming (inter-glacial) already, posed after many thousands of years at a warm plateau-peak to start cooling back down. But instead we’re using this high point as a lauching pad to even greater warming.

    I can use this chart as an exhibit for my Eco-House of Horrors next Halloween, with a broken line shooting upward (say, into a ball of fire) from the current high point.

    I’ve been perhaps one of the most extreme alarmists on this site, but now I realize I’ve underdone it; I’ve been sleeping on the job; I’ve severely underestimate the deep doo-doo we’re in. Now don’t come back with platitudes not to worry, because I can see it plainly on the chart — we’re at a high natural peak in the warming-cooling cycle. And it’s being used as a launching pad for still greater heating. This is serious.