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Unlocking the secrets to ending an Ice Age

Filed under: — group @ 28 April 2012

Guest Commentary by Chris Colose, SUNY Albany

It has long been known that characteristics of the Earth’s orbit (its eccentricity, the degree to which it is tilted, and its “wobble”) are slightly altered on timescales of tens to hundreds of thousands of years. Such variations, collectively known as Milankovitch cycles, conspire to pace the timing of glacial-to-interglacial variations.

Despite the immense explanatory power that this hypothesis has provided, some big questions still remain. For one, the relative roles of eccentricity, obliquity, and precession in controlling glacial onsets/terminations are still debated. While the local, seasonal climate forcing by the Milankovitch cycles is large (of the order 30 W/m2), the net forcing provided by Milankovitch is close to zero in the global mean, requiring other radiative terms (like albedo or greenhouse gas anomalies) to force global-mean temperature change.

The last deglaciation occurred as a long process between peak glacial conditions (from ~26-20,000 years ago) to the Holocene (~10,000 years ago). Explaining this evolution is not trivial. Variations in the orbit cause opposite changes in the intensity of solar radiation during the summer between the Northern and Southern hemisphere, yet ice age terminations seem synchronous between hemispheres. This could be explained by the role of the greenhouse gas CO2, which varies in abundance in the atmosphere in sync with the glacial cycles and thus acts as a “globaliser” of glacial cycles, as it is well-mixed throughout the atmosphere. However, if CO2 plays this role it is surprising that climatic proxies indicate that Antarctica seems to have warmed prior to the Northern Hemisphere, yet glacial cycles follow in phase with Northern insolation (“INcoming SOLar radiATION”) patterns, raising questions as to what communication mechanism links the hemispheres.

There have been multiple hypotheses to explain this apparent paradox. One is that the length of the austral summer co-varies with boreal summer intensity, such that local insolation forcings could result in synchronous deglaciations in each hemisphere (Huybers and Denton, 2008). A related idea is that austral spring insolation co-varies with summer duration, and could have forced sea ice retreat in the Southern Ocean and greenhouse gas feedbacks (e.g., Stott et al., 2007).

Based on transient climate model simulations of glacial-interglacial transitions (rather than “snapshots” of different modeled climate states), Ganopolski and Roche (2009) proposed that in addition to CO2, changes in ocean heat transport provide a critical link between northern and southern hemispheres, able to explain the apparent lag of CO2 behind Antarctic temperature. Recently, an elaborate data analysis published in Nature by Shakun et al., 2012 (pdf) has provided strong support for these model predictions. Shakun et al. attempt to interrogate the spatial and temporal patterns associated with the last deglaciation; in doing so, they analyze global-scale patterns (not just records from Antarctica). This is a formidable task, given the need to synchronize many marine, terrestrial, and ice core records.

The evolution of deglaciation

By analyzing 80 proxy records from around the globe (generally with resolutions better than 500 years) the authors are able to evaluate the changes occurring during different time periods in order to characterize the spatial and temporal structure of the deglacial evolution.

Shakun et al. confirm Ganopolski’s and Roche’s proposition that warming of the Southern Hemisphere during the last deglaciation is, in part, attributable to a bipolar-seesaw response to variations in the Atlantic Meridional Overturning Circulation (AMOC). This is hypothesized to result from fresh water input into the Northern Hemisphere (although it is worth noting that the transient simulations of this sort fix the magnitude of the freshwater perturbation, so this doesn’t necessarily mean that the model has the correct sensitivity to freshwater input).

The bi-polar seesaw is usually associated with the higher-frequency abrupt climate changes (e.g., Dansgaard-Oeschger and Heinrich events) that are embedded within the longer, orbital timescale variations. However, numerous studies have indicated that it also sets the stage for initiating the full deglaciation process. In this scenario, the increase in boreal summer insolation melts enough NH ice to trigger a strong AMOC reduction, which cools the North at the expense of warming the South. The changes in Antarctica are lagged somewhat due to the thermal inertia of the Southern Ocean, but eventually the result is degassing of CO2 from the Southern Ocean and global warming. In particular, CO2 levels started to rise from full glacial levels of about 180 parts per million (ppm), reaching 265 ppm 10,000 years ago (or ~2.1 W/m2 radiative forcing), and with another slow ~15 ppm rise during the Holocene.

Figure 1: Simplified schematic of the deglacial evolution according to Shakun et al (2012). kya = kiloyears ago; NH = Northern Hemisphere

The evolution of temperature as a function of latitude and the timing of CO2 rise are shown below (at two different time periods in part a, see the caption). There is considerable spatial and temporal structure in how the changes occur during deglaciation. There is also long-term warming trend superimposed on higher-frequency “abrupt climate changes” associated with AMOC-induced heat redistributions.

Figure 2: Temperature change before increase in CO2 concentration. a, Linear temperature trends in the proxy records from 21.5–19 kyr ago (red) and 19–17.5 kyr ago (blue) averaged in 10° latitude bins with1σ uncertainties. b, Proxy temperature stacks for 30° latitude bands with 1σ uncertainties. The stacks have been normalized by the glacial–interglacial (G–IG) range in each time series to facilitate comparison. From Shakun et al (2012)

What causes the CO2 rise?

The ultimate trigger of the CO2 increase is still a topic of interesting research. Some popular discussions like to invoke simple explanations, such as the fact that warmer water will expel CO2, but this is probably a minor effect (Sigman and Boyle, 2000). More than likely, the isotopic signal (the distribution of 13C-depleted carbon that invaded the atmosphere) indicates that carbon should have been “mined’ from the Southern ocean as a result of the displacement of southern winds, sea ice, and perturbations to the ocean’s biological pump (e.g., Anderson et al., 2009).

This view has been supported by another recent paper (Schmitt et al., 2012) that represents a key scientific advance in dissecting this problem. Until recently, analytical issues in the ice core measurements provided a limitation on assessing the deglacial isotopic evolution of 13C. Because carbon cycle processes such as photosynthesis fractionate the heavy isotope 13C from the lighter 12C, isotopic analysis can usually be used to “trace” sources and sinks of carbon. A rapid depletion in 13C between about 17,500 and 14,000 years ago, simultaneous with a time when the CO2 concentration rose substantially, is consistent with release of CO2 from an isolated deep-ocean source that accumulated carbon due to the sinking of organic material from the surface.

Figure 3: Ice core reconstructions of atmospheric δ13C and CO2 concentration covering the last 24 kyr, see Schmitt et al (2012)

Skeptics, CO2 lags, and all that…

Not surprisingly, several people don’t like this paper because it reaffirms that CO2 is important for climate. The criticisms have ranged from the absurd (water vapor is still not 95% of the greenhouse effect, particularly in a glacial world where one expects a drier atmosphere) to somewhat more technical sounding (like criticizing the way they did the weighting of their proxy records, though the results aren’t too sensitive to their averaging method). There’s also been confusion in how the results of Shakun et al. fit in with previous results that identified a lag between CO2 and Antarctic temperatures (e.g., Caillon et al., 2003).

Unlike the claims of some that these authors are trying to get rid of the “lag,” Shakun et al. fully support the notion that Antarctic temperature change did in fact precede the CO2 increase. This is not surprising since we fully expect the carbon cycle to respond to radical alterations to the climate. Moreover, there is no mechanism that would force CO2 to change on its own (in preferred cycles) without any previous alterations to the climate. Instead, Shakun et al. show that while CO2 lagged Antarctic temperatures, they led the major changes in the global average temperature (including many regions in the Northern Hemisphere and tropics).

It is important to realize that the nature of CO2’s lead/lag relationship with Antarctica is insightful for our understanding of carbon cycle dynamics and the sequence of events that occur during a deglaciation, but it yields very little information about climate sensitivity. If the CO2 rise is a carbon cycle feedback, this is still perfectly compatible with its role as a radiative agent and can thus “trigger” the traditional feedbacks that determine sensitivity (like water vapor, lapse rate, etc). Ganopolski and Roche (2009), for example, made it clear that one should be careful in using simple lead and lags to infer the nature of causality. If one takes the simple view that deglaciation is forced by only global ice volume change and greenhouse feedbacks, then one would be forced to conclude that Antarctic temperature change led all of its forcings! The communication between the NH and Antarctica via ocean circulation is one way to resolve this, and is also supported by the modeling efforts of Ganopolski and Roche. This also helps clear up some confusion about whether the south provides the leading role for the onset or demise of glacial cycles (it apparently doesn’t).

A number of legitimate issues still remain in exploring the physics of deglaciation. For instance, the commentary piece by Eric Wolff references earlier deglaciations and points out that solar insolation may have increased in the boreal summer during the most recent event, but was still not as high as during previous deglacial intervals. It will be interesting to see how these issues play out over the next few years.


  1. P. Huybers, and G. Denton, "Antarctic temperature at orbital timescales controlled by local summer duration", Nature Geoscience, vol. 1, pp. 787-792, 2008.
  2. L. Stott, A. Timmermann, and R. Thunell, "Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming", Science, vol. 318, pp. 435-438, 2007.
  3. A. Ganopolski, and D.M. Roche, "On the nature of lead–lag relationships during glacial–interglacial climate transitions", Quaternary Science Reviews, vol. 28, pp. 3361-3378, 2009.
  4. J.D. Shakun, P.U. Clark, F. He, S.A. Marcott, A.C. Mix, Z. Liu, B. Otto-Bliesner, A. Schmittner, and E. Bard, "Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation", Nature, vol. 484, pp. 49-54, 2012.
  5. D.M. Sigman, and E.A. Boyle, "Glacial/interglacial variations in atmospheric carbon dioxide", Nature, vol. 407, pp. 859-869, 2000.
  6. R.F. Anderson, S. Ali, L.I. Bradtmiller, S.H.H. Nielsen, M.Q. Fleisher, B.E. Anderson, and L.H. Burckle, "Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2", Science, vol. 323, pp. 1443-1448, 2009.
  7. J. Schmitt, R. Schneider, J. Elsig, D. Leuenberger, A. Lourantou, J. Chappellaz, P. Kohler, F. Joos, T.F. Stocker, M. Leuenberger, and H. Fischer, "Carbon Isotope Constraints on the Deglacial CO2 Rise from Ice Cores", Science, vol. 336, pp. 711-714, 2012.
  8. N. Caillon, "Timing of Atmospheric CO2 and Antarctic Temperature Changes Across Termination III", Science, vol. 299, pp. 1728-1731, 2003.

139 Responses to “Unlocking the secrets to ending an Ice Age”

  1. 1
    Edward Greisch says:

    Figure 3 doesn’t come up.

  2. 2

    Excellent summary, Chris; thanks! Quite clear & readable.

    (Only slightly marred at the end by my pet peeve redundancy: “solar insolation.” People write this all the time, presumably not realizing that “insolation” already covers the “solar” bit–but since it had been explained earlier in the piece that the term is derived from (“INcoming SOLar radiATION”), this reference was jarring. OK, I’ll shut up about this now.)

    (Oh, and figure 3 didn’t display, but this may be my browser, not the article.)

    Again, thanks!

  3. 3
    Edward Greisch says:

    The link “Shakun et al., 2012 (pdf)” leads back to this article.

  4. 4

    My comment is in regarding the the Antarctic data CO2/temperature record.

    I am interested in the lags in the climate system and to see how the limit cycles may respond to minor amounts of positive feedback, such as that due to CO2 outgassing with temperature. I can understand how the feedback of CO2 release with temperature increase is weak and self-limiting but it has to play at least a part of the process. We also obviously see the limit cycles with the seasonal ripples on the Mauna Loa data. This is my analysis:

    The Vostok data is in the first part of the analysis and then I look at Mauna Loa data at the end. I estimate 3 PPM/degree transient and 10 PPM/degree long-term sensitivity due to outgassing.

    The other significant point in all this is that the adjustment time of CO2 is different for naturally induced temperature changes than it is for artificial releases. This hasn’t really been clearly articulated as far as I can tell, but the implications are huge when one compares our current situation to historical glacial cycles.

  5. 5
    Pete Dunkelberg says:

    Link to Schmitt et al. 2012.

  6. 6
    JBL says:

    Edward Greisch, as has already been explained to you in an earlier thread, the citation links in the article lead to the bibliography at the bottom of the article. But let me put in another vote for seeing figure 3!

  7. 7
    tamino says:

    Very interesting stuff. I’ll mention that although orbital variation (precession) causes opposite insolation changes in the two hemispheres, axial tilt (obliquity) variation causes synchronous insolation changes in the two hemispheres. Precession dominates *midsummer* high-latitude insolation (the usual Milankovitch metric), but obliquity has a stronger influence on Huybers’ notion of “summer heat” (which takes into account the astronomical influence on length-of-season.

    I’m also intrigued by Raymo’s idea that an important factor is that during recent glacial cycles, the ablation zone of N.Hem ice sheets is land-based but that of S.Hem ice is ocean-based. This raises the possibility that changes in sea level can profoundly affect the S.Hem ice — wasting of N.Hem ice sheets can raise sea level, “unpin” and destabilize the S.Hem ice, helping make the changes global. This may also help explain why, before about 800 ky ago, glacial cycles were dominated by the 41 ky obliquity cycle, while precession had very little effect. In those colder, older times, the S.Hem ice edge was land-based so the influence of sea level changes was not a factor.

  8. 8
    Fred Moolten says:

    Chris – Thanks for a very informative overview of our evolving understanding of the last deglaciation. I don’t think there was much prior uncertainty in the literature over the general notion that orbital forcing changes were an initiating factor and that consequent rises in CO2 contributed a major subsequent warming influence, but the timing (regional vs global) and the interaction between the hemispheres has not been well illuminated. The recent work, particularly including Shakun et al, is beginning to paint a clearer picture, although important details are still missing.

    I’ll comment on two specific points you raise. The first is to emphasize your point that degassing of CO2 from the oceans is not simply a matter of warmer water reducing CO2 solubility, and that important additional factors include changes in wind patterns, reduction in sea ice cover to reveal a larger surface for gas escape, and upwelling of CO2 from depths consequent to the changing climate patterns.

    The second point relates to a WUWT analysis by Willis Eschenbach challenging Shakun et al, and I bring it up because I expect some WUWT readers may also visit here and may wonder what was wrong with Willis’s analysis.

    Unfortunately, it started out with a serious error (unless I misread what he wrote), and that error more or less makes it impossible to extract a meaningful interpretation of the temperature data from the way he transformed the data. As a preface, I’ll point out that temperature change can’t be expected to be the same everywhere in a global survey. There are major differences dependent on latitude, ocean basin, proximity to specific land masses, and in the case of some proxies, seasonal effects. Different proxy records should reflect these differences and differ therefore in the magnitude of recorded temperature change. What Eschenbach apparently did was to “standardize” the temperature data instead of leaving it alone. He took each proxy record (typically composed of values rising over time), treated it as a normal distribution, computed a standard deviation, and then divided the values from that proxy by its SD to yield “standardized” values. What this does, of course, is tend to “compress” large temperature changes in some proxies toward the smaller values from other proxies, to the extent that the larger changes are accompanied by larger SDs, which is often the case, thereby homogenizing the extent of actual temperature change. How much this process distorted the actual record isn’t known, but it almost certainly did, and was unnecessary.

    Surprisingly, I don’t think any of the many dozens of WUWT readers who commented picked up on the error, which makes me wonder about their level of climate sophistication.

    I don’t think Shakun et al is the last word on this subject, but it offers valuable clarification of the timing and regional distribution of the CO2/temperature relationship.

  9. 9
    Chris Colose says:

    Edward- Click on the PDF link; all links to papers will go lead back to the reference section of the article, to which you need to click on the corresponding DOI.

  10. 10
    BillS says:

    Thanks or the summary and pointing out Shakun, et al. As you point out a number of issues remain. What initiated the global temperature rise about 20 kya? It’s been suggested (Wolff alludes to it) that the northern hemisphere’s ice sheets reached such a vertical extent as to modify atmospheric circulation in the mid- and upper-latitudes. If so, would such changes be felt globally? Could such changes have occurred rapidly enough to bring on the increase in CO2 about 17 kya? If you combine orographic effects with changes in insolation, is this enough to initiate the temperature rise?

  11. 11
    Unsettled Scientist says:

    I just wanted to let the RC folks know that this showed up in my RSS feed several days ago. I’m not sure what happened, if it was showing a post under construction or if it was temporarily published and then removed. Just a heads up so you all can review your processes and make any refinements to prevent posts not yet ready for public consumption from being accessible. Also, for some reason the site is in French, the field is Nom not Name, the button is Dites-le not Say-it.

  12. 12
    sydb says:

    Thanks, Chris. Yet more of the details of the jigsaw appear. The broad picture has been clear for a long time, but any small holes are always picked on by those who stand to lose their unsustainable way of life.

    This is no surprise that CO2 does not lead everywhere, after all something has to start the process. Then the feedbacks begin to take over. It’s a bit like a Schmitt trigger, where the input has to reach a certain level before anything happens. Then feedback kicks in and the change is dramatic.

  13. 13
  14. 14
    David B. Benson says:

    I didn’t keep the links but there is at least one d18O study from the Pacific Warm Pool which clearly indicates that first the deep ocean warmed there, followed later by the CO2 increase and then the shallow ocean warmed, leading to the LGM to Holocene transition.

  15. 15
    owl905 says:

    @Fred Moolton 8 – thanks for the Tony T Watt link. The Eschenbach response is pretty funny (don’t understand your problem with his ‘standardized’). He basically itemizes nearly all the proxies reaching their peaks after the CO2 peak is reached … while trying to claim the data “is all over the map”.

    Excellent article here. No surprise that the Shakun paper has stirred up Mr. Watt and other pollution priests – years of budgie lessons teaching “CO2 lags temperature rise” took a head-shot.

    On the missing ‘issues’; here’s some outside recollections. There are studies of Holocene-onset fossils showing animal downsizing trends along the Caribbean Antilles (chain turned islands). There is the Bosporus portal ‘Sea of Death’ isolation. 14,000 years ago the Dead Sea was finally shut off from the Mediterranean. Tamino’s point about ocean levels may have a corollary in the re-organization of regional climates and air currents. Milankovitch is nice, but the big cycle trigger may need the lower-ocean context to work.

  16. 16
    nuclear_is_good says:

    Very good article, and not a second too early given the constant barrage of denial and misrepresentation around the Shakun paper started by people like Michaels and Idso, promoted for the WUWT crowd by ignorant conspiratards like Don Easterbrook and Willis Eschenbach and more recently also pushed by Motl and Shaviv.

    I would also note that Schmitt et al., 2012 have indeed provided a key scientific advance on the topic of the source of the CO2, but that it still seems that things are far from being definitely settled (and the role of permafrost might still be a lot bigger than expected), plus the mystery of the 14C isotope that is clearly mentioned at the end of Schmitt et al., 2012!

  17. 17
    Edward Greisch says:

    Figure 3 still does not work in either Safari or Firefox.

  18. 18
    Ron Manley says:

    I think this is a topic well worth further study. My hunch is that when we understand better the Milankovitch ‘trigger’ and ‘propagation’ mechanisms we will have a clearer idea of how other aspects of climate interact. I’ve tended to accept without questioning the conventional view that the Milankovitch radiation at 65N in July is critical. Around this latitude a higher proportion if the earth is land rather than ocean and is covered (at least at present) with Boreal forests which have a high snow-covered/bare-branch difference in albedo. However 65S in January has a similar radiation profile to 65N in July except for the precession of the axis component which has the effect of introducing a circa 10,000 year phase difference. Could it be (and I’m just floating an idea) that exit from (or entry into) an ice age starts in the north and is reinforced in the south. After all the sea/ice albedo difference is large and the southern oceans are more likely to be part of an ocean mechanism for propagating the Milankovitch effect.

  19. 19
    Edward Greisch says:

    Fig 3 works now. Thanks.

  20. 20
    Bob Koss says:

    I see one of the Shakun authors is Bette Otto-Bliesner. She is also a lead author of the paleo chapter in ar5. It will be interesting to see how much weight is given to this study relative to previous conflicting studies.

  21. 21
    Ray Ladbury says:

    Bob Koss,
    Conflicting studies like…?

  22. 22
    Steve Fish says:

    Bob Koss,
    Implications of impropriety with no evidence whatsoever is a favorite tool of science denialists and those with a nasty insult hobby.

  23. 23
    Brian Chow says:

    Fred Moolten’s analysis is highly illuminating. I might even add (correct me if I’m wrong?) that it reminds me of the coefficient of variation. I can remember at least that much from engineering statistics. Except a normal COV would divide the standard deviation by the mean, providing a dimensionless number for the magnitude of dispersion.

    So, if one does takes the 1/x of dispersion, it appears that logically we obtain a measure of non-dispersion or precision in the data. However it has a completely different meaning from the data itself.

  24. 24
    Pete Dunkelberg says:

    We aren’t settling for just ending an ice age the usual way:

  25. 25
    Hank Roberts says:

    Bette L. Otto-Bliesner
    University Corporation for Atmospheric Research
    Publications: 96 | Citations: 2287 | G-Index: 46 | H-Index: 27
    Collaborated with 303 co-authors from 1993 to 2011; Cited by 4047 authors

    Clearly highly suspiciously connected to the previously discovered Social Network, must be a conspirator, no true scientist would cooperate so widely with so many other scientists

  26. 26
    CRV9 says:

    Sorry to interlude but I’ve had this question for a long time and didn’t know who or where to go to ask. I’m a layperson with only highschool education so please go easy on me.

    This is about the temperature didn’t seem to increase/change in last 10~15 years in relative to increase in CO2. But ice-melts are increasing around the globe at the same time, though.

    My question is that does it require extra energy/heat to melt ice? I remember I learned that it takes extra energy(to cool) to freeze 0 degree C water to 0 degree C ice in school a long time ago. So I’d think it takes extra heat/energy to melt 0C ice to 0C (freezing) water, eventhough temperature wouldn’t change? The proccess of melting ice itself, changin a state of solid to liquid is part of the temperature rise, eventhough actual temperature wouldn’t go up?
    I’m sure the scientists are already considering this but I’m just curious.
    If anybody can just drop me a line or two to clear my mind I’ll appreciate it. Thank you.

  27. 27
    David Beach says:

    Could we please have the time axis consistent with the past (negative) increasing to the left and the future increasing to the right (positive)?

  28. 28
    Ray Ladbury says:

    First, welcome. Sincere questions are always welcome.

    Second, if you can find a thread marked “Unforced Variations,” that’s an open thread, so your question won’t be “off topic”.

    Third, yes, ice does take a lot of energy to melt. However, the amount of ice being melted isn’t large enough to significantly affect the rate of warming (<10%, I think last time I looked). However, there is also a huge reservoir of cold water in the deep oceans. Some of the heat may be going there.

    Finally, look up Rahmstorf and Foster 2011–it shows that if you account for El Nino, volcanic eruptions and changes in solar forcing, the warming has continued apace. Take care, Ray

  29. 29
    Chris Colose says:

    CRV9- Yes, it takes energy to melt the ice which won’t go into temperature manifestation. This is actually important for the seasonal cycle at high latitudes.

    David Beach- Sorry, I just pulled those figures from the papers; paleoclimatologists have weird customs with time axes and showing multiple graphs with lots of squiggly lines on just one figure. You just have to look at them for an extra minute to interpret properly :-)

  30. 30
    Jim Eager says:

    CRV9, re the meme that “temperature didn’t seem to increase/change in last 10~15 years”, see the post at Skeptical Science, which shows that is simply not true when you allow for the natural variation of El Nino/La Nina and volcanic eruptions.

    Warming, if not actual temperatures, has clearly continued unabated. For example, note that the most recent La Nina episode (2010-2011) was warmer than all previous La Ninas, and warmer than all but the three most recent El Ninos. In other words, what was once a cool exursion (La Nina) is now warmer than past warm excusions (El Nino).

  31. 31
    Dan H. says:

    Yes, it does take ebergy to melt ice, which would not manifest itself in a temperature change. However, you may want to read some of the responses on the Arctic sea ice volume thread, which discusses this issue in depth. One of the theories discussed is the prevaling winds and currents affecting the sea ice much more than temperature. Cheers.

  32. 32
    owl905 says:

    Ray Ladbury wrote at 27 “However, there is also a huge reservoir of cold water in the deep oceans. Some of the heat may be going there.”

    About 90% of the heat is initially absorbed by the oceans. The NOAA calc is that about 16% (not sure if that’s from-total or from-ocean) goes into the deeper layers. Gavin Schmidt has had some quotable posts about it here.

    @’the lack of heating’, the best comment was from a Royal Society spokesman in 2007 around the time of the Keenlyside ‘AMOC shutdown’ simulation … ‘global warming could pause … even for a decade’. La Nina’s, volcanic activity … even violent cold-weather ejections from both polar regions … the discussion has turned into sitting and waiting for the next bubble from the teapot water. Responding is just ‘swinging at a pitch in the dirt’.

  33. 33
    GlenF says:

    Thanks Chris, Suny, for an excellent piece. It’s been fascinating to watch this story unfold over the last couple of decades. For me, the AGW lightbulb moment came with the Vostok CO2 record. The ice age orbital correlation is old knowledge; there all those years ago in my high school geology text*, along with the observation that the insolation change is way too small to provide a simplistic explanation. CO2 provided that explanation … but wait, that could only mean these guys must be right … oh shit.

    Then we had the lead / lag thing, which changed nothing much, despite absurd obfuscation. Temperature increase triggers carbon cycle response which triggers bigger temperature increase, and that’s supposed to be a surprise? And now we finally have the mechanism.

    The pieces are not quite all there, but the picture is clear.


    [*Holmes’ famous tome; the only high school text still on my shelf. Yes I know, an odd choice at that level, but a good one I think … from an odd but rather good teacher.]

  34. 34

    @ Dan H.

    One of the theories discussed is the prevaling winds and currents affecting the sea ice much more than temperature.

    Pretty much everything you say is based on dissembling, isn’t it? Nice not to hamstring one’s agenda with such mundane things as citations to the peer-reviewed literature published in reputable journals.

    But then it wouldn’t be called hand-waving then, would it?

    Apropos ReCaptcha: Selface except

  35. 35
    t marvell says:

    I’m also an amateur trying to make sense out of climate trends. The situation is confusing. As you say, there is no apparently connection between CO2 levels and recent temperature trends. I’ve done regression studies that show this, using data from 1969 on. That’s true even when CO2 levels are lagged out to 6 years. It’s also true even when controlling for el_nino and volcanos, no matter what Rahmstorf and Foster say.
    The climate scientists’ response is that one cannot judge by short term trends. But that is not a good argument; they emphasize the temperature increases from about 1977-97 as confirming their theories.
    The scientists should do a better job of addressing their critics. They are losing the public-opinion battle against the energy interests. Their science is largely wasted if they cannot do an effective job of persuading the public and policy makers.
    In the end, the answer to your question seems to be that the CO2 greenhouse effect, according to theory, works stronger in cold temperatures. CO2 has less direct effect in lower latitudes. The temperature in the artic (but not the anartic) has increased much more than the rest of the globe, as theory would suggest. Thus the ice melt. My regression analysis shows a sizeable impact of CO2 on artic land temperatures. More CO2 leads to higher temperatures there a few months later.
    Artic temperature and ice are the canary in the mine, an advance warming. The effect on the rest of the world seems to depend largely on a complicated, and presumedly irratic, set of forces that transfer heat around. This relationship is diffuse enough that one might not expect a noticeable relation between global CO2 and temperature.

  36. 36
    wayne job says:

    It will be found through scientific endeavour that our climate is controlled by external forces.

    What we get is weather as our world tries to come to reach equilibrium with ever changing imputs.

    The glacial interglacial cycle is like a sine wave and the only possible explanation is in our perambulations around our galaxy and the effect on our solar system.

  37. 37
    Marcus says:

    Great, T marvel

    “I’ve done regression studies that show this, using data from 1969 on. That’s true even when CO2 levels are lagged out to 6 years”

    Where can we look them up?


  38. 38
    Ray Ladbury says:

    T. Marvell,
    Huh? Dude, have you even bothered to look at the physics of climate? Climate is noisy. If you look at the period from 1977-1997, it is also quite easy to pick 10 year periods that show little or no net warming, and yet warming over the period is significant.

    And actually, if you look at the warming over the past 35 years, the correlation with delta ln(CO2) is quite significant. The purpose of science is to yield an understanding of the phenomena being studied. Period. It is not to persuade morons who’ve never taken a frigging science class–whether those morons are at you family’s Thanksgiving dinner table or in the halls of Congress.

    Roy Schwitters referred to the current generation of ideologues as “the revenge of the C students”. Of course, that was back in the ’80s and ’90s. We’ve probably moved on to the D students by now. Maybe the answer is to ask the smart kids.

  39. 39
    Jim Eager says:

    Sounds like t marvell needs to read the John Nielsen-Gammon post at Skeptical Science as well. Here’s the link again:

  40. 40

    #35–wayne j.–“The glacial interglacial cycle is like a sine wave and the only possible explanation is in our perambulations around our galaxy and the effect on our solar system.”

    Um, no, it’s not:

  41. 41
  42. 42
    Jim Eager says:

    Sorry, here’s the corrected link to the John Nielsen-Gammon post at Skeptical Science:

  43. 43
    Ray Ladbury says:

    Wayne Job,
    Party on, Dude!

  44. 44
    SecularAnimist says:

    t marvell wrote: “The scientists should do a better job of addressing their critics. They are losing the public-opinion battle against the energy interests.”

    Paid propagandists are not “critics”, and your claim about public opinion is a blatant falsehood:

    “… a just-released poll from the Yale and George Mason climate change communication programs reveals the lie in this claim. 63 percent of respondents said the United States should move forward to reduce greenhouse gas emissions, regardless of what other countries do … In the same poll, the public supported — by a margin of 63 percent to 37 percent — requiring electric utilities to produce at least 20 percent of their electricity from renewable energy sources, even if that would cost the average household an extra $100 per year.”

    And a recent Gallup poll found that 65 percent of Americans support “imposing mandatory controls on carbon dioxide emissions/other greenhouse gases”.

    And keep in mind, two-thirds of the American people support mandatory controls on GHG emissions in spite of the relentless onslaught of fossil fuel industry propaganda, and the lies of commission and omission, that have dominated the public discourse for a generation.

    The claims of global warming deniers that public opinion is on their side are as bogus as their pseudo-science, pseudo-economics and pseudo-ideology.

    Perhaps YOU “should do a better job” of addressing reality.

  45. 45
    MARodger says:

    t. marvell @34
    You say “…there is no apparently connection between CO2 levels and recent temperature trends.” What “connection” would you expect there to be?
    Before you answer, do remember that climate adjusts to a CO2 forcing over many decades such that the rising CO2 prior to Keeling’s first measurements would even now still be a component in today’s changing climate, albeit a minor one. And also do remember that CO2 is not the only positive anthropogenic forcing and, although it is increasing faster than the rest, it is presently not much more than half of such forcings. And let’s not forget the negative anthopogenic forcings. And the natural ones too.

    So what “apparently connection (sic)” should we be looking for?

  46. 46
    CRV9 says:

    I just like to thank you all for replying to my question. It was very kind of you. I will check the ‘Unforced Variations’ section one day.
    As part of the public, I must say that we, most of us, only have highschool level understandings or less. We’re usually too busy making our ends meet. However we all have the same one vote. Thank you, again.

  47. 47
    t marvell says:

    Eager – 38&41. About the fact that the temperature growth curve seems to grow consistently upward if you factor in El_Nino. These studies are suspicious – they look at El_Nino several months prior, using that to smooth the curve. The question is why they selected these lags. It looks like a case of fishing for the best model to get the results you want. In fact my regression analysis shows that El-Nino has a huge impact on temperature, but only for the same month (witout lag), with a lesser impact lagged one month, and nothing for additional lags. Also it’s not really an “impact” – temperature is an element of El_Nino measures, so when one says that El_Nino affects temperature, one is largely saying that temperature affects temperature, an identity.

  48. 48

    #43–To be fair though, SA, the deltas in the Gallup poll are unfavorable, even if the overall numbers are not. I don’t think that’s a long-term trend, which is to say that I think you are more right than not, but unfortunately there is some evidence suggesting the denialist machine is having some effect.

  49. 49
    James S says:

    “Artic temperature and ice are the canary in the mine, an advance warming.”

    Come off it T Marvel, next you’ll be telling us that Global Sea Ice is above average.

    Read more at Sks to get the facts straight.

  50. 50
    Jason says:

    I know this off topic, but I wanted to point everyone to the great piece of science journalism that Justin Gillis wrote in the NYT today I thought he really presented that case well including links to the relevant articles. He actually presented a “balanced” approach by treating Lindzen with respect, but not presenting his argument as if it had equal evidence supporting the his claims.