RealClimate

Comments

RSS feed for comments on this post.

  1. As a non-expert (to put it as flatteringly as possible) I’ve never been able to understand how these ice core data relate to estimates of CO2 levels v. global temperatures from deep-time periods such as the Carboniferous or Ordovician. My skeptic friends always point these ancient periods out to me in an attempt to dispel the idea that CO2 effects temperature. I know they are wrong, but can’t come up with an argument against it. Any ideas? Why were Co2 levels so high in the past with relatively low global temperatures? Is the Quaternary earth a different ball-game?

    [Response: It gets more difficult to reconstruct atmospheric CO2 levels further back in time than the ice cores go, but in general, as best it can be done using "proxy" determinations from isotopic measurements or what have you, periods of warmth coincide with higher CO2 in the past. There's no argument against the CO2 impact on climate from ancient times. Actually, if CO2 were not a greenhouse gas, it would be impossible to explain past climate states. David]

    Comment by DonaldK — 12 Dec 2007 @ 1:25 PM

  2. > What would be really cool is if we could get CO2
    > and methane records back to say 2 million years ago

    I imagine this calls for finding sediments — much harder to drill ocean bed sediment than icecaps, I know there’s a lot less done and very little correlation yet across sites; Gavin remarked on that earlier after his trip to China as a current issue.

    If the ice cores and sediment cores can be correlated as far back in time as the ice is available, then the older sediment will have that as a basis for confidence.

    [Response: Yeah, we got sediments a plenty going back millions of years, but they don't have bubbles of air in them. No decent isolated water samples from long ago either, more's the pity. David]

    Comment by Hank Roberts — 12 Dec 2007 @ 1:49 PM

  3. I have heard that pollen samples can extend back a lot further than ice. Is that accurate? Are they equally useful, when it comes to working out what the paleoclimate was like at a particular time?

    Richard Alley mentions them briefly in chapter five of “The Two Mile Time Machine.”

    [Response: In principle they could go back further, but they don't tell CO2 concentrations. David]

    Comment by Milan — 12 Dec 2007 @ 2:04 PM

  4. Yesss , Christmas time! RC keeps on giving !
    Thanks a lot for the reporting !

    so one more question: do we know precisely the mecanisms by which carbon is released (from where ?) to the atmosphere during deglaciation times ? i mean, do ocean warming, circulation changes, soil de-freezing (while vegetation probably develops, so acts as a sink), explain it all ?

    [Response: Not in my opinion. You can clobber an ocean carbon cycle model with everything you can think of, and it won't bring the atmospheric CO2 concentration down to 200 ppm, let alone 172. Temperature can do some of it, and a high-carbon deep water mass is beginning to emerge in the reconstructions, but no one has a mechanistic model which can explain the CO2 cycles. David]

    Comment by ICE — 12 Dec 2007 @ 2:07 PM

  5. I am just curious whether there is anything new to report on the lag between CO2 and temperature from this new dataset?

    [Response: No, that part of the record is finished. David]

    Comment by Frank R — 12 Dec 2007 @ 2:09 PM

  6. “There’s no argument against the CO2 impact on climate from ancient times.” But correlation alone cannot be an argument, can it? How do you explain the lag between temp and CO2? Isn’t this an argument against causation?

    Comment by Mitchell — 12 Dec 2007 @ 2:40 PM

  7. I’m a non expert in climate science, but I was wondering about the correlation between temperature change and solar irradiation (Milankovitch cycles). Is there a phase lag or delay in the temperature change relative to the change in solar radiation. I guess what I’m driving at is – does CO2 concentration have a damping effect or delaying effect on the on the temperature change relative to the change in solar radiation.

    [Response: No. It has an amplifying effect. - gavin]

    Comment by KenH — 12 Dec 2007 @ 2:42 PM

  8. Re #1 Donald

    Dana Royer has recently compiled the proxy CO2 and temperature data covering the entire Phanerozoic period:

    see “CO2-forced climate threasholds during the Phanerozoic” (2006) Geochim. Cosmochim. Acta 70, 5665-5675

    In general, the temperature proxies rise and fall pretty well in line with the CO2 estimates throughout this period (back over 500 million years). Obviously in the very deep past a stronger greenhouse effect was required to maintain reasonable temperatures in the light of a weaker solar output. So for example right up to “even” 100 million years ago (MYA) atmospheric CO2 levels had to be above 1000 ppm for the Earth not to be in a cool period, and CO2 levels below 500 is considered to be the threshold for full glaciations.

    Interestingly even Jan Veizer, who not very long ago was publishing a paper with Shaviv asserting that the cosmic ray flux variation was the dominant driver of the Earth’s climate in the deep past, has just published a paper indicating that it is actually CO2 levels that couple with the earth’s climate back through the Palaeozoic.

    R.E. Carne, J. M. Eiler, J. Veizer, K. Azmy, U. Brand & C. R. Weidman (2007) “Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era” Nature 449, 198-202.

    I’m not sure there are any significant periods where cold temperature proxies are associated with high CO2 proxies. For example, Veizer et al correct a temperature (around 450 MYA) associated with a high CO2 that was previously considered to be cold (about 3 oC cooler than today). Their reassessment indicates that that period was actually 7 oC warmer than now!

    Comment by Chris — 12 Dec 2007 @ 3:21 PM

  9. Note, too, that there are no ice cores from the Cambrian or Ordovician. They’re all from the Quaternary.

    Temperature doesn’t just depend on CO2, but on other greenhouse gases, the albedo of the surface, the arrangement of the continents, etc. If all else is kept equal, more CO2 means higher temperatures, but early ages were not like today, so there is no reason to suppose a simple one-to-one link to hold.

    Comment by Barton Paul Levenson — 12 Dec 2007 @ 3:24 PM

  10. I thought this was a science blog. This is no place for such a personal attack on Richard Lindzen. If I were him I would demand a public apology, but he is probably too much of a gentleman to do that.
    Shame.

    [Response: I apologize. And I'll sell you the bridge myself. David]

    Comment by AD — 12 Dec 2007 @ 3:55 PM

  11. RE “The Antarctic CO2 record has spawned countless internet rants about the CO2 lag behind temperature…”

    I really don’t know why skeptics are so gleeful over warming causing CO2 to increase. It was only when I learned about that I became much much more concerned about GW.

    It’s one thing that CO2 causes warming in a somewhat linear fashion (I know it’s sort of a log function). But it’s really a lot more serious that warming could cause an increase in CO2 levels, causing increasing warming, causing increasing CO2 levels, and so on to ? oblivion ?

    Is this thanatos (Freud’s death wish) at its worst on their part? Do they really think they have an argument. It just strengthens our need to be concerned about and address GW ASAP.

    Comment by Lynn Vincentnathan — 12 Dec 2007 @ 4:16 PM

  12. D’oh. I didn’t notice that session when picking out my lists of things to see. (It’s too bad AGU doesn’t have a mechanism for highlighting sessions/presentations that are likely to be of broad interest.)

    Did they happen to say anything about when the data is likely to reach the archives? Presumably there will have to also be a paper publication first. I’ve been waiting to update my ice core carbon figure for well over a year after being told that the full record was coming “soon”. Not to mention that there was already at least one press release about “800 kyr” carbon dioxide back in mid-2006. It is nice to know that things are finally coming to completion.

    Incidentally, most of the people I’ve talked to about it seem to think that one can probably get ~1.5 Myr of usable ice out of Antarctica with a truly optimal site, but that’s probably about the limit of what’s achiveable.

    [Response: The paper's submitted to Nature, ought to be out within a few months. You weren't the only one who missed the talk, it was at 0800 and not very crowded. David]

    Comment by Robert A. Rohde — 12 Dec 2007 @ 4:17 PM

  13. Do any scientists speculate that the apparent lag between CO2 and temperature in the ice core record is a false reading, and that there might be some unrecognized factor that makes the lag show up in ice cores?

    [Response: The lag is very uncertain, but there are good physical reasons to expect it to be there, so it isn't very troubling. The basic issue is that deep ocean carbon takes centuries to adjust to new surface conditions (winds, ocean currents, biological activity). - gavin]

    Comment by Mark R — 12 Dec 2007 @ 4:50 PM

  14. re: 10. See http://www.realclimate.org/index.php/archives/2007/04/lindzen-in-newsweek/

    Scientific shame on Lindzen, indeed.

    Comment by Dan — 12 Dec 2007 @ 5:22 PM

  15. Re: #8

    Chris,

    Thank you for bringing up Came et al, 2007. When the paper was published I thought that RC would be all over it… and I even e-mailed it as a suggested topic… but alas, nothing ever came of it.

    I was taken aback by that paper as well. Does this mean that Veizer has reversed his stance on GCR’s, though? I have not encountered any statements from him that would affirm that… although one would think that this would be a serious blow to his original correlation.

    Nonetheless, it appears that Veizer is still claiming that CO2 was anomalously high during the Late Ordovician icehouse. I have a few problems with his assertion. First, it seems to be based on reconstructions by Yapp, Royer and Berner, which are rather broad in scope (especially in the case of Yapp, 1992). Saltzman and Young’s (2005) detailed isotope stratigraphy of the Mid-Late Ordovician reveals several brief but major d13C excursions that seem to correspond with glacial maxima. These excursions may correspond with rapid drops in pCO2, but no one (to my knowledge) has done any detailed pCO2 stratigraphy from that time period.

    Secondly, Ordovician paleosols were developed prior to the evolution of vascular land plants. Thus, it becomes more difficult to apply Cerling’s model. Furthermore, if Saltzman is right about the icehouse being relatively brief (on the order of 10^4-10^6 years) then one could easily miss those paleosol horizons… especially if one also considers that (as a general rule) paleosols are more likely to develop during wetter, interglacial periods.

    Comment by Bruno — 12 Dec 2007 @ 6:42 PM

  16. So… this must be an update of the Jouzel et al (2007) paper that appeared in Science earlier this year. Did they mention what the CO2 age uncertainty is for the period 650k-800k? Does it become significantly greater with depth?

    Comment by Bruno — 12 Dec 2007 @ 6:46 PM

  17. Re Mitchell @ 6: “But correlation alone cannot be an argument, can it? How do you explain the lag between temp and CO2? Isn’t this an argument against causation?”

    No, it’s not. Rising CO2 is not the initial cause of interglacials, but rather a feedback to the initial warming caused by increasing solar insolation, as are changes in albedo as the ice retreats. But then this increase in CO2 leads to yet more warming through the greenhouse mechanism, until equilibrium is gradually reached. [Note: equilibrium is a dynamic state, not a static one.] Since we’re nearing the end of the current interglacial, we’ve been at this natural equilibrium for a long time now. The CO2 we are releasing into the atmosphere by burning fossil carbon fuels is clearly not a feedback to an already underway warming, it is a new forcing.

    BTW, there have been times in the distant past where an increase in greenhouse gases was a forcing rather then a feedback. They were not times that you would have wanted to witness first hand. Look up the Permian-Triassic transition (251M BP), Triassic-Jurassic transition (200 M BP), Paleocene-Eocene Thermal Maximum (55M BP), for example.

    Comment by Jim Eager — 12 Dec 2007 @ 7:13 PM

  18. Wow, everything happening very fast. I do have one question. As I understand, the resolution in antarctic cores is very bad after a (relatively) small amount of time, which is why Greenland cores are used more for the last 100k or so, but is this just for CO2 or temp as well? Or can you just see the “general picture” without details?

    [Response: Time resolution is better in Greenland, but the CO2 in the bubbles there is contaminated by CaCO3 dust + acid aerosols, so CO2 only comes from Antarctica. Methane is good in Greenland, and is used to correlate the two regions since it is essentially well mixed in the atmosphere. David]

    Comment by Chris Colose — 12 Dec 2007 @ 9:05 PM

  19. Several points:-
    1. I thought I had posted on this topic yesterday evening (UK) but there’s no sign of it here now. Am I ‘persona non grata’? (or perhaps I just thought I’d hit the post button but hadn’t
    2. David’s response to post #4 is puzzling me. I read ICE’s post as an enquiry as to what specific mechanisms are considered to be initiators of DE-glaciation but David’s response talks about unknown factors reducing CO2 levels in the atmosphere (the opposite to what I had assumed in de-glaciation). Could you clarify please David (& I don’t mind at all being told I’ve misunderstood.)
    3. The substance of my post that I referred to earlier was that I had assumed, from private advice from Gavin some time ago, that de-glaciations (& indeed glaciations) coincided with the different aspects of the Milankovitch cycles. I recently wondered if increased heat from tidal friction losses could be a deep sea warming mechanism here. (The closer the sun gets, the bigger the gravitational effects leading to bigger to tides & therefore bigger frictional heat losses and therefore warming the oceans differently from direct radiation and finally releasing more CO2).
    I raised several questions on this line of thought. For example, haven’t ‘tidal’ heating effects been speculated for warming of some of the gas giants’ moons? Have any specialists looked at this issue? Is there any conceivable geological evidence that could link increasing tide magnitudes to the start of de-glaciations?

    Comment by Bob Clipperton (UK) — 13 Dec 2007 @ 3:44 AM

  20. Just on question:
    Which is the time resolution (in Greenland and in Antartica )?

    Comment by Ayelén — 13 Dec 2007 @ 6:04 AM

  21. RE #17: “Re Mitchell @ 6: “But correlation alone cannot be an argument, can it? How do you explain the lag between temp and CO2? Isn’t this an argument against causation?”

    No, it’s not. Rising CO2 is not the initial cause of interglacials, but rather a feedback to the initial warming caused by increasing solar insolation, as are changes in albedo as the ice retreats. But then this increase in CO2 leads to yet more warming through the greenhouse mechanism, until equilibrium is gradually reached.”

    I suspect that arguments involving feedback loops are intrinsically difficult to understand. Although a quick trawl with Google Scholar failed to find any research specifically on this, the frequency with which the point Mitchell makes is raised, and also the more sophisticated misunderstanding that a positive feedback loop must lead to a runaway acceleration, suggest this. So do comments of colleagues of mine who have involved local communities in the design of models of social-ecological systems. More generally, I suspect that contrarian pseudoscience (AGW denialism, HIV-AIDS denialism, smoking-cancer denialism, “Intelligent Design”) makes systematic, though not necessarily conscious use of this and similar “cognitive illusions”. Other examples in the climate area may include the “Golden mean” fallacy – that where there is disagreement between two groups, the truth is most likely to lie between their positions – the “curvilinear impetus” fallacy (young children, and even many adults, think that if you start a ball rolling through a curved tube, it will continue to curve after leaving the tube – McCloskey, Caramazza and Green (1980), Science 210:1139-41), which may be behind the belief that increased solar forcing before 1950 could still be accelerating temperature change, and belief in the “law of small numbers” (Ch. 2 in Tversky and Kahneman’s “Judgement under uncertainty: Heuristics and Biases”), which leads psychologists, and presumably others, to overestimate the importance of results from small samples.

    Comment by Nick Gotts — 13 Dec 2007 @ 8:25 AM

  22. p.s. I forgot one: the common belief that enough invalid arguments can outweigh a valid one!

    Comment by Nick Gotts — 13 Dec 2007 @ 8:27 AM

  23. Nick Gotts, another trend I’ve seen in denialists is a seeming inability to understand or appreciate inductive science–the fact that if observations A, B, C… all strongly and independently favor hypothesis 1 over hypothesis 2, while observation X could be interpreted weakly favoring hypothesis 2, this does not invalidate hypothesis 2. Indeed, philosophy of science is even kind of weak on its treatment of this situation, since there is no generally accepted treatment of the absolute strength of evidence for a hypothesis, but rather one has to look at its strength relative to other hypotheses. All of this leads scientists to be rather too circumspect in the way they phrase their conclusions.
    Ultimately, though, scientific is the only way I know of that humans can overcome their biases and their poor abilities at assessing risk–both on the high side (e.g. the terrorism threat in post 9/11 USA) and the low side (e.g. climate change).

    Comment by Ray Ladbury — 13 Dec 2007 @ 9:20 AM

  24. RE #22 (Ray Ladbury) “another trend I’ve seen in denialists is a seeming inability to understand or appreciate inductive science–the fact that if observations A, B, C… all strongly and independently favor hypothesis 1 over hypothesis 2, while observation X could be interpreted weakly favoring hypothesis 2, this does not invalidate hypothesis 2.”

    I think you meant “hypothesis 1″ at the end?

    I believe there’s some evidence that demonstrating and explaining such fallacies can help (I think this was with regard to courtroom situations, but I can’t remember exactly the fallacy involved). On a related point, it may be possible to use logical and textual analysis to identify when opposition to a widely accepted scientific theory or finding (such opposition is of course not necessarily wrong) has become pseudoscience, by looking at the frequency with which such fallacies, and other features such as constantly shifting grounds of objection, accusations of massively concerted fraud, etc., occur.

    Comment by Nick Gotts — 13 Dec 2007 @ 9:44 AM

  25. Re Nick Gotts @20: “I suspect that arguments involving feedback loops are intrinsically difficult to understand.”

    You may well be right, Nick, especially by individuals who tend to see things in a simple one-or-the-other, mutually exclusive way, despite the fact that reality is seldom that simple.

    Comment by Jim Eager — 13 Dec 2007 @ 12:06 PM

  26. Did the sampling give us any information on water vapor? I thought water vapor was a much more significant greenhouse gas than CO2?

    Comment by JH — 13 Dec 2007 @ 12:09 PM

  27. So, why didn’t the ice core diggers get the Nobel instead of Gore?

    Comment by Matt — 13 Dec 2007 @ 12:37 PM

  28. Will the melting of the Ice Sheets have an effect on the orbit of the earth around the sun?

    For that matter does a rising/falling sea levels have an effect on the earth’s orbit (5ft-50ft-200ft-tides)?

    Is the suns radiation still increasing over what it was in the past and do the climate models take this into account?

    Comment by paul m — 13 Dec 2007 @ 1:10 PM

  29. re # 25: These are from air bubbles found in ice samples; I’m not a climate scientist, but I do know that the concentration of water vapor in an air bubble in contact with an ice surface will depend on the *current* temperature of the air bubble and the ice, and not on the conditions when the bubble was formed. (look up “vapor pressure” on Wikipedia.)

    In any case, the maximum possible water content of air drops very quickly as temperature drops, so I don’t think water vapor is an important greenhouse gas *at the poles*.

    Elsewhere on this site you’ll find explanations as to why water vapor is considered a feedback and not a forcing in atmopspheric models.

    Comment by jkga — 13 Dec 2007 @ 1:44 PM

  30. j# 26 Matt: “So, why didn’t the ice core diggers get the Nobel instead of Gore?”

    Perhaps because the “ice core diggers” didn’t go out on the lecture circuit, produce a documentary, and publish a book for a lay audience, in order to raise public awareness of AGW around the world? I’m just guessing, of course.

    Comment by Chuck Booth — 13 Dec 2007 @ 6:12 PM

  31. In the ice core data, the onset of warming periods is always quite rapid – presumably because various positive feedback effects enhance the warming. I have wondered, what puts the lid on the temperature increase? Just as suddenly as the increase in temp and CO2 start, it stops increasing – so some mechanism must come into play with its own set of feedbacks that limit the heating at some point. Can anyone tell me what the current theory on this is?

    Comment by Gary Rondeau — 13 Dec 2007 @ 11:47 PM

  32. Re 26 Matt,
    Gore and the IPCC got a Nobel Peace Prize, not a Nobel Science Prize.

    Comment by Bruce Tabor — 14 Dec 2007 @ 6:56 AM

  33. Re 30 Gary Rondeau,
    I will hazard a guess that the warming ultimately stimulates mechanisms that remove CO2 from the atmosphere – increases in biological activity and rainfall are two that come to mind.

    Comment by Bruce Tabor — 14 Dec 2007 @ 7:01 AM

  34. Gary Rondeau posts:

    [[In the ice core data, the onset of warming periods is always quite rapid - presumably because various positive feedback effects enhance the warming. I have wondered, what puts the lid on the temperature increase? Just as suddenly as the increase in temp and CO2 start, it stops increasing - so some mechanism must come into play with its own set of feedbacks that limit the heating at some point. Can anyone tell me what the current theory on this is?]]

    The temperature increase is a converging series; it comes to a maximum. After that, variations in solar illumination with latitude (the Milankovic cycles) eventually start a cooling trend, and the reactions work in the opposite direction, again coming to a certain point and then stopping.

    Comment by Barton Paul Levenson — 14 Dec 2007 @ 8:03 AM

  35. Gary #30, Most past warming epochs were initiated by mechanisms other than ghg–mainly changes in insolation due to small variations in Earth’s orbit, rotation, tilt, etc. Earth gets more sunlight, so it warms up. As it warms up, ghgs start to be released. There’s no runaway, because the changes (in both insolation and ghg) were rather modest. Remove the increased insolation and Earth has to cool. As it cools, CO2 goes back into the oceans, permafrost, etc. Note that the warming events last thousands of years, so things really aren’t that sudden.

    Comment by Ray Ladbury — 14 Dec 2007 @ 9:27 AM

  36. I have two issues:

    1) Why are CO2 atmospheric levels changing over long term periods (million years) and short term periods? (Short term, before anthropogenic CO2 disturbance.)

    Evidence of past rapid changes (less than 100 years) in CO2 levels seems to provide support for an external forcing function such as solar which can abruptly change planetary temperature. CO2 levels then follow the change in planetary temperature. There is no mechanism presented here that can change CO2 levels in a short term period (less than 100 years) semi cyclically, besides a change in planetary temperature.

    Additional support for a non CO2 climatic driving function is evidence throughout the paleoclimatic record of so called cool periods which occur during periods of high CO2.

    2) The second issue is how low current CO2 levels are based on past levels and the limit of C3 plants. The minimum CO2 level, 175 ppm, reached during glacial maximum is the lowest in the history of the planet. At this level there is evidence of CO2 starvation in leafy planets (C3).

    http://www.ecophys.biology.utah.edu/Labfolks/Ehleringer/Publications/229.pdf

    See figure 1, note current CO2 levels (280 ppm prior to anthropogenic change) are the lowest in 300 million years.

    http://irevues.inist.fr/bitstream/2042/4353/4/CG20

    Comment by William Astley — 14 Dec 2007 @ 1:07 PM

  37. William #34, CO2 is affected by many factors–temperature, volcanism, ecology,… I don’t know what you mean by “semi-cyclically”. A system is either periodic or not. The physics of periodic systems is quite different from that of “quasi-periodic” systems.
    Not sure what point you are trying to make with your second issue. Are you perhaps waxing nostalgic for the Jurassic?

    Comment by Ray Ladbury — 14 Dec 2007 @ 1:46 PM

  38. William Astley writes:

    [[Additional support for a non CO2 climatic driving function is evidence throughout the paleoclimatic record of so called cool periods which occur during periods of high CO2.]]

    You’re dealing with a different time scale. When Earth undergoes a snowball Earth event, CO2 has to build up very high to cause the ice to retreat again. So for a while you have cold temperatures and high CO2. The work of Walker, Kasting, Hays, Lasaga and others on the silicate-carbonate cycle is of interest here. Basically, Earth has a “thermostat” which keeps temperatures in the habitable range most, though not all, of the time.

    Comment by Barton Paul Levenson — 14 Dec 2007 @ 2:39 PM

  39. Ray #33, I’m not claiming that the warming periods are “runaway” events, just that the general waveform looks a lot like a relaxation oscillator to this electrical engineer. The “synchronization” may come from solar/orbital forcing, but the dynamic of the temperature is not anything like those quasi sinusoidal functions. The main nonlinear effect that I can see is just T^4 radiation finally beating out the GHGs that evolve during the heating epoch, but that doesn’t seem like enough to account for the dramatic change in slope of the temperature and CO2 histories at the end of warming episodes. I’m still looking for a good explanation.

    Comment by Gary Rondeau — 14 Dec 2007 @ 11:11 PM

  40. Gary, there are many nonlinear effects and many feedbacks. First, the orbital variations that affect insolation are periodic. You have damping from the thermal reservoir of the oceans (quite complicated with multiple layers exchanging mass and heat on different timescales). You have feedbacks–water evaporation, GHG emission from oceans and melting permafrost, changes in albedo as ice melts and vegetation changes, and so on. Remember that we have much better resolution on the temperature than on the CO2, and that even then, the resolution is, at best, decades. Also, the driver in most of these cycles is insolation–reduce the driver and the system responds rapidly, just as would your oscillator if you reduced voltage.

    Comment by Ray Ladbury — 15 Dec 2007 @ 8:30 AM

  41. In reply to Ray Lamburt’s #35

    William #34, CO2 is affected by many factors–temperature, volcanism, ecology,… I don’t know what you mean by “semi-cyclically”. A system is either periodic or not. The physics of periodic systems is quite different from that of “quasi-periodic” systems.

    Ray, check the attached paper, figure 1. What is causing the abrupt changes in CO2?

    Do the drops in atmospheric CO2 resemble a saw tooth? Is saw tooth like semi-periodic? What is causing that pattern?

    Glacial/interglacial variations in atmospheric carbon dioxide, by Sigman & Boyle

    http://geoweb.princeton.edu/people/faculty/sigman/paperpdfs/Sigman00Nature.pdf

    In reply to Barton Paul Levenson’s #36

    “The work of Walker, Kasting, Hays, Lasaga and others on the silicate-carbonate cycle is of interest here. Basically, Earth has a “thermostat” which keeps temperatures in the habitable range most, though not all, of the time.”

    Barton, The CO2 control device seems to be broken.

    What is missing in this discussion is how low CO2 levels are now and during glacial maximum. During the glacial period roughly a 1/3 of the tropical forest is converted to grass land. Because of CO2 starvation C3 plants (leafy plants as opposed to C4 plants, grasses.) die and are placed by grasses. There is a 10 times increase in dust deposited in the Greenland ice sheet layers during the glacial period which indicates an increase in desertification.

    It is difficult even to explain why CO2 reached such low levels in the glacial maximum. The attached article explains the problem. Sigman & Boyle posit a massive increase in atmospheric dust enables iron deficient regions of the ocean to remove additional CO2 from the atmosphere.

    Excerpt from the above paper:

    “With currently forested or vegetated regions covered under kilometres of ice, an increase in the extent of deserts, apparent conversion of tropical forest to grassland, and exposure of organic-rich sediments on continental shelves, it seems likely that the continental reservoir of organic carbon decreased (My comment: 500 Pg of land based carbon moved to the oceans, in addition to the draw of atmospheric carbon. See paper for details.) during the last ice age, contributing CO2 to the ocean/atmosphere system”

    Comment by William Astley — 15 Dec 2007 @ 3:50 PM

  42. > What is missing in this discussion is how low CO2 levels are now

    How low do you think the CO2 level is now compared to

    >during glacial maximum

    would you give us the numbers you think are correct and your source?

    Comment by Hank Roberts — 15 Dec 2007 @ 4:11 PM

  43. William Astley (39) — To put ‘abrupt’ in perspective, consider the Petit et al. paper on the NOAA Paleoclimatology web pages regarding the Vostok ice core data. Indeed, look at just the 3390 years leading to the CO2 maximum of the Eem, the glacial termination just previous to the one we live during. In this 3390 years, atmospheric CO2 rose from 240.4 ppmv to 287.1 ppmv during the 150 years or so of maximum temperature (via proxy) in the ice core record.

    This delta of 46.7 ppmv is about the same as that which has occurred since around 1973, a period only one-hundredth as long as in the ‘abrupt’ paleorecord.

    Comment by David B. Benson — 15 Dec 2007 @ 4:58 PM

  44. Oh, and have you looked up the recent work on iron dust?
    Try here:
    http://apps.isiknowledge.com/CEL/CIW.cgi?&CustomersID=Highwire&Func=Links&ImgLogo=http%3A%2F%2Fimages.isiknowledge.com%2FImages%2FLinks%2FWOK3%2Ftbretpub.gif&PointOfEntry=CitingArticles&PublisherID=Highwire&ReturnLink=http%3A%2F%2Fwww.sciencemag.org%2Fcgi%2Fcontent%2Fshort%2F294%2F5541%2F309&ServiceName=TransferToWos&ServiceUser=Links&UT=000171601400023&e=.udfgsdHmQejR6EpKfhJzYW0..L5aih5Wu9J0AXV_K4q0qu8RQQQo2xLLdpcsGZ

    Comment by Hank Roberts — 15 Dec 2007 @ 5:09 PM

  45. Oops. The link in #42 expires.
    For iron fertilization, go to any recent published work, then
    – click the ‘related’ and ‘cited by’ links or the like
    to track the research forward to contemporary studies. Short answer, it’s s quite uncertain whether there was a lot of iron fertilization during the dry/dusty/windy periods in the glacial cycles, so reason to be skeptical whether it will work as geoengineering.
    Try here, for example, as a starting point for such searching:
    http://www.sciencemag.org/cgi/content/short/294/5541/309

    Comment by Hank Roberts — 15 Dec 2007 @ 7:38 PM

  46. In reply to Hank Robert’s #40

    “What is missing in this discussion is how low CO2 levels are now”
    How low do you think the CO2 level is now compared to >”during glacial maximum”

    & David Benson’s #41
    “This delta of 46.7 ppmv is about the same as that which has occurred since around 1973, a period only one-hundredth as long as in the ‘abrupt’ paleorecord.”

    We have different climatic change concerns.

    I am concerned about global cooling and climatic stability. See for example the follow paper figure 2 d (dust in the ice). The ice house period cycles appear to be increasing in severity.

    http://www.esf.org/fileadmin/be_user/research_areas/LESC/Documents/nature02599.pdf

    Or see figure 1 in the attached which provides a proxy record of planetary temperature over the last 3 million years. It appears that as the planet has become colder the climate has become unstable (larger cycles?).

    http://www.agu.org/pubs/sample_articles/cr/2002PA000791/2002PA000791.pdf

    My concern is that there is proxy evidence that would indicate planetary temperature can be low when CO2 levels are high. I am concerned increasing CO2 levels will not warm the planet which I believe is the opposite of your concern.

    175 ppm is very low from the standpoint of C3 plants. 340 ppm is not high from the standpoint of past CO2 levels, say over the last 300 MMyrs, typically significantly above 1000 ppm. For example CO2 ranged from 2000 ppm to 3000 ppm, 50 MM to 60 MM yr, from this paper. (figure 3).

    http://www.nature.com/nature/journal/v406/n6797/abs/406695a0.html

    Comment by William Astley — 15 Dec 2007 @ 10:41 PM

  47. William Astley (#39) wrote:

    Barton, The CO2 control device seems to be broken.

    It’s actually just a little slow on the uptake…

    Comment by Timothy Chase — 16 Dec 2007 @ 12:35 AM

  48. William, not sure what your point is. The ice and temperature peaks are sharper than the CO2 peaks. Look at the abscissa on that graph–each of those points is at least decades. Yes, understanding CO2 uptake during cold periods is interesting, but not really relevent to the current epoch. The real changes in CO2 took place hundreds of millions of years ago when the carbon became sequestered in the petroleum deposits and coal beds–and now we are releasing it into the atmosphere again. So in many ways, the paleoclimate of the past 400000 years is less relevant than the paleoclimate of hundreds of millions of years ago. The thing is, the sun was much weaker then, so climatically, we’re in a different regime entirely.

    Comment by Ray Ladbury — 16 Dec 2007 @ 8:22 AM

  49. Worth a read if you can get to a library, or hunt down the information elsewhere; this article’s behind a paywall:

    Is the biofuel dream over?
    New Scientist (subscription), UK – Dec 14, 2007 – Filter
    Can biofuels help save our planet from a climate catastrophe? Farmers and fuel companies certainly seem to think so, but fresh doubts have arisen …

    Someone’s finally done the math on this. Meanwhile the agriculture lobby has gone hog-wild in the US Congress and gotten everything they asked for, calling it ‘energy’ instead of ‘agriculture’ subsidy.

    Comment by Hank Roberts — 16 Dec 2007 @ 12:03 PM

  50. William Astley – shape of the Glacials/Inter-Glacials.

    In addition to the other points above:

    In “Climate Change and Trace Gases”, pages 1932-1934, Hansen et al put forth arguments for the rapidity of melt vs, the slowness of the freeze process. It takes a long time to build multi year ice that can on average withstand “weather” so as to carry the glacial front forward on a millenial basis. But one hot spring/summer can knock it back rapidly. However note that on pages 1929-1930 they explain how GHGs have to be invoked to explain the gross magnitude of the observed temperature trend. PDF of Hansen et al available here: http://pubs.giss.nasa.gov/abstracts/2007/Hansen_etal_2.html

    Mangled into a simple form…

    The initial forcing is just a small variance of forcing at high lattitudes – Milankovitch. Alone that can’t explain the resultant temerature excursion.

    That initial forcing is first amplified by ice sheet extent, which increase the amount of incoming solar reflected back out to space.

    Then once the oceans have warmed/cooled and atmospheric CO2 has increased/decreased, that implied change in radiative forcing amplifies the temperature change further.

    However because ice sheets melt fast, and form slow. And ice sheet extent change (implying albedo change) is the first main driver, there’s an imposed time asymetry to the resultant output wave form – i.e. it’s a saw-tooth wave.

    Well that’s what this amateur reader understands (numerous non-critical-to-first-order caveats and details excluded).

    Comment by CobblyWorlds — 16 Dec 2007 @ 2:28 PM

  51. Regarding iron fertilization of the oceans, etc…

    At this point I am certainly at least willing to investigate the possibility of using iron to increase algae growth for the purpose of reducing atmospheric CO2. But there are also some fairly significant worries with regard to this. Algae produces toxins which could make its way into aquifers (something we are already worried about), and when large algae blooms die, we see them absorb a great deal of oxygen from the surrounding water, creating dead zones that last for months.

    We are already inadvertently encouraging their growth as the result of fertilizer runoff from agriculture, and coastal dead zones are expected to grow simply as the result of global warming. Land warms more rapidly than ocean, and this is changing the ocean currents as the result of changes to atmospheric circulation. This latter process is what is responsible for the growing dead zone off the coast of Oregon which has been expanding into Washington State waters recently. Then there is the issue of what dead zones encourage to grow below the oxycline.

    I would also consider the flotilla of reflective satellites or injecting aerosols into the stratosphere where they will be more long-lived since they won’t be flushed by the next rain — but each of these carries with it their own problems. The sort of global dimming which would be involved I believe results in increased drought — and due to the fact that it is dimming, it will tend to reduce agricultural production. And to counterbalance increasing levels of greenhouse gases, it must increase over time.

    Then there is the possibility of sequestering carbon by means of the production of agrichar/biochar. This is something that I am quite interested in as this will tend to increase agricultural production. However, I have heard that this also results in the production of carcinogens. Not sure how serious this is, though. Something I will want to investigate as time permits.

    Anyway, at this point, I am willing to consider anything — as long as we are willing to consider the potential implications of any “solution,” stop-gap or otherwise.

    Comment by Timothy Chase — 16 Dec 2007 @ 4:06 PM

  52. Not sure under which topic to add this link, the story entitled Ocean’s Growing Acidity Alarms Scientists

    http://www.commondreams.org/archive/2007/12/16/5852/

    which concludes with
    Though cuts in carbon dioxide and other greenhouse-gas emissions might slow or reverse global warming, scientist say it could take thousands of years or longer to reverse the increased acidity of the oceans.

    “For all practical purposes this is permanent,” Emerson said. “That’s not true of temperature. But with ocean acidification the time scales are long.”

    to ask to what extent this is accurate. Are they referring to the deep ocean, with millenial time scales?

    [Response: Actually, the lifetime of anthropogenic CO2 in the atmosphere is indeed measured in millennia, as is the warming to be generated by it. See my very first realclimate post on this topic. The acidification of the ocean also will last for millennia. David]

    Comment by David B. Benson — 16 Dec 2007 @ 4:26 PM

  53. In reply to Ray Ladbury’s #45.

    “William, not sure what your point is. The ice and temperature peaks are sharper than the CO2 peaks. Look at the abscissa on that graph–each of those points is at least decades. Yes, understanding CO2 uptake during cold periods is interesting, but not really relevent to the current epoch.”

    Ray, to me those graphs indicate something (not the amount of CO2 in the atmosphere) is causing the rapid temperature changes. As CO2 levels in the atmosphere follows planetary temperature, it is not clear to me how to determine what portion of the total planetary temperature change is due to the change in CO2 level as compared to other forcing functions.

    This is my problem. CO2 has been less than 500 ppm for the last 24 MM years. See “Atmospheric carbon dioxide over the past 60 million years by Pearson and Palmer. “

    http://www.nature.com/nature/journal/v406/n6797/abs/406695a0.html

    Yet as per figure 1 in the next paper, the planetary has only started to cycle 3 million years ago. What is causing the changing pattern in figure 1 in this paper? The climatic cycles seem to becoming greater, the cold glacial periods more sever and longer.

    Comment by William Astley — 16 Dec 2007 @ 8:58 PM

  54. CobbyWorld #50

    Re: Hanson’s “Paper Climate Change and Trace Gases:”

    CobbyWorld: I do not understand Hanson’s logic. When the planet is warmer there appears to be a strong and consistent negative feedback mechanism (clouds) that resist a change in planetary temperature (warmer or colder).

    http://pubs.giss.nasa.gov/abstracts/2007/Hansen_etal_2.html

    In a control system, a strong positive feedback makes the system unstable.

    When the planet cools to the point that ice sheets form and the ocean freezes the high albedo of the ice sheets and the ice on the ocean causes the planet to cool further (positive feedback). The feedback mechanism is only positive when the planet has cooled to the point that ice sheets form. Look at figure 1 (in the below linked paper) which shows inferred planetary temperature over the last 3 million years.

    To me the graph, figure 1, indicates that the climate was stable when the planet has warmer and became unstable when the planet cooled to the point that ice sheets formed in the Northern Hemisphere. The climatic cycle seems to becoming more extreme.

    http://www.maureenraymo.com/2003_Raymo+Nisancioglu.pdf

    What am I missing?

    Comment by William Astley — 17 Dec 2007 @ 1:43 PM

  55. Mr. Astley, you write:

    > there appears to be a strong and consistent negative
    > feedback mechanism (clouds) that resist a change

    You appear to be citing Hansen’s paper for this. But Hansen doesn’t say that anywhere in that paper.

    And the word “cloud” doesn’t appear in the Raymo paper anywhere at all. So again where do you get this?

    Near as I can tell the IPCC is still right that the effect of clouds is still very indefinite, some reflect, some absorb depending on height and density.
    Recent work here:
    http://www.ingentaconnect.com/content/mksg/teb/2007/00000059/00000004/art00008

    What’s your source for that statement?

    Hansen writes:

    “The unusual stability of the Earth’s climate during the Holocene is probably due to the fact that the Earth has been warm enough to keep ice sheets off North America and Asia, but not warm enough to cause disintegration of the Greenland or Antarctic ice sheets
    …. indications of accelerating change on West Antarctica and Greenland (see below) indicate that the period of stability is over.”

    Hansen’s talking about albedo — ice and water, not clouds.

    Comment by Hank Roberts — 17 Dec 2007 @ 2:21 PM

  56. re #53

    “Yet as per figure 1 in the next paper, the planetary has only started to cycle 3 million years ago. What is causing the changing pattern in figure 1 in this paper? The climatic cycles seem to becoming greater, the cold glacial periods more sever and longer.”

    Are you sure you posted the correct paper, this doesn’t seem to refer to the fig I’m looking at?
    Regarding the changing pattern 3million years ago, that’s about when the atlantic and pacific were separated by the isthmus of panama which would have led to major changes in ocean circulation.

    “Editors’ Choice: Highlights of the recent literature
    The formation of the Isthmus of Panama about 3 million years ago (Ma), a fairly small event in terms of plate tectonics, had dramatic effects on evolution, ocean circulation, and Earth’s climate. Previously isolated North and South American land faunas mixed, and the separation of Atlantic and Pacific waters imposed changes in ocean circulation. One hypothesis is that these changes in ocean circulation triggered the ice ages; the onset of severe Northern Hemisphere glaciation was about 2.5 Ma. Long-term changes in ocean circulation can be monitored using neodynium (Nd) and lead (Pb) isotopes, which reflect the regional geology of exposed continental rocks bordering ocean basins. Thus, different waters will have different isotopic compositions, so their mixing and circulation can be resolved.
    Frank et al. and Reynolds et al. analyzed Nd and Pb isotopes from several ferromanganese crusts in the Atlantic and Pacific oceans and showed that the amount of water being exchanged through the Panama gateway waned noticeably before about 5 Ma, as the Isthmus began to form. This implies that the major effects on ocean circulation occurred considerably before glaciation increased. These records, along with new records of Nd isotopes from foraminifera preserved in sediments from near the Labrador Sea, reported by Vance and Burton, also show that formation of the ice sheets in North America and Eurasia increased erosion dramatically during the past 2 million years. — BH

    Geology 27, 1147 (1999); Earth Planet. Sci. Lett. 173, 381 (1999); Earth Planet. Sci. Lett. 173, 365 (1999).”

    Comment by Phil. Felton — 17 Dec 2007 @ 2:32 PM

  57. William Astley (54) — I am but an amateur here, but I’ll opine that you are only missing what paleoclimatologists are: a sufficiently complete understanding of the drivers and responses of climate change.

    However, I believe you misrepresent figure 1 of the Ramo & Nisancioglu paper. As I read it, the figure indicates the presence of varying amounts of ice volume for the entire past 3 million years. Indeed, it suggests that the warmest interglacials have only occured in the past 475,000 years, other than perhaps at the beginning of the interval being studied.

    Comment by David B. Benson — 17 Dec 2007 @ 3:01 PM

  58. In reply to Phil. Felton #56

    The O18/O16 ratio (see figure 1, Raymo’s paper) in the paper linked to in my comment #54 is directly proportional to ice sheet temperature. Attached is a link to a Wikipedia article that has converted the O18/O16 ratio to inferred temperature on the ice sheet.

    http://en.wikipedia.org/wiki/Image:Vostok-ice-core-petit.png

    Each of those dips in temperature corresponds to a glacial cycle. That last glacial cycle is called the Wisconsin, as the North American ice sheet came down into the state of Wisconsin.

    This is map (also from Wikipedia) that shows the extent of the ice sheet, during the last glacial maximum. Note the vegetation difference in North America. Canada, no vegetation, as Canada is covered by an ice sheet. Central US the vegetation is tundra.

    http://en.wikipedia.org/wiki/Image:Last_glacial_vegetation_map.png

    In reply to Hank Robert #55

    Quote from Hanson’s paper: “The unusual stability of the Earth’s climate during the Holocene is probably due to the fact that the Earth has been warm enough to keep ice sheets off North America and Asia, but not warm enough to cause disintegration of the Greenland or Antarctic ice sheets …. indications of accelerating change on West Antarctica and Greenland (see below) indicate that the period of stability is over.” …

    ”Hanks comment, concerning what Hanson’s paper: Hansen’s talking about albedo — ice and water, not clouds.”

    Hank, the Holocene climate is stable because it is warm and Hanson does not talk about clouds. Yes I agree with that statement. I do not however agree that the Holocene climate will continue to remain stable.

    I believe some researchers have hypothesized that the trigger which brings on the glacial phase is an increase in planetary cloud cover due to a solar cycle change, which causes a drop in planetary temperature which causes snow to fall in regions that have high winter precipitation that now have rain in the winter months.

    Do you understand what my concern is?

    Comment by William Astley — 17 Dec 2007 @ 8:05 PM

  59. > I believe some researchers have hypothesized

    I understand you believe that, but I don’t know whose work you’re talking about. Can you quote from the research, or cite to the research?

    If not, where do you get your belief that some researchers have hypothesized this? I’d like to look at where you find this stated.

    Comment by Hank Roberts — 17 Dec 2007 @ 9:01 PM

  60. William Astley (58) — If your concern is a stade (massive ice sheets) occuring anytime ‘soon’, then there is a definite reply: Not for about 20,000 years. Orbital forcing of stade waxing and waning is firmly supported by the paleorecord; the physics of the entire process is moderately well understood. In particular, orbital forcings can be precisely calculated for millions of years into both the past and future. The earliest a stade could form is about 20,000 years from now, with a considerably better chance at about 50,000 years from now.

    Comment by David B. Benson — 18 Dec 2007 @ 5:40 PM

  61. In reply to David B. Benson’s #60.

    I do not understand your comment. I thought the paleoclimatic data shows interglacial periods ending fairly abruptly, saw tooth step down, rather than a smooth gradual reduction in temperature. (see figure 1 Raymo’s paper, comment #61.)

    Also, I believe solar insolation is currently the same as it was during the last glacial maximum.

    The earth is currently farthest from the sun in June and closest to the sun in December. Due to orbital eccentricity the summers are colder and winters are warmer, because of orbital eccentricity. This is opposite to the condition at the termination of the last glacial cycle.

    Orbital precission (the axis of the earth moves in a circle like a top, with a period of about 20kyr.) changes the timing of the year where the earth is at apogee and perigee of its orbit around the sun. 20,000 years ago when the ice sheets melted the earth was closest to the sun in June and farthest in December. 20kry years ago, the summers where warmer and winters colder, than they are currently.

    The earth’s tilt is now 23.5 degree, as opposed to its maximum tilt of 24.5 degrees.(Minimum is 22 degrees. I believe the orbital tilt was around 24 degrees when the ice sheets melted. The obliquity cycle is 41kyr.).

    I believe colder summers and warmer winters in the critical latitude of 65N, is the condition for the start of a glacial period.

    Comment by William Astley — 19 Dec 2007 @ 12:40 AM

  62. William Astley, thinking a new ice age imminent, posts:

    [[I believe colder summers and warmer winters in the critical latitude of 65N, is the condition for the start of a glacial period.]]

    Why don’t you actually work out the matrix math which interprets the Milankovic cycles and see when the next ice age should start? Everybody who has gets 20-50,000 years from now.

    Comment by Barton Paul Levenson — 19 Dec 2007 @ 9:25 AM

  63. Mr. Astley, you write:

    > I thought the paleoclimatic data shows interglacial periods
    > ending fairly abruptly, saw tooth step down

    You see a ‘saw tooth step’ down, but the ‘up’ side of the event looks like a vertical line, on that very compressed chart.

    Look at a more expanded picture — just the most recent 450kyears — of that same ice age time sequence: http://www.globalwarmingart.com/images/f/f8/Ice_Age_Temperature.png

    You can see that the ‘saw tooth step down’ is the slow cooling over many more tens of thousands of years than the much faster warming event, each time.

    Comment by Hank Roberts — 19 Dec 2007 @ 11:12 AM

  64. In reply to Barton Paul Leveson #61 & Hank Roberts #63

    Hank & B.P.L. I do not understand your comments. Look at Raymo’s paper’s figure 1 at say zoom 400. Where are the long, stable interglacial periods in that record? What is causing that sharp pattern?

    http://www.agu.org/pubs/sample_articles/cr/2002PA000791/2002PA000791.pdf

    I believe most climatic researchers believe the saw tooth abrupt changes in the climatic record are real. For example, from this review paper:

    Sudden climate transitions during the Quaternary

    http://www.esd.ornl.gov/projects/qen/transit.html

    “Until a few decades ago it was generally thought that all large-scale global and regional climate changes occurred gradually over a timescale of many centuries or millennia, scarcely perceptible during a human lifetime. The tendency of climate to change relatively suddenly has been one of the most surprising outcomes of the study of earth history, specifically the last 150,000 years (e.g., Taylor et al., 1993). Some and possibly most large climate changes (involving, for example, a regional change in mean annual temperature of several degrees Celsius) occurred at most on a timescale of a few centuries, sometimes decades, and perhaps even just a few years.”
    “According to the marine records, the Eemian interglacial ended with a rapid cooling event about 110,000 years ago (e.g., Imbrie et al., 1984; Martinson et al., 1987), which also shows up in ice cores and pollen records from across Eurasia. From a relatively high resolution core in the North Atlantic. Adkins et al. (1997) suggested that the final cooling event took less than 400 years, and it might have been much more rapid.”
    I thought there was series of abrupt cooling events throughout the climatic record. (i.e. The Eemian cooling is not an isolated event.) For example, I believe the Younger Dryas

    Comment by William Astley — 19 Dec 2007 @ 12:34 PM

  65. William Astley, if figure 1 in Raymo’s paper is 4 inches long on your screen, then every mm is 3000 years. The “rapid” changes discussed by Adams et al. in your ORNL reference are taking place on a timescale ~10x that of the current warming epoch. Rapid paleoclimatic change epochs are important. They may not provide much guidance for the current epoch.

    Comment by Ray Ladbury — 19 Dec 2007 @ 1:47 PM

  66. William Astley (various posts) — The Eemian interglacial ended rather abruptly. The climactic optimum was 134,000 years ago and it was over by 131,000 years ago. (Do note that the ‘autumal’ phase lasted 3000 years! Abrupt, as I said.)

    The Holocene, on the other hand, is one of the long interglacials, lasting about 28,000 years from so-called Holocene Climatic Optimimum until the next possible stade.

    The interactions of the two main periods of the orbital forcing just happen to be that way just now. But if you look back aways in the paleorecord, you’ll see there was a previous long interglacial. (It might be Termination 4, I don’t recall with certainty.)

    Comment by David B. Benson — 19 Dec 2007 @ 2:46 PM

  67. William Astley (64) — The ORNL review paper you provided a link to appears to have be written in 1998. Since then, more has been learned.

    In my opinion, that paper over-emphasies the similarities of the Holocene to the Eem. For example, in the Petite et al. work on the Vostok ice core, there is a period of about 330 years during the ‘spring’ of the Eem, before the climatic optimum, when the temperature measured by the ice core proxy dropped about 2 degrees Celcius and then recovered. I, at least, know of nothing comperable in the Antarctic ice core records for the Holocene.

    Since that review paper, other data has been collected and interpreted. A recent example is the discovery that (almost surely) the Younger Dryas was caused by a comet striking North America (and also some of Europe and Siberia). Others question the extent to which Greenland ‘sudden warming’ applies to regions other than perhaps northern Europe.

    Still, thank you for the link. The paper was interesting even if now a bit dated.

    [Response: The ORNL paper is indeed dated, but I think you have a mistaken impression of the likelihood of the comet hypothesis being correct. The evidence is very shakey for an impact and the chain of inference linking an impact to climate change is even shakier. There's been some serious science done on this subject but still I'd give it no more than a 10% chance of being correct, and that's generous --raypierre]

    Comment by David B. Benson — 19 Dec 2007 @ 6:34 PM

  68. Raypierre (reponse to 67) — Thank you. My (amateur) reading of the evidence for a comet impact is that it is fairly good. Linking this to climate change is merely good agreements on the dates. I’ll refrain from writing about this connection until well established, if ever.

    And I certainly wish you, and the other contributors here on Real Science, best of the season! :-)

    Comment by David B. Benson — 19 Dec 2007 @ 7:04 PM

  69. In reply to David Benson’s #66

    “The Holocene, on the other hand, is one of the long interglacials, lasting about 28,000 years from so-called Holocene Climatic Optimimum until the next possible stade.”

    I could not find any papers that support an extended interglacial period. The analysis and data, I could find supports the statement that the duration of the interglacial period has in the past been around 12kyr.

    Does anyone have more information concerning the duration of interglacials? How long is the Holocene interglacial expected to last?

    This paper states that the length of the interglacial period is determined by what ever is causing the millennial variability in the climatic record. (Rapid increases and decreases, of planetary temperature.)

    “The Duration of Forest Stages in Southern Europe and Interglacial Climate Variability” by Tzedakis et al.

    http://www.sciencemag.org/cgi/content/abstract/sci;1102398v1

    “What emerges is that, although the broad timing of interglacials is consistent with orbital theory, their specific duration may be dictated by millennial variability. This complicates the prediction of the natural duration of interglacials, at least until the origin of this climate variability is understood.”

    Comment:
    1. Where the interglacial duration is asserted to be longer than 12kyr, the interglacial temperature appears to have not reached typical maximum. (Cycle amplitude is capped, as if the millennial forcing function straddled an orbital cycle.)
    2. The following is a link to Adam’s paper that discussions sudden temperature changes in the Quaternary.

    http://ethomas.web.wesleyan.edu/adamsetal99.pdf

    [Response: I wrote a paper about the onset of the next ice age, and the impact of fossil fuel CO2 on that prospect. You can find it here. We basically concluded that the solar insolation forcing in the NH summer is just grazing the trigger insolation that historically has been correlated with descent into glaciation, so it's too close to call for the natural world this time around. The next such cold snap in the orbital forcing is about 50,000 years from now. Fossil fuel CO2, because it hangs around in the atmosphere for so long, has to potential to keep the Earth from glaciating, we concluded, for hundreds of thousands of years. The last time the Earth's orbit was as circular as it becoming now was isotope stage 11, about 400 kyr ago. That was a long interglacial interval, 30 or 50 kyr I think. David]

    Comment by William Astley — 20 Dec 2007 @ 12:07 PM

  70. William Astley (69) — Here is a link wherein one can find that some of the interglacials were quite long:

    http://en.wikipedia.org/wiki/Timeline_of_glaciation

    but further study (on your part) of MIS 11 and 13 is probably warrented.

    The Archer & Ganopolski paper which David provided a link in his reply is very clear and I recommend it. It is from that paper that I estimated that the Holocene would last about 28,000 years, baring AGW.

    The Adams et al. paper appears to be another over-emphazising the similarity of the Eem and the Holocene, IMO. Nonetheless I’ll attempt to find time to read the two links you provided.

    Comment by David B. Benson — 21 Dec 2007 @ 3:10 PM

  71. Re: #67 #68 — Here is a link to the PNAS paper regarding a North American ET impact 12,900 years ago:

    http://www.pnas.org/cgi/content/abstract/0706977104v1

    pdf file of full paper:

    http://www.pnas.org/cgi/reprint/0706977104v1

    Comment by David B. Benson — 22 Dec 2007 @ 7:36 PM

  72. David, you said:
    “One could imagine a world in which CO2 had no impact on climate, although if you buy that Dick Lindzen has a bridge he wants to sell you. In such a world, it could be that the correlation between CO2 and temperature since 650 kyr was just a coincidence, Mother Nature playing a cruel joke, and maybe in that case a little more data would cause the spurious correlation to start to unravel. That didn’t happen. CO2 continues to be high in warm times and low in cold times.”

    It looks like one simple logical possibility continues to escape your attention: there is no need for T to depend on CO2 for the correlation to take place. It is sufficient that CO2(t) is a time-delayed function of temperature. Therefore, there is no need to invoke “Nature jokes” or “spurious coincidence” to deal with T->CO2 correlation.

    Regards,
    – Al Tekhasski

    Comment by Al Tekhasski — 24 Dec 2007 @ 2:42 AM

  73. Al Tekhasski,
    Well, except there are some paleoclimatic warming events where CO2 seems to actually coincide with the warming. And then there’s all that pesky physics that says increasing CO2 in the atmosphere of a body that radiates in the IR will increase temperature. And there’s all the evidence that CO2 now going into the atmosphere is from a fossil source. But, hypothetically, if you wanted to ignore all the evidence, sure.

    Comment by Ray Ladbury — 24 Dec 2007 @ 7:59 AM

  74. Well, there certainly should be SOME exceptions in an inherently chaotic signal. However, there are plenty of quasi-regular events such as deglaciations. After EACH deglaciation, and when global temperatures are already on decline for a good thousand years, the CO2 concentrations “seems” to continue rising according to ice proxies. Every time. This “seems” to defy the whole CO2-induced catastrophic warming theory. It does seem to me that this is the evidence that you wanted to ignore, sure.

    About that pesky physics… Any PhD in physical sciences seems to know that the whole physics is based on ability to make a distinction between a main effect, and secondary-order effects, which can be estimated and neglected. Obviously, one can find some physics and study an effect of moonlight on growth of telegraph poles. So what?

    Speaking about main effects, you probably know that the OLR curve matches absorbed radiation at the height of approximately 0.6 bar, according to Ray Pierrehumbert book. Interestingly, this is about half way up to tropopause. But wouldn’t you find it coincidental that this is exactly the height of an atmospheric layer that carries about 95% of water vapor?

    Merry X-mas,
    – Alexei

    Comment by Al Tekhasski — 24 Dec 2007 @ 7:21 PM

  75. Well, Al, this PhD in physical sciences learned that one has to consider all of the contributing factors that are significant in the problem. And yes, water vapor is one of them, but would you really expect a factor that varies on a timescale of days to produce >20 years of warming? And in most past warming epochs, CO2 wasn’t the initiator, but rather kicked in after some warming had occurred. This epoch is different from most in a lot of ways. Did you have some specific question or point you wanted to make, or are elliptic references all we can expect. Have a happy holiday, Ray

    Comment by Ray Ladbury — 24 Dec 2007 @ 9:52 PM

  76. Uh, Al, where did you get “Any PhD in physical sciences seems to know that the whole physics [??] is based on ability to make a distinction between a main effect, and secondary-order effects, which can be estimated and neglected.” That seems really oversimplified.

    Do you understand coupled variables? Does it make sense to you that the climate system is such that an increase in temperature might lead to an increase in CO2, or an increase in CO2 might cause an increase in temperature? And, in fact whichever one is increased by an external driver, the other will follow, with positive feedbacks then playing out? You are one of several who keep positing mysteries that any first-year student of differential equations should undertand. The idea that between any two variable in a physical system, only one can be the cause and the oather the effect is plainly simplistic.

    Comment by Ron Taylor — 24 Dec 2007 @ 10:15 PM

  77. Alexei posts:

    [[After EACH deglaciation, and when global temperatures are already on decline for a good thousand years, the CO2 concentrations “seems” to continue rising according to ice proxies. Every time. This “seems” to defy the whole CO2-induced catastrophic warming theory]]

    It does nothing of the kind. Yes, in a natural deglaciation, temperature rises before CO2 does, although the added CO2 then amplifies the warming. But that is not what’s happening now. For 200 years carbon dioxide has led temperature.

    In a natural deglaciation, the carbon dioxide comes from warming oceans. In the present global warming, carbon dioxide is coming from fossil fuels. We know by the isotope signal.

    Your argument is like saying, “People have died naturally for thousands of years, so this guy with his body on the guillotine and his head in the basket must have died naturally.”

    Comment by Barton Paul Levenson — 25 Dec 2007 @ 6:43 AM

  78. RE #72 & “there is no need for T to depend on CO2 for the correlation to take place. It is sufficient that CO2(t) is a time-delayed function of temperature.”

    I, for one, am very concerned that warming increases CO2, since we are in a state of warming now. But T increasing CO2 doesn’t prove in any way at all that C02 doesn’t increase T. And that is the real issue with which people living in the world should be concerned, that given the evidence(and physics)-based hypothesis that C02 increases T, can we prove at the 99% level that it does not increase T. If not, then we need to reduce GHG emissions like crazy, esp since we all agree T increases CO2. I.e., we need to avoid the false negative on this most dangerous situation.

    One problem with Western analytic, linear thinking is that we often fail to see all the interconnections, or the whole picture. It’s like my relative who could take the clock apart, but couldn’t put it back together again.

    Comment by Lynn Vincentnathan — 25 Dec 2007 @ 9:09 AM

  79. Al Tekhasski (764) wrote: After EACH deglaciation, and when global temperatures are already on decline for a good thousand years, the CO2 concentrations “seems” to continue rising according to ice proxies. Every time.

    Not so. I copied the Petite et al. Vostock temperature and CO2 data from the NOAA Paleoclimate web site for the dates around the climatic optimum of the Eemial interglacial (termination 2). I sorted the two data sets together by date. This makes it completely plain that the maximum of the CO2 measurements is during the 150 years or so of maximum temperature.

    Comment by David B. Benson — 25 Dec 2007 @ 3:46 PM

  80. Ray asks: “would you really expect a factor that varies on a timescale of days to produce >20 years of warming?”

    It is a very confused question. First, water vapor persisted in the Earth atmosphere for billion of years. Second, no matter how fast it varies, it always persists here or there, and therefore maintains the GHE on average. Third, maybe the 20-year part of your question is exactly a hint that greenhouse gases are hardly the cause of any warming (if any at all)?

    Comment by Al Tekhasski — 25 Dec 2007 @ 7:05 PM

  81. David, we must be looking at different data. Look again:

    http://www1.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/vostok/deutnat.txt
    http://www1.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/vostok/co2nat.txt

    Dump all into Excel, make charts with proper scaling, and please inspect, say, the period of 250 to 200 kyBP. Keep in mind that the time resolution of CO2 is 1500 years on average in this data set, so it would be hard to nail peaks if they are less than a millennium apart. The counter-trends are all over the place.

    Comment by Al Tekhasski — 25 Dec 2007 @ 7:51 PM

  82. See also:
    http://scienceblogs.com/stoat/2007/05/on_the_co2t_lag_again.php#comments
    http://www.cosis.net/members/journals/df/article.php?a_id=5439

    Comment by Hank Roberts — 25 Dec 2007 @ 9:07 PM

  83. Alexei says: “Keep in mind that the time resolution of CO2 is 1500 years on average in this data set, so it would be hard to nail peaks if they are less than a millennium apart.”

    Yup, Alexei, that would be a good thing to keep in mind. Why don’t you do that? And again, without a consistent trend in H20 vapor, how does it produce a sustained 20 year rise? OTOH, CO2 persists for hundreds to thousands of years.

    So, Alexei, which is it? On the one hand you’re trying to blame the warming on water vapor. On the other hand you’re saying that it can’t be greenhouse gasses. You know, you’re not going to convince many people if you keep changing your story like that.

    How about you posit a cause for the sustained >20 year warming trend we’re experiencing, ‘kay? But keep in mind that it has to warm the poles more than the tropics. It has to warm things at night more than during the day. And so on. Sure sounds like a greenhouse mechanism to me?

    Comment by Ray Ladbury — 26 Dec 2007 @ 8:21 AM

  84. RE #80 & “water vapor persisted in the Earth atmosphere for billion of years”

    From what I understand WV molecules only stay in the atmosphere a few days, so there is a constant infusion of new water molecules (it’s a feedback of other forcings). It’s sort of like seeing that the rate suicide remains fairly constant year to year, but it’s obviously not the same people committing suicide each year.

    As for CO2 molecules — whether they be released into the atmosphere due to the warming melting permafrost and ocean hydrates, or people driving cars, etc. — they stay in the atmosphere a lot longer, a portion staying up even up to 100,000. See http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last

    So, though CO2 is certainly a feedback from the warming, it has the longevity in the atmosphere to be a forcing, whereas WV does not.

    I hope this helps.

    Comment by Lynn Vincentnathan — 26 Dec 2007 @ 10:31 AM

  85. Speaking about forcings v feebacks & responses, I’m thinking there should be some calcuation of how many people we are killing via GW (deaths per xxx tons of GHG emissions), and I think we should include farmer suicides due to GW-enhanced drought as well, and other less direct deaths at the end of GW causal chains. It should also include all the deaths over the entire lifetime of the GHGs emitted today (not just over the next 100 years). We need some ballpark figures on this. It could be done in a multiple “scenario” fashion.

    Also, the GHGs emitted for products produced in, say, China, but consumed by someone in another country should be attributed to the consumer, not the manufacturer.

    Comment by Lynn Vincentnathan — 26 Dec 2007 @ 10:46 AM

  86. Re #85: [Also, the GHGs emitted for products produced in, say, China, but consumed by someone in another country should be attributed to the consumer, not the manufacturer.]

    Not entirely. They should be shared: the consumer has a choice whether or not to buy a product, while the manufacturer has choices about the manufacturing process and energy sources.

    It seems as though implementing a carbon tax would do a pretty good job of apportioning the blame fairly.

    Comment by James — 26 Dec 2007 @ 12:49 PM

  87. RE #86, that sounds right, James. It would only be the products actually purchased by the person. Of course, it’s often a dilemma without good choices re the carbon footprint of the product. So the carbon tax would help, or…..it would be great if each product had a carbon footprint code (overseen by some trustworthy group or agency). That way we could choose the more expensive, but less carbon-intensive produce. Although Confucius say, “how can greater carbon emissions decrease product cost?”

    Comment by Lynn Vincentnathan — 26 Dec 2007 @ 1:46 PM

  88. Al Tekhasski (81) — Same data. But I stated the Eemian interglacial. About 128400 ya in the Petit et al. time reckoning. When the CO2 samples are about 300 years apart.

    It only takes the one to disprove your mistaken claim.

    Comment by David B. Benson — 26 Dec 2007 @ 4:42 PM

  89. The beauty of the carbon tax is that it internalizes the societal cost of carbon emissions in the price of every product, so there is no need for complex calculations regarding carbon footprints. See the Carbon Tax Center web site, http://www.carbontax.org, and note that we recommend a revenue-neutral carbon tax, gradually phased in, to provide time for energy consumers to adjust. At least initially, the societal cost of carbon will not be fully internalized in the price of energy products and in the cost of manufacturing and transporting most all products.

    Comment by Dan — 26 Dec 2007 @ 7:08 PM

  90. David, as I mentioned, the CO2 time resolution is too coarse to compare peaks; the actual peak can be missed due to a lost sample. You’d better look at times from 127445 ybp down to 114082 ybp, where CO2 stayed straight flat while T was dropping like a rock, for a good 14000 years. Or if you prefer shorter time scale, look at the period between 126809 and 124571 – when the CO2 rose by 18ppm over 2200 years, while temperatures dropped by 2C.

    And again, like I said before, noise-contaminated (or chaotic) signals exhibit all sorts of behavior when taken over short periods of time, that’s why a mathematically correct technique called “cross-correlation” should be used. And it says that the two signals are shifted by 800 years, and CO2 is lagging. If you apply sufficient smoothing of each data set, you will clearly see counter-trends after each deglaciaion, precisely for those 800 years.

    Comment by Al Tekhasski — 27 Dec 2007 @ 2:44 AM

  91. Ray Ladbury says: “without a consistent trend in H20 vapor, how does it produce a sustained 20 year rise? OTOH, CO2 persists for hundreds to thousands of years.”

    You are drawing far-fetched conclusions from what I said. I didn’t say that water vapor causes (or “produces”) warming. What I tried to communicate is that water vapor, being in abundance, acts as a greenhouse gas and provides quick and effective balancing of incident solar flux (at the surface) and outgoing long-wave radiation (at the altitude of effective radiating level of atmosphere) by quickly developing corresponding moist lapse rate. The point I am trying to convey is that small addition to this dominating mechanism would not change much of a thing. It seems that you are completely fixated on the idea that 0.01% change in concentration of a minor greenhouse gas could be the only reason for climate variation. What happened to your PhD’s philosophy that “one has to consider all of the contributing factors that are significant in the problem”. Could it be possible that you misjudged significance of some other factors, fro example, those “poorly understood cloud formation” mechanisms?

    And why do you keep insisting on the nonsense that CO2 persists for “hundreds to thousands of years” while the half-life of CO2 seems to be close to 5-10 years, kinetically speaking? If you mean statistics of individual molecules, I am sure you could find one or two water molecules that have been in the atmosphere for a million years, if you trust the classical statistical mechanics.

    I am also not sure about poles or night selective warming. So far the surface (and satellite) data are indistinguishable from noise, so any conditional averages can produce any desirable results.

    Comment by Al Tekhasski — 27 Dec 2007 @ 3:09 AM

  92. Alexei, the effect you mention is included in the models. I suggest you familiarize yourself with the physics of absorption, relaxation, radiation, etc. by greenhouse gasses. I suggest you take a look at the “Saturated Gassy Argument” series on this site, and at Spencer Weart’s AIP History of Climate Change. Spencer in particular has a section on why CO2 persists in the atmosphere rather than completely dissolving in the oceans. Every indication is that so far the oceans have taken up only about half of the CO2 emitted by humans–or do you dispute that CO2 is rising as well?
    I would point out that the physics has been verified by both experts in climate science as well as independent panels and organizatins such as the National Academy of Sciences, AAAS, APS, AGU, ACS. Even the American Association of Petroleum Geologists has withdrawn its opposition.

    Comment by Ray Ladbury — 27 Dec 2007 @ 9:07 AM

  93. Al Tekhasski (90) said David, as I mentioned, the CO2 time resolution is too coarse to compare peaks; the actual peak can be missed due to a lost sample.

    There are no lost samples. For the Eem the coincidence of peaks is clear from just the Petit et al. data. When I have the time I’ll also check this occurs for the Eem in the work on the Vostock ice core of the other two groups also on the MOAA Paleoclimatology site.

    However, your use of cross-correlation is deficient. A highly readable recent paper by Hansen et al., Climate change and trace gasses, will enlighten you.

    However, my point remains that you claim that CO2 always lags temperature during deglaciations is false, due to the example of just the Eem. I am sure there are many, many other examples.

    Comment by David B. Benson — 27 Dec 2007 @ 3:03 PM

  94. David says: “my point remains that you claim that CO2 always lags temperature during deglaciations is false, due to the example of just the Eem.”

    I already told you twice, noisy data could have accidental spikes that coincide. It disproves nothing. Comparing raw noisy data using transparencies is a very deficient technique of 18-th century. Advanced technique in computerized 21-th century is cross-correlation.

    About the paper, it looks as a collection of unsubstantiated statements of faith. To start with introductory sentence:
    “Trace atmospheric gases have played a leading role in climate change throughout Earth’s history.” Cross-correlation of Co2 to T from ice cores with CO2 lag of 700 years clearly disproves this opening presumption.

    Or look at the opening in discussion:
    “Earth’s climate is remarkably sensitive to forcings, i.e. imposed changes of the planet’s energy balance.” For the last 100M years I am sure there were many “imposed changes”. Yet abundance of biological species, all having a pretty narrow range of conditions to exist, have successfully survived, procreated, and evolved into rather high forms, even if the CO2 concentrations have been many times higher than today. This clearly defies the scary “remarkable sensitivity” of climate to various “forcings”, and to trace GH gases in particular.

    [edit]

    [Response: The length of time it takes for the ocean carbon pool to respond to climate changes has no bearing on the radiative forcing of GHGs. And the 'remarkable sensitivity' comes directly from the fact that orbital forcings make tiny changes to the net heat balance of the planet (on an annual cycle), and yet drive huge changes in climate. I agree with Hansen here, that is pretty remarkable. If you want to criticise his papers, you need to raise your game. - gavin]

    Comment by Al Tekhasski — 27 Dec 2007 @ 5:30 PM

  95. Al Tekhasski (94) — Part 4 of the linked lectures will explain better than I why your approach is insufficient:

    http://ocw.mit.edu/OcwWeb/Earth–Atmospheric–and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm

    But in particular, analysis by cross-correlation assumes a particularly simple relationship between the two data sets. In your comment #90 you have already given examples which demonstrate that such a simple relationship does not exist.

    While an amateur student of climatology, I know enough by now not to be overly enthralled by such simplicities and misunderstandings such as Cross-correlation of Co2 to T from ice cores with CO2 lag of 700 years clearly disproves this opening presumption. In particular, in the Hansen et al. paper, leading role is to be read as most important.

    In Carl Wunsch’s lectures, Part 4 of the above link, we see

    Because of this tendency for similarity to be perceived, statisticians have developed objective techniques, such as coherence analysis — ­e.g. Priestley, 1982­ to measure the true similarity of records

    Try that with your lag.

    Comment by David B. Benson — 27 Dec 2007 @ 6:55 PM

  96. Re #94: [For the last 100M years I am sure there were many “imposed changes”. Yet abundance of biological species, all having a pretty narrow range of conditions to exist, have successfully survived, procreated, and evolved into rather high forms, even if the CO2 concentrations have been many times higher than today.]

    Something you miss here is the timescale of the changes. Perhaps this is a perspective effect: long-ago times seem compressed, so that a thousand years, or a million, might get squeezed into a single pixel on a graph.

    Life can adapt to any reasonable change if it has time: time either to move to a more suitable environment, or to evolve to better suit the new conditions. We have many, many instances of such adaptations in the fossil record. The problem facing us is that the time available is too short for adaptation. We have examples of similar situations in the fossil record, too: they’re called extinction events.

    Comment by James — 27 Dec 2007 @ 10:51 PM

  97. David, analysis “by cross-correlation” does not assume any particular relationship, it is just one of methods of data analysis. It is just a function of relative shift of two time series, and it gives you an information. The cross-correlation could be a sharp function of timeshift, or could be a broad (or more complex) function, which would suggests more complex relationship between the two functions, that’s it. There are many more ways to analyze relationship between two time series. You have to agree that peak matching is the least sophisticated method of analysis, and cross-correlation is the next level, and so on. Shift of the peak in cross-correlation function means that the “leading term” of CO2 time series is shifted relative to T time series. Where the additional noise comes from, nobody knows so far.
    In any case, this observed shift is sufficient to conclude that on 1000-years time scale the CO2 follows changes in temperature, and therefore cannot play “leading role” in climate changes. The rest is noise, and you are arguing about noise and second-order effects.

    Comment by Al Tekhasski — 27 Dec 2007 @ 11:48 PM

  98. Al, http://www.skepticalscience.com/co2-lags-temperature.htm

    Comment by Hank Roberts — 28 Dec 2007 @ 1:03 AM

  99. I don’t understand the water vapor variances answers; nay, even the question. What does an infrared photon care if a H2O molecule has been there for a long time or just showed up after a different vapor molecule vanished into a liquid? How does the photon even know the history? It seems water vapor maintains a fairly consistent concentration — variable a little by location with minor ups and downs over a day’s/week’s/month’s period. Why is the fact that vapor molecules are replaced with other vapor molecules over a week or two such an AHA! moment for AGW?? What am I missing?

    Comment by Rod B — 28 Dec 2007 @ 1:22 PM

  100. Lynn (85) Slap! Slap! Lynn, get a grip.. [;>)

    Comment by Rod B — 28 Dec 2007 @ 1:25 PM

  101. Rod B. The photon doesn’t care, but the water content of the atmosphere varies considerably over time–varying from

    Comment by Ray Ladbury — 28 Dec 2007 @ 2:11 PM

  102. Al Tekhasski (97) says Where the additional noise comes from, nobody knows so far. But from Spencer Weart’s Discovery of Global Warming (linked on the sidebar):

    New evidence gave a particularly crucial role to changes in CO2 and other greenhouse gases. These changes were apparently driven not just by geochemistry and ocean circulation, but still more by changes in biological activity. And of course the biosphere depended in turn on climate — and not just temperature, but also trickier matters like fertilization of the seas by minerals eroded from glacial era deserts. Further peculiar influences were added to the list of possibilities almost every year. It would take much more study to determine just what combination of effects determined the shape of glacial cycles.

    Al Tekhasski further says … the CO2 follows changes in temperature, and therefore cannot play “leading role” in climate changes. You need to carefully read the Hansen et al. paper about three times so that you understand that currrently, you misunderstand. I pointed out your misunderstanding, yet you (fairly clearly) do not comprehend.

    Also read the Wunsch chapters I provided a link to. But you might do well to begin with Spencer Weart’s Discovery of Global Warming.

    Instead of attempting to make much out of a cross-correlation for which you one time say is an 800 year lag and another time a 700 year lag. (This is a easy parameter estimation problem, to find that lag which maximizes the correlation coefficient.) And you have yet to state what that correlation coefficient is. You ought to do that before claiming any particular significance can be attached to it. Further, you ought to further do some significance testing.

    I am sorry, but so far you have made untrue claims (from which it seems you have retreated to a mere cross-correlation). Then you vastly over-simplify the climate system by treating biological activity, etc., as mere noise. You don’t bother to indicate how good your correlation is. And you don’t seem to have bothered to look at any of the literature.

    I don’t think anybody should take you seriously as it stands.

    Comment by David B. Benson — 28 Dec 2007 @ 3:29 PM

  103. RE #100, I think such ad hominem attacks are unnecessary. You may not be interested in how many people are dying via AGW or will die over its entire course, but I am. And some ballpark attempts at such stats would complement the many economic calculations surrounding GW and its mitigation that most are so focused on.

    Comment by Lynn Vincentnathan — 28 Dec 2007 @ 7:24 PM

  104. Lynn (103), I meant it as a serious but good-natured barb. But since you’re sticking with serious, the analysis you’re quoting is all huff and puff, a little smoke and mirrors, comparable to calculating the number of deaths caused by Big Macs. It’s worthy of an Paul Ehrlich screed but not much else.

    Comment by Rod B — 28 Dec 2007 @ 11:02 PM

  105. We’ll see the statistics eventually.
    For current risks climate isn’t ranked high. Time will tell.

    http://www.cdc.gov/mmwR/preview/mmwrhtml/00001773.htm
    http://wonder.cdc.gov/wonder/prevguid/p0000109/p0000109.asp#head006000000000000

    —-excerpt—
    Clinicians should emphasize the primary prevention of coronary artery disease (CAD) …. investigating behavioral risk factors for CAD such as tobacco use, dietary fat and cholesterol intake, and inadequate physical activity. …

    Coronary artery disease is the leading cause of death in the United States, accounting for about 1.5 million myocardial infarctions and 520,000 deaths each year.
    —end excerpt—-

    That’s why the nutrition information is now published at the burger place, so you can make your own risk decisions, informed.

    Comment by Hank Roberts — 28 Dec 2007 @ 11:46 PM

  106. Dear David, your power of deduction is truly amazing. If you re-read again your citation from the historical overview, it just says exactly what I said (only with some elaboration on possible spectrum of forces that might affect fluctuations of CO2), that “nobody knows so far”.

    Then you say: “you one time say is an 800 year lag and another time a 700 year”. I guess you are not familiar with the fact that timing scale in all ice record is “tuned” to one or another degree. Do you happen to know how accurate it is? More, as far as I remember from appropriate literature, globally-accessed proxy records yield the estimation of time lag as 800 +-600 years. This is the consensus of climatology at this date. Therefore, any number between 200 and 1400 years is as good as 700 or 800, especially for the sake of establishing the causal relationship between two time series. Picking on 100 years is called “nitpicking”.

    You are truly correct that I am simplifying. In science, it is called an analytical approach: consider major signal/effect first, and neglect (for a while) secondary effects. Then include corrections if necessary.

    On the other hand, you say that I neglected biological activity and denigrated it as “noise”. If you are so sensitive to this, I would recommend to use your own recommendation and look into works of C. Wunsch for analysis of what is regular in glaciation cycles, and what is noise. In a particular work,

    http://ocean.mit.edu/~cwunsch/papersonline/milankovitchqsr2004.pdf

    he shows that “the fraction of the record variance attributable to orbital changes never exceeds 20%”, and “all records are consistent with stochastic models of varying complexity”. Similar conclusions have been reached for every available proxy record. In short, almost all the signal in ice data is noise. That’s why I, as you correctly mentioned”, “don’t bother” much.

    Comment by Al Tekhasski — 29 Dec 2007 @ 4:21 AM

  107. Rod B posts:

    [[What does an infrared photon care if a H2O molecule has been there for a long time or just showed up after a different vapor molecule vanished into a liquid? How does the photon even know the history? It seems water vapor maintains a fairly consistent concentration — variable a little by location with minor ups and downs over a day’s/week’s/month’s period. Why is the fact that vapor molecules are replaced with other vapor molecules over a week or two such an AHA! moment for AGW?? What am I missing?]]

    Residence time affects how much we can change something. If we doubled water vapor overnight, nearly all the excess would be gone in less than a month. But carbon dioxide stays in the air for centuries. We can’t affect water vapor (and neither can nearly anything else aside from temperature), but we can affect carbon dioxide.

    Comment by Barton Paul Levenson — 29 Dec 2007 @ 7:23 AM

  108. Well, I’m not so interested in whether I would die from GW, but more how many we are killing. I know this would be exceedingly difficult, even impossible to calculate, even given various parameters. I understand that according to WHO 160,000 per year are dying from GW-induced vector disease spread at present. And they have attributed half the 30,000 heat deaths in Europe the summer of 2003 to GW. I don’t think they are attributing any deaths due to malnutrition and related diseases due to crop failures in part due to GW. And I don’t imagine they are attributing farmer suicides due to crop failues in India or Australia to it. Or a portion of victims of mega-cyclones, storms, floods, and other extreme weather events enhanced by GW and its various effects. Or thinking that it was that last “umph” of the storm that did the killing or greatest damage…the last part mainly enhanced by GW. Or the reduction of people’s finances due to GW harms, that prevent them getting medical attention, leading to earlier deaths.

    And then no one, I’m sure, is calculating how many will be killed in the future from GW-related problems. And since a portion our CO2 emitted today can last in the atmosphere up to 100,000 years, there may be people dying even then from its effects, or other GW effects set into motion earlier, though the population might be greatly reduced by then (assuming worst-case scenario). (Of course, we should also subtract lives saved by GW effects, in any calculation.)

    I’m sure the information will be forthcoming as scientists are better able to calculate these stats in the decades and centuries ahead, but by then it would probably be too late to then start tackling GW more seriously with the vigor required to make a difference, and all we could say is “sorry,” or we wouldn’t even be around to say sorry when the greatest harms from today’s emissions go into effect.

    I guess some reasons I’d like to know, is so I can explain to people the various GW harms in a more thorough way. Some think it’s only the polar bears who will suffer (and some don’t care about the bears if it means reducing their GHGs), or a tiny bit of land loss due to sea rise (some blame victims for building too close to the shore). It’s hard for most to grasp the entire enormity of GW and all its effects.

    An analogy sometimes I use is it’s like shooting bullets up into the air (they actually do that in S. Texas on July 4th), which come down much later and kill people. But that’s not a good analogy, since only rarely a person gets hit and dies, and with GW we know people are dying already, and the death rate would likely increase over time. It’s somewhat more certain than random shootings.

    Comment by Lynn Vincentnathan — 29 Dec 2007 @ 10:08 AM

  109. Barton, thanks. The words often used (to which I was questioning) are like ‘water vapor lasts only a few weeks’ which implies that it can’t be important as a GHG because it is short-lived. Maybe the implication is inadvertent or just poorly worded. I think you are saying that the concentration of water vapor stays, over the long term, relatively constant; and the “half-life” of any particular H2O molecule is completely irrelevant. That I can understand. Is it correct to assume that you also contend (I may or may not agree with, but I’m trying to understand the argument) that, while water vapor is the “strongest” GHG, it does not provide a direct (or at least major) forcing function, as opposed to indirect feedback influence, because a consistent concentration cannot “force” temperature changes? Or am I over simplifying it?

    Comment by Rod B — 29 Dec 2007 @ 2:57 PM

  110. Rod, How do you put more water vapor in the atmosphere and have it stay there? Raise the temperature. This is the reason why H20 is best looked on as a feedback. CO2 on the other hand stays there–as a gas–for a very long time in pretty much whatever quantity we choose to put it into the atmosphere.

    Comment by Ray Ladbury — 29 Dec 2007 @ 3:27 PM

  111. Rod, your question about the distinction between forcing and feedback is answered well by the presentation beginning here:
    http://www.realclimate.org/index.php/archives/2006/08/climate-feedbacks/

    —briefest possible excerpt—-
    it is important to distinguish between the two. A radiative forcing results from changes that are external to the climate system and may be either natural or anthropogenic in origin. For example, anthropogenic emissions of CO2, changes in solar flux, and the reflection of sunlight from volcanic aerosols are all examples of radiative forcings. A radiative forcing initiates a change in climate that is distinct from the system’s internal variability. A radiative feedback, on the other hand, arises from the response of the climate to either external forcing or internal variability.
    —-end excerpt—-

    My little snippet isn’t enough to fully answer you, but the full posting and links Dr. Soden provide make this pretty clear.

    Short answer on water vapor: the level of water vapor in the atmosphere can’t be controlled by human activity, it’s going to do what it’s going to do. Fossil fuel use is controllable by choices.

    Comment by Hank Roberts — 29 Dec 2007 @ 3:29 PM

  112. Lynn (108), I agree that GW, if it proceeds as predicted by some, will eventually — sometime between next month and next millennia — cause much human suffering and death. But that’s about as far as scientific accuracy allows. The problem is that this scientific assessment does not create desired responses from the populace: it’s (maybe) too far in the future and too indefinite to cause a reaction. So the next political step is to conjecture to the demon level, make everything sound more precise, and surround it in sophisticated-sounding scientific jargon — granted well-intentioned and not fraudulent — to wake up the people to the danger. The WHO has some secret science and understanding that they can fairly accurately predict of the people that died during one summer in Europe, how many died from excessive heat and how much of that excessive heat was the result of global-scaled warming due to increases in CO2?? (Would that have been last year’s increase or maybe last decade’s??) Gimme a break.

    You go on to say, “….I don’t think they are attributing any deaths due to malnutrition and related diseases due to crop failures in part due to GW. And I don’t imagine they are attributing farmer suicides due to crop failures in India or Australia to it. Or a portion of victims of mega-cyclones, storms, floods, and other extreme weather events enhanced by GW and its various effects. Or thinking that it was that last “umph” of the storm that did the killing or greatest damage…the last part mainly enhanced by GW. Or the reduction of people’s finances due to GW harms, that prevent them getting medical attention, leading to earlier deaths….”

    Give them a little more time and a little more head count and, without a doubt, they will. Why? Because they must to get the desired reaction and call to action. And this is true for nearly everything big that government/society wishes to change. I understand that and, in fact, fully support it, so long as I am fully convinced of the necessity.

    I am not (yet?) convinced of the GW scenario. I understand you are and might fully support all of the above assessments. And I fully understand and accept your belief and support for that, and respect your passionate concern. But it’s like claiming 3000 SIDS death from second-hand smoke (they do) or 22,376 cardiac deaths due specifically to eating Big Macs (they’re not there yet but give ‘em time.) It ain’t science; and it ain’t accurate.

    Comment by Rod B — 29 Dec 2007 @ 3:52 PM

  113. Rod asks:
    “while water vapor is the “strongest” GHG, it does not provide a direct (or at least major) forcing function, as opposed to indirect feedback influence, because a consistent concentration cannot “force” temperature changes?”

    In daily operation of the atmosphere, water vapor and temperature field are dynamically coupled, meaning that the temperature and vapor mutually adjust to each other on hourly-daily-weekly time scale through interaction on surface boundary, and via condensation into clouds or rains. In climatology, they call this coupling as “feedback”, which has very little to do with known technical terminology, and creates a lot of confusion. The “forcing” created by water vapor (as a GHG agent) must be calculated from models of general circulation, and is initially unknown. Obviously, temperature is not a solo factor that determines water vapor fluxes. For example, sea surface contamination may vastly reduce supply of vapor into air. Or extent of sea-ice coverage. Or deforestation. Therefore, it is possible that other processes could “force” temperature drifts via GH effect from water vapor, and possibly stronger than the weak background effects from trace gases.

    Comment by Al Tekhasski — 29 Dec 2007 @ 4:48 PM

  114. Lynn says: “Or the reduction of people’s finances due to GW harms, that prevent them getting medical attention, leading to earlier deaths.”

    Wouldn’t the carbon tax vastly decrease people finances by eventually taxing every ptoduct on the market? The whole AGW scare is already affecting gasoline prices, which reduces my ability to pay for medical attention and quality food. Is this what you are advocating?

    Comment by Al Tekhasski — 29 Dec 2007 @ 5:23 PM

  115. Al Tekhasski (106) — Thank you for the link to the Wunsch 2004 paper. That saved me having to hunt it down today.

    The paper is quite good, with regard to the weakness of orbital forcings. However, a further analysis via random walks seems desirable. For example, consider a one-dimensional random walk with reflecting barriers as crudely approximating the longer temperature records. Feller (1968) is the book I have which treats this case, where the transition probablity to the left is p and to the right is q = (1-p), except at the reflecting boundaries. The main point to note is that various statistics depend upon the ratio p/q. Now suppose that orbital forcing slightly varies p and hence q. This is then magnified in the ratio. So it is certainly possible to set up a simple model in which climate variablity is treated as random and yet orbital forcing drives the general nature of the record. In such a model I would suspect that the power spectral estimates would look like those in the Wunsch paper.

    Climate variability is not noise, in the traditional sense. Even the Wunsch paper puts “noise” in quotes. I only object to this term as misleading, not to models which contain random components.

    “Do you happen to know how accurate it is?” Yes. But first of all, not all records are orbitally tuned, but ice core records are perforce tuned one way or the other to turn the known depth into an approximate time scale. For example Barnola et al., analyzing the Vostok ice core, set the CO2 optimum of the Eem at 136.5 kya while Petit et al. set it at 128.4 kya. New results firmly date the temperature maximum of the Eem at 135 kya (unless it is 134 kya, I can’t find my source just now.) Given this, the dates in those two works (and also in Fischer et al.) need further adjusting.

    My understanding of the 800 +/- 600 year lag is from the onset of a major deglaciation until the CO2 begins to rise, not for the entire deglaciation nor for the entire record. Hansen et al. provides more information. In particular, any number between 200 and 1400 years is not equally good. Try doing some reading.

    But most important, the physics of the relationship between global warming (so-called greenhouse) gases and temperature is soundly understood. What is not is all the sources of climate variability nor, yet, the extent to which such can be understood. But in any case, from the physics, there is no surprise in why and how temperature and CO2 closely track. Hansen et al. provides the energetics of why this must occur. Try doing some reading.

    Comment by David B. Benson — 29 Dec 2007 @ 6:23 PM

  116. Re #114: [Wouldn’t the carbon tax vastly decrease people finances by eventually taxing every ptoduct on the market?]

    No, because all the carbon tax plans (that I’ve seen, at least) specifically make the tax revenue neutral. That is, it either replaces some existing tax, such as sales taxes or VAT, or the money collected gets rebated to the people (much like Alaska does with oil revenues). Thus there’s no net effect on people’s finances, though of course there are individual winners – those who figure out ways to reduce their carbon footprint – and losers. But then that’s the whole point, to give people a financial incentive to reduce their emissions.

    Comment by James — 29 Dec 2007 @ 10:37 PM

  117. Hank, Al, et al: thanks.

    Comment by Rod B — 30 Dec 2007 @ 11:07 PM

  118. RE #112 & “The WHO has some secret science and understanding that they can fairly accurately predict of the people that died during one summer in Europe”

    One of the factors that has a GW signature on it was that the death rate was greatly enhanced due to the nights not cooling off much, giving people a chance to recouperate from the heat stress during the day. In a non-GW world, therefore, a similar heatwave would not have killed as many people. And then again, it is that last bit of heat, and heat during the night, that does the person in, that part which is most attributable to GW. They might not have added that consideration into the calculation.

    Not to mention that science is way too conservative in such estimates. I’d like a ball park figure from a false-negative avoiding (medical) perspective, not a false-positive avoiding (scientific) perspective. Just for my own person sense of what might be going on, and what to expect from the future. Not at the level of scientific certainty or of evidence for criminal conviction or even civil case win (preponderance of evidence).

    Comment by Lynn Vincentnathan — 31 Dec 2007 @ 3:09 PM

  119. William Astley (69) — The Adams et al. paper discusses a cooling event about 8.2 kya, seen in the Greenland ice core record. This event led to the abandonment of agriculture on the Anatolian plateau, and possibly elesewhere. The event appears to be contemporaneous with the supereruption of Kurile (now a lake) and so the pluvian/super-pluvian eruption may have triggered the cold interval of about 200 years.

    The paper also remarks on a strong arid event about 4000 years ago “across northern Africa and southern Asia.” This event brought Mesopotamia’s first empire, the Akkadian, to an end in warfare and the distruction of Ur III.

    Something similar happened to the Mayans, according to Jared Diamond. If you wish to worry, worry about the effects of both drought and flooding. Both seem to be happening now.

    Comment by David B. Benson — 31 Dec 2007 @ 3:31 PM

  120. Lynn (118), you say “…..I’d like a ball park figure from a false-negative avoiding (medical) perspective, not a false-positive avoiding (scientific) perspective….”

    I don’t fault that. I just say the self-assured and near arrogant estimates of epidemiological stuff with this looseness is not accurate — pretty much a SWAG. But for one with your background and interest to take that wild estimate with a “100% margin of error” and nonetheless say ‘just possibly something might be there…maybe, and I’d better keep my eyes on it’ is perfectly proper (IMO) from even a scientific viewpoint. There’s nothing unscientific about following hunches, especially if those hunches could be highly leveraged, meaning potential for extraordinary effect if proven correct, as GW is. I’m simply bothered with taking a WAG, however “confident” the WAGer is, and dressing it up in glittering accuracy to try to prove something. The old bury ‘em with stats and math — and don’t worry about reality as long as there are piles and piles of numbers — until they succumb.

    Comment by Rod B — 1 Jan 2008 @ 2:48 PM

  121. My recalled dates for the Eemian interglacial are wrong by about 10 kya:

    According to one of the studies linked below, the Eemian interglacial lasted from 127.3 kya until 116.5 3 kya with the optimum between 126.4 and 124.1 kya. (All dates +/- 3 kya.) Assuming the maximum temperature exactly in the middle, it was at 125.3 kya.

    There were two periods of sea highstand, at 123 +/- 1 kya and again at 121.5 +/- 1 kya, with a pronounced sea lowstand of 4–10 meters below the maxima during the intervening cold period.

    Note that it appears that the sea highstands come near and after the end of the temperature optimum period, if these datings are to be believed. (These are uranium/thorium isotope ratio dates, so likely to the trustworthy within the stated error bars.)

    http://www.ucm.es/info/estratig/JIG/vol331/JIG_33_1_17_30_munoz.pdf

    http://www.cosis.net/abstracts/EGU2007/10084/EGU2007-J-10084.pdf

    http://boyle.mit.edu/~ed/PDFs/Lehman.pdf

    http://www.cosis.net/abstracts/EGU2007/10084/EGU2007-J-10084.pdf

    Comment by David B. Benson — 1 Jan 2008 @ 6:55 PM

  122. Apologies for the messy format. This is just to demonsttate how difficult it is the obtain precise, world-wide unifrom, dates for events only so long ago as the Eemiam interglacial.

    ——————————————————————————–
    Best estimate Region Highstand Reef (R) Intra-Eemian Age of Intra- Ref.
    maximum value (m) Beach (B) sea-level Eemian sea-
    highstand interval Notch (N) drop? level drop (ka)
    (ka)
    highstand Egyptian
    125-120 coast, NW +6 to +9 R, B Y ~122 s1,s2,s3a
    Red Sea
    highstand South Sinai,
    125-118 N Red Sea +3 to +6 R N s5a
    highstand Eritrean +10 to +19 one ~125 and
    125 ± 7 coast, SW R Y (2x) one younger s6a
    Red Sea (regional uplift) event
    highstand
    124-119.5 Possible
    (small second max. Barbados up to +7 R Y lowstand s7
    at 115-114.5) ~122.5
    >0m: 128-120
    highstand after Western N (but hiatus
    isostatic correction: Australia about +4 R reported5) s8,s9
    ~125-120
    Western
    highstand Australia +
    127-122 global above +2 R N s10
    review
    highstand
    129-120 Bahamas up to +6 R Y ~125 s11
    132-118 ~125 s12
    Bahamas +2 to +6 R, N Y
    130-117 ~121 rescaled (s9)
    ———————————————————————————

    Table S1. Summary of literature-based estimates concerning the timing of the MIS-5e
    maximum highstand interval and the possible presence of interruptions of that maximum
    highstand. The overall apparent age range of the maximum highstand is around 128 until
    119 kyr BP, with an average sea-level position around +4 (-2/+2) m. Within that period, a
    brief erosive event/sea-level drop seems to have occurred around roughly 122 ±1 kyr BP.
    Reference numbers correspond to those in the main text.

    Comment by David B. Benson — 1 Jan 2008 @ 8:45 PM

  123. I will agree with Al Tekhasski that the correlation shown doesn’t prove at all that CO2 concentration lead to temperature changes in the past. The lag between T and CO2 strongly supports the opposite, with temperature changes CAUSING CO2 concentration changes.

    This of course doesn’t mean that an atmospheric CO2 increase cannot cause some warming. It probably does. But it is not demonstrated by those graphics and that correlation, by any means. It is posible that CO2 acted as a positive feedback, as has been stated. But only with those graphics, it is as well possible that it didn’t. You cannot use the correlation to prove your point. No way. You need something different if you want to prove that CO2 leads to temperature changes. So from that point of view, the original post is highly misleading and a bad service to science. The prehistorical data doesn’t prove at all that CO2 lead to temperature changes.

    This said, Al Tekhasski is also wrong to say that, because of the lag, it is imposible for the CO2 to influence the temperatures. No, that also cannot be concluded from those graphs. The graphs only say that temperature changes led to CO2 changes in the past, and doesn’t provide a clue about whether CO2 acted in return as a positive feedback or not. It cannot be concluded from the graphs. IMHO it did, although it is not clear to what extent. Maybe it only led to an aditional 5% or 10% increase of the temperature. Maybe it did as much as 50%. It cannot be concluded from the graphs in any degree.

    Our scientific knowledge on GH effect however doesn’t only rely on these graphs. We know for sure that an increase of CO2 by external causes other than temperature changes, like the human activities, by itself, without considering additional factors like cloud formation, insolation and the like, should cause some warming. This wasn’t the case in the past, because CO2 concentration was mostly led by the temperature. But now we are changing that, and we can expect CO2 to have initiated the process of the temperature change.

    Comment by Nylo — 18 Mar 2008 @ 11:57 AM

Sorry, the comment form is closed at this time.

Close this window.

0.480 Powered by WordPress