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Back to the future

Filed under: — gavin @ 30 April 2008 - (Español)

A few weeks ago I was at a meeting in Cambridge that discussed how (or whether) paleo-climate information can reduce the known uncertainties in future climate simulations.

The uncertainties in the impacts of rising greenhouse gases on multiple systems are significant: the potential impact on ENSO or the overturning circulation in the North Atlantic, probable feedbacks on atmospheric composition (CO2, CH4, N2O, aerosols), the predictability of decadal climate change, global climate sensitivity itself, and perhaps most importantly, what will happen to ice sheets and regional rainfall in a warming climate.

The reason why paleo-climate information may be key in these cases is because all of these climate components have changed in the past. If we can understand why and how those changes occurred then, that might inform our projections of changes in the future. Unfortunately, the simplest use of the record – just going back to a point that had similar conditions to what we expect for the future – doesn’t work very well because there are no good analogs for the perturbations we are making. The world has never before seen such a rapid rise in greenhouse gases with the present-day configuration of the continents and with large amounts of polar ice. So more sophisticated approaches must be developed and this meeting was devoted to examining them.

The first point that can be made is a simple one. If something happened in the past, that means it’s possible! Thus evidence for past climate changes in ENSO, ice sheets and the carbon cycle (for instance) demonstrate quite clearly that these systems are indeed sensitive to external changes. Therefore, assuming that they can’t change in the future would be foolish. This is basic, but not really useful in a practical sense.

All future projections rely on models of some sort. Dominant in the climate issue are the large scale ocean-atmosphere GCMs that were discussed extensively in the latest IPCC report, but other kinds of simpler or more specialised or more conceptual models can also be used. The reason those other models are still useful is that the GCMs are not complete. That is, they do not contain all the possible interactions that we know from the paleo record and modern observations can occur. This is a second point – interactions seen in the record, say between carbon dioxide levels or dust amounts and Milankovitch forcing imply that there are mechanisms that connect them. Those mechanisms may be only imperfectly known, but the paleo-record does highlight the need to quantify these mechanisms for models to be more complete.

The third point, and possibly the most important, is that the paleo-record is useful for model evaluation. All episodes in climate history (in principle) should allow us to quantify how good the models are and how appropriate are our hypotheses for climate change in the past. It’s vital to note the connection though – models embody much data and assumptions about how climate works, but for their climate to change you need a hypothesis – like a change in the Earth’s orbit, or volcanic activity, or solar changes etc. Comparing model simulations to observational data is then a test of the two factors together. Even if the hypothesis is that a change is due to intrinsic variability, a simulation of a model to look for the magnitude of intrinsic changes (possibly due to multiple steady states or similar) is still a test both of the model and the hypothesis. If the test fails, it shows that one or other elements (or both) must be lacking or that the data may be incomplete or mis-interpreted. If it passes, then we a have a self-consistent explanation of the observed change that may, however, not be unique (but it’s a good start!).

But what is the relevance of these tests? What can a successful model of the impacts of a change in the North Atlantic overturning circulation or a shift in the Earth’s orbit really do for future projections? This is where most of the attention is being directed. The key unknown is whether the skill of a model on a paleo-climate question is correlated to the magnitude of change in a scenario. If there is no correlation – i.e. the projections of the models that do well on the paleo-climate test span the same range as the models that did badly, then nothing much has been gained. If however, one could show that the models that did best, for instance at mid-Holocene rainfall changes, systematically gave a different projection, for instance, of greater changes in the Indian Monsoon under increasing GHGs, then we would have reason to weight the different model projections to come up with a revised assessment. Similarly, if an ice sheet model can’t match the rapid melt seen during the deglaciation, then its credibility in projecting future melt rates would/should be lessened.

Unfortunately apart from a few coordinated experiments for the last glacial period and the mid-Holocene (i.e. PMIP) with models that don’t necessarily overlap with those in the AR4 archive, this database of model results and tests just doesn’t exist. Of course, individual models have looked at many various paleo-climate events ranging from the Little Ice Age to the Cretaceous, but this serves mainly as an advance scouting party to determine the lay of the land rather than a full road map. Thus we are faced with two problems – we do not yet know which paleo-climate events are likely to be most useful (though everyone has their ideas), and we do not have the databases that allow you to match the paleo simulations with the future projections.

In looking at the paleo record for useful model tests, there are two classes of problems: what happened at a specific time, or what the response is to a specific forcing or event. The first requires a full description of the different forcings at one time, the second a collection of data over many time periods associated with one forcing. An example of the first approach would be the last glacial maximum where the changes in orbit, greenhouse gases, dust, ice sheets and vegetation (at least) all need to be included. The second class is typified by looking for the response to volcanoes by lumping together all the years after big eruptions. Similar approaches could be developed in the first class for the mid-Pliocene, the 8.2 kyr event, the Eemian (last inter-glacial), early Holocene, the deglaciation, the early Eocene, the PETM, the Little Ice Age etc. and for the second class, orbital forcing, solar forcing, Dansgaard-Oeschger events, Heinrich events etc.

But there is still one element lacking. For most of these cases, our knowledge of changes at these times is fragmentary, spread over dozens to hundreds of papers and subject to multiple interpretations. In short, it’s a mess. The missing element is the work required to pull all of that together and produce a synthesis that can be easily compared to the models. That this synthesis is only rarely done underlines the difficulties involved. To be sure there are good examples – CLIMAP (and its recent update, MARGO) for the LGM ocean temperatures, the vegetation and precipitation databases for the mid-Holocene at PMIP, the spatially resolved temperature patterns over the last few hundred years from multiple proxies, etc. Each of these have been used very successfully in model-data comparisons and have been hugely influential inside and outside the paleo-community.

It may seem odd that this kind of study is not undertaken more often, but there are reasons. Most fundamentally it is because the tools and techniques required for doing good synthesis work are not the same as those for making measurements or for developing models. It could in fact be described as a new kind of science (though in essence it is not new at all) requiring, perhaps, a new kind of scientist. One who is at ease in dealing with the disparate sources of paleo-data and aware of the problems, and yet conscious of what is needed (and why) by modellers. Or additionally modellers who understand what the proxy data depends on and who can build that into the models themselves making for more direct model-data comparisons.

Should the paleo-community therefore increase the emphasis on synthesis and allocate more funds and positions accordingly? This is often a contentious issue since whenever people discuss the need for work to be done to integrate existing information, some will question whether the primacy of new data gathering is being threatened. This meeting was no exception. However, I am convinced that this debate isn’t the zero sum game implied by the argument. On the contrary, synthesising the information from a highly technical field and making it useful for others outside is a fundamental part of increasing respect for the field as a whole and actually increases the size of the pot available in the long term. Yet the lack of appropriately skilled people who can gain the respect of the data gatherers and deliver the ‘value added’ products to the modellers remains a serious obstacle.

Despite the problems and the undoubted challenges in bringing paleo-data/model comparisons up to a new level, it was heartening to see these issues tackled head on. The desire to turn throwaway lines in grant applications into real science was actually quite inspiring – so much so that I should probably stop writing blog posts and get on with it.

The above condensed version of the meeting is heavily influenced by conversations and talks there, particularly with Peter Huybers, Paul Valdes, Eric Wolff and Sandy Harrison among others.

523 Responses to “Back to the future”

  1. 301
    Rod B says:

    Martin (296), now we’re cookin’ with gas (pun intended!) You say, “…but it’s worth very little..”

    We just disagree. I say it explains the actual physical process of surface radiation heating the atmosphere; I think that important in climatology.

    You add, “CO2: crash-emit-absorb-emit to space: atmospheric temperature change (opposite direction, cooling)”

    Good point, and I agree as long as the collision imputes energy to vibration and not translation — which is unlikely but not as unlikely as I initial thought (per Phil and Ray — thanks)

    You say, “(I see you left out emit-to-earth-surface… )”

    Only because I was trying not to boil the ocean (no pun intended) and simply figure this out piece by piece. Though it is significant as it explains how the surface heats up through back-radiation, again a seemingly important (actually damn important) physical process in this GW stuff.

  2. 302
    Al Tekhasski says:

    Ray Labury (#298), that is the difference between a good science and ill science. When confronted with mathematically ill-posed problem, good scentist will evaluate necessary accuracy of measurements and find a limit of applicability of an inverse method (which would be pretty short), and will not draw daunting conclusions out of ill-conceived idea, while the junk scientist would persist in applying non-applicable to support his prejudicial conclusions. Temperature reconstructions from boreholes is one such example. Estimation of “Anthropogenic CO2” from measurements of total DIC is another. And the role of CO2 in global climate change is another one. And, at no surprise, it never works.

  3. 303
    Ray Ladbury says:

    No, Al, a good scientist will figure out to pose the problem differently so that he or she can get something out of it. One reliable guide is not to rely on single sources/types of data. And climate science gives a coherent account of what is going on in a noisy system precisely because it follows such guides.

  4. 304
    Al Tekhasski says:

    Ray Ladbury, I am confused :-) The problem at hand is about detailed climate reconstruction from paleorecords. Does your reply mean that now you agree with me (#292) that the problem is ill-posed, and climate scientists need to find another, different way to validate GCMs?

    [Response: Is it ill-posed that there was an ice age 20,000 years ago? Or that rainfall was greater in the Sahara 6000 years ago? Of course not. Therefore your apparently absolutist point is nonsense. The only issue remaining is one of degree – how much detail can we recover from past climates? That will vary as you go back in time and on the size of signal. But blanket claims that this is impossible are just bogus. – gavin]

  5. 305
    dhogaza says:

    One was review author for one of the working groups for the latest IPCC report, did not dispute the idea that the sun had greater effect on climate than in the models, but simply said that there was no known mechanism so they couldn’t model it

    Uh, pointing out that there is no known mechanism IS disputing the point.

    Politely.

    Apparently too politely, in your case, because you seem to be interpreting the fact that there’s no known mechanism as support for your position that ummm … the KNOWN mechanism by which CO2 forces temp increases is somehow wrong. Because you know in your heart that UNKNOWN mechanisms related to the sun must be the culprit.

  6. 306
    Martin Vermeer says:

    Rod B #301, #296

    I say it explains the actual physical process of surface radiation
    heating the atmosphere; I think that important in climatology.

    Yes, but not until you get past this:

    … per se (NOTHING ELSE happening) has no effect on the temperature of the
    gaseous environment where the CO2 lives

    …so which will it be?

    … I agree as long as the collision imputes energy to
    vibration and not translation — which is unlikely but not as unlikely as
    I initial thought

    You can ballpark these probabilities, as Ray pointed out. LTE, the Maxwell distribution. And compute the population levels for the excited states, knowing only temperature. Under stationarity, the number of collisional excitations will match the number of collisional de-excitations… otherwise the CO2 would be exchanging net heat energy with the non-greenhouse gases.

    Only because I was trying … to … figure this out piece by piece.

    Sure, understood.

  7. 307
    Al Tekhasski says:

    Hey, Gavin, I absolutely would not mind if your model will reproduce glaciation-deglaciation cycles for the last 600,000 years, even if their quasi-period or rate of deglaciations would be slightly off. However, your approach to validation seems to follow the fine principle of climatology – it is good enough when you feel it is good enough. I know you do not believe that global climate is evolving around natural chaotic attractor, but let me ask this: do you have a model of atmosphere dynamics that calculates (not forces) cloud cover that matches current observations to 1% accuracy?

    [Response: The reason talking to you is pretty pointless is because of comments like this. You started above with an interesting point, you pushed it to a nonsensical extreme and then when called on it, you switch the topic to something completely different. This might be your idea of a dialog, but for most people it’s a waste of time. Me included. – gavin]

  8. 308
    Al Tekhasski says:

    Gavin, the distinction between qualitative modeling (as you said, “ice age”, or “rainfall was greater”, all without any quantification) and quantitative prediction is not “nonsensical extreme”. Therefore, I was not “called on it”, nor did I switch to different topic. In case you forgot, various climate “administrations” are pushing _quantitative_ predictions of global temperatures on us, mentioning certain specific numbers. This is the quantitative modeling, and it must conform to quantitative standards. If you consider this distinction as a waste of time, then it just confirms my description of your methodology. Therefore, please respond to my question about cloud cover in #307. This question is critical for quantitative modeling of climate and the role of CO2.

    [Response: No it isn’t. It’s just some arbitrary metric you picked so that you don’t have to address the other issues. This is a thread on paleo-climate, not cloud modelling, and so either stick to the topic or go elsewhere. – gavin]

  9. 309
    Vincent van der Goes says:

    One issue often discussed regarding the climate in the far past is the so-called ordovician glaciation period. In the late Ordovicium, glaciation occured while CO2 levels are said to have been around 4000 ppm. Hearing this confused me. I tried searching for articles about this period, but was confused even further – many sources write about this period, but so far I didn’t find a satisfying explanation of this weird event.

    Could anyone please shed a light on this subject?

  10. 310
    Hank Roberts says:

    Is rainfall a proxy for cloudiness in paleo records?
    I’ve been trying to think of anything that would be.

  11. 311
    Al Tekhasski says:

    No, Gavin, it is not an arbitrary metrics, and not off topic since cloud cover is an important part of a good climate model. How important? Look at the full-spectrum model of atmosphere offered here:
    http://forecast.uchicago.edu/Projects/full_spectrum.html
    You can see that 1.4% change in low cloud cover negates the whole effect of CO2 doubling. Clearly, changes in process of cloud formation are two orders of magnitude more important than changes in CO2. Do you have paleorecords of cloud cover 100,000 years ago, with about 1% accuracy?

    [Response: Of course not. Frankly, we don’t even have that for today’s climate. Thus we can know nothing. Brilliant. I’ll just pack up and go home then….. Seriously though, the issue is to always take the information that you do have and do your best to make sense out of it, not to sit around wishing for perfection. I think there is useful information in paleo-records and I have written many papers exploiting it – it could be done better of course, but it is pretty amusing to hear over and over that something can’t possibly be done when it already is being. You want examples? Try Otto-Bliesner et al (Science, 2006), or Legrande et al (PNAS, 2006) or Schneider von Deimling et al (2005). – gavin]

  12. 312
    David B. Benson says:

    Completely on-topic: I devised an unusual (for me) statistical test to look for fairly short period oscillations (quasi-periodic) in the record of the Holocene central Greenland GISP2 ice core temperatures by Alley. Short period means from 35 to 190 years.

    The method works, in effect, by cutting the entire record into shorter pieces and studying all of those. I found oscillations in the 45–90 year bands in 81–87% of the short periods. For the longer period bands, the oscillations never appear so often.

    I take this 45–90 year band as being the effect of PDO on the central Greenland temperatures.

    [Response: Why? You need to show a) that there is a signature of the PDO at Summit, and b) that this calibrates to the known variations over the instrumental period. Vague associations based on the frequency domain are very unsatisfactory unless you have a really good reason to expect it (i.e the annual cycle, milankovitch frequencies etc.) – gavin]

    Do note the wider band than is usually attributed to the PDO and the fact that about 15% of the time (by this method) it does not appear at all during the Holocene.

  13. 313
    Hank Roberts says:

    Ah, I thought I remembered this. There’s paleo information suggesting increasing clouds and rain may be near the end of the last really fast CO2 increase — a sudden increase in large scale rapid erosion:
    http://ic.ucsc.edu/~jzachos/eart120/readings/Schmitz_Puljate_07.pdf

  14. 314
    David B. Benson says:

    Gavin replied “You need to show a) that there is a signature of the PDO at Summit, and b) that this calibrates to the known variations over the instrumental period.” Summit? Does this mean the location of the GISP2 ice core? Is there a long enough surface temperature record there? (I had thought not.)

    Calibrates? I fear I don’t understand what is expected to calibrate with what.

    Yes, vague associations are indeed unsatisfactory. But since the PDO is supposed to modulate El Nino/La Nina, I thought it ought to show up. It does, sorta. A more thorough study would use a better statistical method and consider several ice cores, not just one.

  15. 315
    Hank Roberts says:

    David, there’s a lot of reading available, e.g.:
    http://adsabs.harvard.edu/abs/2004AGUFMGC44A..04M

  16. 316
    Mike says:

    Ray Ladbury #300 said “Think about this in a logical, linear fashion: CO2 forcing is constrained by multiple (>5), independent lines of evidence. For what you are asserting to be true, all of these constraints would have to be wrong and all in the same way and by about the same amount. How likely do you think that is? … You would also have to come up with a new mechansim for heating the planet that gave rise to a 30 year warming trend. And it needs to explain why the stratosphere is cooling etc.”

    I have explained why they are all wrong in the same way and by the same amount. At some point they all work off the same basic assumption and tailor their parameters to the same observations.

    I personally don’t have to come up with a mechanism. The information given by the IPCC makes it clear that such a mechanism has to exist, but that they don’t know what it is. At some point, someone will no doubt work out what the mechanism is. In the meantime, the IPCC have some data on the effect that the unknown mechanism has, so it is unacceptable for them to simply ignore it.

    If you read my reply to Al Tekhasski below, you will see that a warming influence other than CO2 did indeed operate over the last part of the 20th century. Given that its behaviour tallies better with solar variation than with CO2 levels, it may be a clue to the missing mechanism.

    dhogaza #305 said “Pointing out that there is no known mechanism IS disputing the point”.

    Not so. The point not disputed was that the sun had a greater effect on climate than was allowed for in the models. The fact that there is no known mechanism is not disputed by them or me or anyone else. The statement shows that the sun’s effect was ignored. I discussed this with the last scientist that I referred to before – all the time I’m trying to test my ideas to make sure they are robust or to find the flaws in the them – and he had quite a lot to say about it, including “Just to say we can’t model something cuts no ice with me at all”.

    —–

    Al Tekhasski #311 said “You can see that 1.4% change in low cloud cover negates the whole effect of CO2 doubling”.

    This is confirmed in the IPCC report, para 1.5.2.

    Al and Gavin, we do have global albedo records for the last decade or so, and by proxy for a previous decade or so, and by much weaker proxy back to about 1900. They show that global albedo declined rapidly over the last part of the 20th century. They also show that global albedo has been increasing since then. See http://www.iac.es/galeria/epalle/reprints/Palle_etal_EOS_2006.pdf The final sentence is : “Accounting for such [global albedo] variations in global climate models is essential to understanding and predicting climate change.”.

    There are a number of papers on the subject, from the same stable, and they spell out some of the complexities in interpreting the information and relating it to global temperature etc. For example, high clouds and low clouds have different net climate effect.

  17. 317
    Ray Ladbury says:

    OK, Mike, I have tried to at least get you to learn some of the physics before you take on your crusade against all 150 years of climate science, but you are bound and determined that you, with you, what, 6 months of experience can overturn what physics has built in 150 years. Good luck with that.

  18. 318
    David B. Benson says:

    Hank Roberts (315) — Thanks. Using hint you provided I found this graph

    http://www.ncdc.noaa.gov/paleo/pubs/biondi2001/fig4c-lg.gif

    which seems to give good-enough agreement with my amateur attempt. So this (and some other papers) indeed suggest that the PDO signal ought to show up in GISP2. That’s all I intend to do on this matter.

    It is enough to indicate, to me at least, that paleoclimate data might well be used to further constrain at least some aspects of computerized climate models.

  19. 319
    Hank Roberts says:

    Mike, the Search box (top of page) will save much retyping; for example: http://www.realclimate.org/index.php/archives/2006/02/cloudy-outlook-for-albedo/

  20. 320
    dhogaza says:

    Not so. The point not disputed was that the sun had a greater effect on climate than was allowed for in the models.

    Meanwhile, Leif Svalgaard argues that the models allow for a greater effeoct on climate than is allowed for by real data (and he’s a solar physicist).

    So, apparently, the models must be wrong, because one of the two proofs given above must be true, right?

  21. 321
    Rod B says:

    Martin (306), “……so which will it be?”

    I think we’re pretty close, so to be brief (and repetitive…, sorry): Looking at it stepwise, a photon of energy absorbed into a vibration state of CO2, as a self-contained and unique 1st step, does not alter the classic temperature of that molecule, or of the plethora of molecules in the local environment. This is an important piece of physics as it is one of the many critical individual molecular steps taken toward global atmospheric warming/cooling. Glossing over the pieces, especially if maybe not understood, to get to the end is not sufficiently rigorous and gives AGW a tinge of HPFM; or as the cartoon of the professor explaining his algorithm captions, “and now a miracle happens.” ;-)

  22. 322
    Mike says:

    Ray Ladbury #317. My attention is focussed much more on the modelling error than on the physics. That is why I have been in contact with climate scientists, to make sure I’m getting the science bit right – but more importantly perhaps to make sure that solar variance really was left out of the models. I was at a symposium where scientist A said that the effect of solar variation on the Earth’s climate was heavily underestimated in the IPCC models, probably by a factor of about 4, and scientist B (the IPCC one) confirmed that the full effect had been left out of the IPCC models simply because there was no known mechanism. I emailed this to scientist C (another IPCC one) who replied “Precisely. How do you you include a mechanism that is unknown?”.

    It is not my intention to work out what the mechanism is, that is physics which is not my domain. But the fact that a possibly very important factor has been left out of the models is in the domain of modelling and is worth pursuing. I have pursued it using every avenue that I can think of, and received confirmation from several sources, including the IPCC report itself and scientists associated with the IPCC, that this factor was indeed left out of the models.

    Hank Roberts #319. Thx.

  23. 323
    Mike says:

    Hank Roberts #319. Thx. I had a look at the paper you linked. It certainly makes a case for treating ‘Earthshine’ results with caution.

    There is an interesting graph in the ISCCP paper, Part 1
    http://isccp.giss.nasa.gov/zD2BASICS/B8glbp.anomdevs_t.jpg

    It clearly shows the global cloud cover decreasing from 1995-98 to 1999-01, by what appears to be a climate-significant amount, then putting in and maintaining a small rise to 2007.

    I would suggest that it would be worth investigating this as a possible link to solar variance, since it maps much better to solar activity than to CO2 levels.

    There are three possible non-exclusive links between solar variance and climate that have been mooted, that I am aware of : magnetic field, ultraviolet and clouds. I also couldn’t help noticing that the loss of Arctic ice has been ascribed to winds, and that winds got a mention in I think a RealClimate article as possibly accelerating the paleo cycle when it turned down (I should be able to find the links if wanted).

    I would be interested in keeping an eye on these, if anyone has some relevant links.

  24. 324
    Martin Vermeer says:

    Rod B #321:

    Looking at it stepwise, a photon of energy absorbed into a vibration
    state of CO2, as a self-contained and unique 1st step, does not alter
    the classic temperature of that molecule, …

    No Rod… you’re inventing your own physics here.

    Temperature is defined (simplifying a little) as the average amount of random motion energy per degree of freedom. Defined as an average, you are not really allowed to apply it to a single molecule, but if we apply it anyway, then, yes, absorption of a photon into a vibrational state, exciting that state in a CO2 molecule, raises the temperature of that molecule. Vibration is a form of random molecular motion. It is part of the definition of temperature. (Why do you think this degree of freedom contributes to he specific heat of the gas?)

    …, or of the plethora of
    molecules in the local environment.

    By the time the added energy is equipartitioned, through collisions, with the local environment, that temperature will have gone up too.

  25. 325
    Chris N says:

    Just saw a paper on the GISS website on aerosols. 85% of sulfates are in the NH. Hmmm. No significant warming in SH for the past 30 years where sulfate loading is low and relatively constant. There is warming in the NH, particularly between 1993 and 1998. Sulfate emissions in the NH likely decreased after the 1990 Clean Air Act and the fall of the Former Soviet Union. Coincidence? I think not!

  26. 326

    Mike writes:

    My point is that the models have taken away most of the Sun’s warming, by simply ignoring the evidence, and given it to the CO2 warming, by overestimating ECS.

    We understand your point thoroughly. We just think it’s wrong.

    First of all, for hindcasts the models use the known values of TSI from someone’s compilation (e.g. Lean 2000 or Wang et al. 2004), or the known sunspot counts. For forecasts they can simply impose a reasonable 11 and 22 year cycle.

    Second, and more importantly, the models do NOT take forcing from the solar column and add it into the CO2 column. The CO2 forcing is decided independently of the solar forcing or any other forcing. If you could prove solar had a larger effect, it would NOT prove that CO2 had a smaller effect. It would just mean that some third-party effect had to be countering the CO2.

  27. 327

    Vincent van der Goes posts:

    One issue often discussed regarding the climate in the far past is the so-called ordovician glaciation period. In the late Ordovicium, glaciation occured while CO2 levels are said to have been around 4000 ppm. Hearing this confused me. I tried searching for articles about this period, but was confused even further – many sources write about this period, but so far I didn’t find a satisfying explanation of this weird event.

    Could anyone please shed a light on this subject?

    The “carbonate-silicate cycle” acts as a very-long-term stabilizer of temperature on Earth. CO2 in the atmosphere is drawn down by weathering, but raised by volcanic and metamorphic emission. If the Earth heats up, weathering increases, which draws down CO2. If the Earth cools down, weathering decreases, and CO2 builds up in the atmosphere.

    The control mechanism is not perfect. There have been episodes of widespread glaciation in Earth’s history, some possibly so severe as to have created a “snowball Earth” situation (2300, 800, and 600 million years ago most noticeably). When that happens, the Earth’s albedo is very high, its temperature is very low, and CO2 has to build up to quite high levels before the ice begins to melt back again.

    Thus it is not sufficient to know what the levels of temperature and CO2 were at different times. You must also know the history. CO2 is not the only thing that affects temperature; albedo and cloud cover and solar input and a host of other factors matter as well. Temperature and CO2 correlate well now because none of the other factors are changing substantially.

  28. 328

    Mike posts:

    a warming influence other than CO2 did indeed operate over the last part of the 20th century. Given that its behaviour tallies better with solar variation than with CO2 levels…

    Except that it doesn’t. Sunlight has shown no trend for the past 50 years:

    http://members.aol.com/bpl1960/LeanTSI.html

  29. 329
    Ray Ladbury says:

    Rod B., If you want to apply a stick of dynamite to the log jam that has developed in your mind regarding temperature, energy, degrees of freedom and so on, consider this: In a laser, where you have a population inversion, with more molecules in a high-energy state than in the ground state, the temperature is negative! This makes absolutely no sense if you look on the temperature in terms of average kinetic energy. It makes perfect sense if you look at the physics in terms of the Maxwell distribution. It makes perfect sense if you look at the temperature in terms of the partial of energy wrt entropy. Add more energy, and you will promote even more molecules from the ground to the excited state, so the population is even more inverted. Cogitate on that awhile and hopefully you’ll see that the concept of temperature is a lot more general than simply average KE per dof.

  30. 330
    CobblyWorlds says:

    #325 Chris N,

    If the observed warming is due to a drop in “dimming” then how was it that by 2000 surface insolation had not recovered to 1960s levels according to BSRN & GEBA datasets? i.e ~0.6degC GW as the surface insolation dropped overall….
    Dimming is almost certainly hiding the full impact of CO2 driven warming. For a start check out Wild & Ohmura’s work.

    By the way, the warming carried right on through 1998 which was an outlier. So that doesn’t work either.

    #328 Barton Paul Levinson,
    Lest we forget…
    Neutron Counts (as you know, a proxy for GCRs) http://cr0.izmiran.rssi.ru/clmx/main.htm
    No trend.
    Nothing.
    Nada.
    Zilch.

    #309 Vincent van der Goes,
    It’s been a few years since I read about the Ordovician and CO2, but I’m not sure CO2 was actually high at the time of glaciation:
    http://www.sciencedaily.com/releases/2006/10/061025185539.htm
    If I remember rightly the time resolution of the CO2 proxy record is such that CO2 levels may have been a lot lower than most of the Ordovician, when the glaciation actually happened.

  31. 331
    Mike says:

    Barton Paul Levenson #326 said “We understand your point thoroughly. We just think it’s wrong.”. I’m happy to leave it there. When the IPCC are proved to be absolutely right, I’ll write to you all if you’re still around, and concede.

    Barton Paul Levenson #328 said “Sunlight has shown no trend for the past 50 years”.
    \Well. I would have been happy to leave it there. I wrote it before reading this next post.

    From the Judith Lean data posted (I presume it was Judith Lean):
    1900 1364.458
    2000 1366.674

    That’s an increase of 2.2 W m-2 over the 20th century. (I checked that these years were in kilter with the years nearby, and you can see the trend clearly in the graph).

    The IPCC report Summary for Policymakers says that “the global average net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W m–2”.

    So if I read the figures that you posted correctly, the increase in direct solar irradiance over the 20th century exceeded that claimed for AGGs since 1750.

    But we still haven’t allowed for the multiplier effect in the IPCC report para 1.4.3 : “There is increasingly reliable evidence” that a variation of about 0.2 W m-2 in solar irradiance “could cause surface temperature changes of the order of a few tenths of a degree celsius.”

    Now I know that this whole climate thing is complex. I know that there are disputes about the temperature measurements, that there are very significant time lags, that there are lots of things that don’t behave in a linear manner, that there are things whose effect changes in combination with other things, etc etc etc, so expected effects don’t necessarily show up straight away or at the exact amount expected. [BTW this answers CobblyWorlds #330 too]

    But I think the figures you posted provide extremely strong support for my case.

    The sentence at the end of the item you posted “Therefore, increased sunlight cannot be driving the sharp global warming of the last 30 years.” – was that your comment, or Judith Lean’s?

    PS. Given the importance of the Sun to climate, you would expect that there would be a number of solar physicists on the IPCC team. I have been told that Judith Lean was the only one. Is that right?

    [Response: The mistake you are making is a very common one, and you are in good company in making it, but it is still wrong (take you solar number and multiply by 0.7 and divide by 4. And look up Foukal et al (2006) for a more up-to-date assessment). – gavin]

  32. 332
    Chris N says:

    #330 Cobblyguy,

    To make my contention clear, dimming is lower today than 1960, thus the reason for 2000 to be warmer in NH than in 1960. For some reason, most people assume dimming increases along with CO2 concentration. I contend it has been the opposite: lower CO2 concentration in the past with higher dimming; and higher CO2 concentration today with lower dimming. Also, it resulted in less sea ice reflecting irradiance as a compounding effect. Regarding your other point, the vast majority of the warming occurred between 1993 and 1998 (see post 237 above, and yes there were no error bars provided).

  33. 333
    Rod B says:

    Martin (324), I’ll admit to finding references that say or imply both sides, though most references just ignore the detail we’re discussing — why is anybody’s speculation. A relatively simple reference is in Wikipedia, though I can’t vouch for its authenticity — I presume it is good though less than peer reviewed. Go see http://en.wikipedia.org/wiki/Thermodynamic_temperature

    Or just buy the following brief excerpts: “The thermodynamic temperature of any bulk quantity of a substance (a statistically significant quantity of particles) is directly proportional to the average—or “mean”—kinetic energy of a specific kind of particle motion known as translational motion.”

    “The kinetic energy stored internally in molecules does not contribute to the temperature of a substance (nor to the pressure or volume of gases).”

    Most refer to internal molecular energy as having “characteristic temperature”, which is not “real” (sensory) temperature, just a convenient construct, though can be confusing.

    So, unless and until the radiation absorbed into vibration or rotation modes gets partitioned out to translation, thermodynamic (real) temperature is not changed. And, this precisely (or close enough…) explains and justifies the variance in specific heat — some energy being added to a molecule(s) with zero change in temperature because of that specific delta-E.

  34. 334
    Rod B says:

    ps I think it is “characteristic temperature” that Ray is referencing (329). It is also used in reference to radiation and other stuff. And, BTW, it is a very helpful construct — and can mathematically give you negative temperature — so I’m not refuting it at all. I’m simply talking of “real” “thermodynamic” “sensory” temperature. This is all about global warming and “real temperature” is all that counts here. If the temperature can not be felt by anybody or anything, then global warming is a no-op!

  35. 335
    Rod B says:

    pps and guys who work with “characteristic temperature” just say “temperature” ’cause it’s easier and efficient — they all know of which they speak.

  36. 336
    tamino says:

    Re: #331 (Mike)

    I’d really like an answer to this question: why is it that when BPL states that there’s been no solar increase for 50 years, you reply with estimates 100 years apart?

    Here are some more numbers from Lean:

    1950: 1366.022
    2000: 1366.674

    The difference is 0.652. And as Gavin (correctly) points out, that’s the change in solar irradiance, not climate forcing. You have to divide by 4 (for the sphericity of the earth), then multiply by 0.7 (to account for albedo), which gives 0.114 W/m^2 climate forcing change. That’s only one fourteenth the estimated anthropogenic forcing.

  37. 337
    Hank Roberts says:

    Mike, you’re confusing a slight change in _surface_temperature_ with heating the planet up.

    And you’re confusing effects of the very slight solar variation — a fraction of a watt out of the total some 1300 watts/square meter — with turning up the heat.

    This may affect how and where the winds move a bit. It likely changes the surface temperature. Not temperature of the whole planet. Mixing more cold ocean water with the surface water, for example, by changing wind patterns. Look for a possible connection that fits the magnitude of the energy transfer involved. A small difference can change _how_ the heat moves around on the planet.

    Aug 14, 2007 … north-south position of the atmospheric jet stream …. drives intraseasonal wind variations …
    http://www.pnas.org/cgi/reprint/104/33/13262.pdf

  38. 338

    Rod B #333

    A relatively simple reference is in Wikipedia, though I can’t vouch for its authenticity — I presume it is good though less than peer reviewed. Go see http://en.wikipedia.org/wiki/Thermodynamic_temperature

    “The kinetic energy stored internally in molecules does not contribute to the temperature of a substance (nor to the pressure or volume of gases).”

    OK. This (if not a mistake) differs from the definition of temperature that I learned in school… but note that for LTE in a gas, it is inconsequential.

    Most refer to internal molecular energy as having “characteristic temperature”, which is not “real” (sensory) temperature, just a convenient construct, though can be confusing.

    Well, when using an old-fashioned thermometer, temperature reaches its mercury bob always through linear molecular motion… but such temperature measurement is based on LTE anyway, and meaningless without it.

    I assume that the differences you find between sources are simply due to starting from different definitions. The physics is the same.

    A problem I see with the Wikipedia definition here is that with solids, you’re in a bit of ambiguity trouble. In a molecular solid (ice) you could say that kinetic temperature is defined by the vibrations of the H2O molecules. Now look at salt, NaCl. No molecules. Do you have to look at Na and Cl separately? Or diamond, one gigantic molecule. Why treat the C’s in a diamond separately if you’re not allowed to do the same for the C’s in an organic molecule? This is arbitrary. Needless to say I am unhappy with the Wikipedia definition (if that’s what it is).

    BTW not even Wikipedia is completely unambiguous. It says

    “At its simplest, “temperature” arises from the kinetic energy of the vibrational motions of matter’s particle constituents (molecules, atoms, and subatomic particles).” Would seem to agree with me.

    “The thermodynamic temperature of any bulk quantity of a substance (a statistically significant quantity of particles) is directly proportional to the average—or “mean”—kinetic energy of a specific kind of particle motion known as translational motion.” My emphasis. It does not say “is defined by”. For LTE the statement is correct.

    I like my definitions clean and general. Ray’s definition d(energy)/d(entropy) certainly is, but not very intuitive.

  39. 339

    Rod B #334:

    ps I think it is “characteristic temperature” that Ray is referencing (329).

    Yes. Note that a laser is far from LTE.

    It is also used in reference to radiation and other stuff.

    That’s again a bit different.

    And, BTW, it is a very helpful construct — and can mathematically give you negative temperature — so I’m not refuting it at all. I’m simply talking of “real” “thermodynamic” “sensory” temperature.

    Under LTE they are all the same. Up in the atmosphere, the “sensory” temperature is actually the least interesting of them all… it’s all about interaction with radiation, not with thermometers or with people’s skins :-)

  40. 340
    Vincent van der Goes says:

    RE: 327 (Barton Paul Levenson)

    > The control mechanism is not perfect. There have been episodes of
    > widespread glaciation in Earth’s history, some possibly so severe
    > as to have created a “snowball Earth” situation (2300, 800, and 600
    > million years ago most noticeably). When that happens, the Earth’s
    > albedo is very high, its temperature is very low, and CO2 has to
    > build up to quite high levels before the ice begins to melt back again.

    So albedo is a strong positive feedback, in both directions. However, since the period prior to this glaciation was hot (and CO2 rich), something else than albedo must have initiated the ice age.

    > Thus it is not sufficient to know what the levels of temperature and
    > CO2 were at different times. You must also know the history. CO2 is
    > not the only thing that affects temperature; albedo and cloud cover
    > and solar input and a host of other factors matter as well. Temperature
    > and CO2 correlate well now because none of the other factors are changing
    > substantially.

    Solar input was a little lower back then. And one should also take the geographical position of continents into account. Still, I find it amazing that such factors could have initiated an ice age, when (if) CO2 levels were indeed this high. After all, 4000 ppm is almost four doublings above pre-industrial levels.

    RE: 330 (Cobblyworlds)

    Thanks for the link. Unfortunately, I could not find any quantative estimates in this article on the CO2 levels prior and during the ice age. The source I am relying on now is wikipedia: http://upload.wikimedia.org/wikipedia/commons/7/76/Phanerozoic_Carbon_Dioxide.png
    This information could be outdated or incomplete, of course.

  41. 341
    John Finn says:

    Re: #336

    Here are some more numbers from Lean:

    1950: 1366.022
    2000: 1366.674

    Here are some numbers from GISS

    1944: 0.21
    2000: 0.33

    an increase of just over one tenth of a degree.

    Is it not possible that solar forcing actually has a cumulative effect over time. Now let me think where might it store heat …. what about the oceans??

  42. 342
  43. 343

    Mike posts:

    Barton Paul Levenson #328 said “Sunlight has shown no trend for the past 50 years”.
    \Well. I would have been happy to leave it there. I wrote it before reading this next post.

    From the Judith Lean data posted (I presume it was Judith Lean):
    1900 1364.458
    2000 1366.674

    That’s an increase of 2.2 W m-2 over the 20th century.

    Do you not understand what “the last fifty years” means? What year is it now? What year was Lean’s article published in? How did you get from “the last fifty years” to “the 20th century?”

  44. 344
  45. 345
    Ray Ladbury says:

    John Finn, Gee, if the warming is coming from a source of heat within Earth, how do you get zero warming for 30 years, followed by 30 years of accelerating warming. That seems to me to be a rather tall order.
    The game you are playing here is explaining what we don’t know by what we don’t know. That isn’t what scientists do–they explain the unknown in terms of the known. However, you are free to prove me wrong. Construct a model that hides heat in the oceans for 30 years and then suddenly dumps it into the world we can see.

    Oh, and for extra credit, show me why the greenhouse effect due to CO2 magically stops at 280 ppmv.

  46. 346
    Mike says:

    Gavin’s response to #331 : “take your solar number and multiply by 0.7 and divide by 4”. Of course. I should have checked. Apologies. Lets’s do the arithmetic with the correct numbers :

    1900 1364.458
    2000 1366.674

    That’s an increase of 2.2 W m-2 over the 20th century, multiply by 0.7 and divide by 4 gives 0.385 W m-2.

    Now let’s add in the IPCC report para 1.4.3 : “There is increasingly reliable evidence” that a variation of about 0.2 W m-2 in solar irradiance “could cause surface temperature changes of the order of a few tenths of a degree celsius.”. Now it might not be linear, but we’re probably looking at about double “a few tenths of a degree Celsius”. The total global warming for the 20th century was 0.74 deg C (IPCC).

    That was a lot more than I needed for my case, but I can accept that.

    tarnino #336 said “I’d really like an answer to this question: why is it that when BPL states that there’s been no solar increase for 50 years, you reply with estimates 100 years apart?”.

    I have been referring to the 20th century for quite a long time. Why did BPL suddenly switch to 50 years? Simple, just look at the graph he posted. 50 years was much more convenient for him than the full century. Given that we all agree that short periods are not very relevant in climate discussions, it seems to me that there is merit in working with longer periods when possible.

    Hank Roberts #337 said “Mike, you’re confusing a slight change in _surface_temperature_ with heating the planet up.”. Well, no. I’m referring to the same _global_ surface temperature that the IPCC reference for their ‘global warming’ figures. The slight solar variation you refer to is the same idea as the solar variation I did the sums for above. It looks slight, but as the IPCC points out, there is evidence that it can punch above its weight.

    Thanks for your comments on winds etc, I haven’t looked at the link yet, but I will.

    Vincent van der Goes #340 said “So albedo is a strong positive feedback, in both directions. However, since the period prior to this glaciation was hot (and CO2 rich), something else than albedo must have initiated the ice age.”.

    There is also the possibility that albedo is not a feedback at all. That it operates independently of CO2. That would mean that it definitely is possible that albedo did initiate the ice age. This idea opens up the whole of the paleoclimate cycle to a _much_ simpler explanation than James Hansen’s.

  47. 347
    Jim Eager says:

    “There is also the possibility that albedo is not a feedback at all. That it operates independently of CO2.”

    News Flash: Albedo does operate independently of CO2.

    Albedo change is a feedback to warming or cooling, regardless of the initial cause of that warming or cooling.

    What ever made you think otherwise?

  48. 348
    tamino says:

    Re: #346 (Mike)

    50 years was much more convenient for him than the full century.

    It’s not because 50 years is more convenient. It’s because it’s more relevant. You’re the one who’s choosing time periods because they’re convenient.

  49. 349
    Abbe Mac says:

    Re #340 where Vincent wrote:

    So albedo is a strong positive feedback, in both directions. However, since the period prior to this glaciation was hot (and CO2 rich), something else than albedo must have initiated the ice age.

    The Ordovician glaciation was resticted to the land near the south pole, which would have been cooler than the non-polar regions. This was also during the start of the Caledonian orogens, and the mountain tops could have become snow covered, since at high altitudes there is little water vapour and, although the concentration of CO2 was high, its density would have been much lower in the rarefied atmosphere at high altitude.

    The glaciation possibly coincided with the Trans African mountains passing over the pole, which could have become ice covered just as the Himalayas are today at a lower latitude.

    Albedo is raised, not only by the ice but also by clouds. An ice covered pole would have initiated a polar vortex that would have created a cloud band around the polar region. The cold air flowing out from the ice covered mountains would have under cut the warm marine air coming from the sub-tropics.

    The lesson here is that without the Arctic sea ice there will be no northern polar vortex. The resulting loss of clouds will cause a decrease in planetary albedo and a massive rise in global temperatures.

    HTH,

    Cheers, Alastair.

  50. 350
    CobblyWorlds says:

    #340 Vincent van der Goes,

    I’m fairly sure I have nothing more than you have from Wikipedia.

    Paleo-climate is not my primary interest, and I’m not a scientist, just a former-sceptic turned hobbyist, so don’t take this as “gospel”:

    I noted your implied question “something else than albedo must have initiated the ice age.” Just to make sure, I hope I’m not pointing out the obvious (although obvious is subjective): The reason I posted that article was because the hypothesis discussed is that a tectonic accident (the rise of the Appalacians) exposed rock to weathering, and it was the chemical weathering that used up atmospheric CO2. So the CO2 in the atmosphere was much reduced allowing temperatures to reduce enough for an ice age to start, at which point ice albedo would become a factor. As to what ended it, probably volcanic CO2 possibly in some major event (flood basalt perhaps).

    I’d advise against following the curves in the Wikipedia image too closely. Note that the Royer compilation is a set of spot “samples” of CO2 levels (detail may be lost between samples), with large error bars. And the 30M year filtering just smooths that same data. Futhermore as you can see, the other readings are models. Royer (which is the only actual proxy-based dataset) starts just before the Ordovician so doesn’t help anyway.

    And yes ice-albedo feedback can be a very strong feedback: Over sea, exposing water gives a net gain of the order of +60% increased absorption of the incident solar radiation.
    .

    #332 Chris N,

    To make my contention clear, dimming is lower today than 1960, thus the reason for 2000 to be warmer in NH than in 1960.

    No need to clarify, I understand you.

    But GEBA/BSRN indicate that dimming in the 1960s was less than in 2000. As dimming reduces surface insolation, that’s why I said “insolation had not recovered to 1960s levels”, insolation is incoming solar radiation.

    So what you’re claiming is that the warming is due to an overall drop in solar radiation at the surface!