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The Global Cooling Bet – Part 2

Filed under: — group @ 13 May 2008 - (Italian) (Deutsch) (Español)

Last week we proposed a bet against the “pause in global warming” forecast in Nature by Keenlyside et al. and we promised to present our scientific case later – so here it is.

This is why we do not think that the forecast is robust:

Fig. 4 from Keenlyside et al '08

Figure 4 from Keenlyside et al ’08. The red line shows the observations (HadCRU3 data), the black line a standard IPCC-type scenario (driven by observed forcing up to the year 2000, and by the A1B emission scenario thereafter), and the green dots with bars show individual forecasts with initialised sea surface temperatures. All are given as 10-year averages.

  1. Their figure 4 shows that a standard IPCC-type global warming scenario performs slightly better for global mean temperature for the past 50 years than their new method with initialised sea surface temperatures (see also the correlation numbers given at the top of the panel). That the standard warming scenario performs better is highly remarkable since it has no observed data included. The green curve, which presents a set of individual 10-year forecasts and is not a time series, each time starts again close to the observed climate, because it is initialised with observed sea surface temperatures. So by construction it cannot get too far away, in contrast to the “free” black scenario. Thus you’d expect the green forecasts to perform better than the black scenario. The fact that this is not the case shows that their initialisation technique does not improve the model forecast for global temperature.
  2. Their ‘cooling forecasts’ have not passed a the test for their hindcast period. Global 10-year average temperatures have increased monotonically during the entire time they consider – see their red line. But the method seems to have produced already two false cooling forecasts: one for the decade centered on 1970, and one for the decade centered on 1999.
  3. Their forecast was not only too cold for 1994-2004, but it also looks almost certain to be too cold for 2000-2010. For their forecast for 2000-2010 to be correct, all the remaining months of this period would have to be as cold as January 2008 – which was by far the coldest month in that decade thus far. It would thus require an extreme cooling for the next two-and-a-half years.
  4. Even for European temperatures (their Fig. 3c, not part of our proposed bet), the forecast skill of their method is not impressive. Their method has predicted cooling several times since 1970, yet the European temperatures have increased monotonically since then. Remember the forecasts always start near the red line; almost every single prediction for Europe has turned out to be too cold compared to what actually happened. There therefore appears to be a systematic bias in the forecasts.
  5. One of the key claims of the paper is that the method allows forecasting the behaviour of the meridional overturning circulation (MOC) in the Atlantic. We do not know what the MOC has actually been doing for lack of data, so the authors diagnose the state of the MOC from the sea surface temperatures – to put it simply: a warm northern Atlantic suggests strong MOC, a cool one suggests weak MOC (though it is of course a little more complex). Their method nudges the model’s sea surface temperatures towards the observed ones before the forecast starts. But can this induce the correct MOC response? Suppose the model surface Atlantic is too cold, so this would suggest the MOC is too weak. The model surface temperatures are then nudged warmer. But if you do that, you are making surface waters more buoyant, which tends to weaken the MOC instead of enhancing it! So with this method it seems unlikely to us that one could get the MOC response right. We would be happy to see this tested in a ‘perfect model’ set up, where the SST-restoring was applied to try and get the model forecasts to match a previous simulation (where you know much more information). If it doesn’t work for that case, it won’t work in the real world.
  6. When models are switched over from being driven by observed sea surface temperatures to freely calculating their own sea surface temperatures, they suffer from something called a “coupling shock”. This is extremely hard, perhaps even impossible, to avoid as “perfect model” experiments have shown (e.g. Rahmstorf, Climate Dynamics 1995). This problem presents a formidable challenge for the type of forecast attempted by Keenlyside et al., where just such a “switching over” to free sea surface temperatures occurs at the start of the forecast. In response to the “coupling shock”, a model typically goes through an oscillation of the meridional overturning circulation over the next decades, of the magnitude similar to that seen in the Keenlyside et al simulations. We suspect that this “coupling shock”, which is not a realistic climate variability but a model artifact, could have played an important role in those simulations. One test would be the perfect model set up we mentioned above, or an analysis of the net radiation budget in the restored and free runs – a significant difference there could explain a lot.
  7. To check how the Keenlyside et al. model performs for the MOC, we can look at their skill map in Fig. 1a. This shows blue areas in the Labrador Sea, Greenland-Iceland-Norwegian Sea and in the Gulf Stream region. These blue areas indicate “negative skill” – that means, their data assimilation method makes things worse rather than improving the forecast. These are the critical regions for the MOC, and it indicates that for either of the two reasons 5 and 6, their method is not able to correctly predict the MOC variations. Their method does show skill in some regions though – this is important and useful. However, it might be that this skill comes from the advection of surface temperature anomalies by the mean ocean circulation rather than from variations of the MOC. That would also be a an interesting issue to research in the future.
  8. All climate models used by IPCC, publicly available in the CMIP3 model archive, include intrinsic variability of the MOC as well as tropical Pacific variability or the North Atlantic Oscillation. Some of them also include an estimate of solar variability in the forcing. So in principle, all of these models should show the kind of cooling found by Keenlyside et al. – except these models should show it at a random point in time, not at a specific time. The latter is the innovation sought after by this study. The problem is that the other models show that a cooling of one decadal mean to the next in a reasonable global warming scenario is extremely unlikely and almost never occurs – see yesterday’s post. This suggests that the global cooling forecast by Keenlyside et al. is outside the range of natural variability found in climate models (and probably in the real world, too), and is perhaps an artifact of the initialisation method.

Our assessment could of course be wrong – we had to rely on the published material, while Keenlyside et al. have access to the full model data and have worked with it for months. But the nice thing about this forecast is that within a few years we will know the answer, because these are testable short term predictions which we are happy to see more of.

Why did we propose a bet on this forecast? Mainly because we were concerned by the global media coverage which made it appear as if a coming pause in global warming was almost a given fact, rather than an experimental forecast. This could backfire against the whole climate science community if the forecast turns out to be wrong. Even today, the fact that a few scientists predicted a global cooling in the 1970s is still used to undermine the credibility of climate science, even though at the time it was just a small minority of scientists making such claims and they never convinced many of their peers. If different groups of scientists have a public bet running on this, this will signal to the public that this forecast is not a widely supported consensus of the climate science community, in contrast to the IPCC reports (about which we are in complete agreement with Keenlyside and his colleagues). Some media reports even suggested that the IPCC scenarios were now superseded by this “improved” forecast.

Framing this in the form of a bet also helps to clarify what exactly was forecast and what data would falsify this forecast. This was not entirely clear to us just from the paper and it took us some correspondence with the authors to find out. It also allows the authors to say: wait, this is not how we meant the forecast, but we would bet on a modified forecast as follows… By the way, we are happy to negotiate what to bet about – we’re not doing this to make money. We’d be happy to bet about, say, a donation to a project to preserve the rain forest, or retiring a hundred tons of CO2 from the European emissions trading market.

We thus hope that this discussion will help to clarify the issues, and we invite Keenlyside et al. to a guest post here (and at KlimaLounge) to give their view of the matter.


198 Responses to “The Global Cooling Bet – Part 2”

  1. 101
    Jari Worsley says:

    First post on Realclimate from me. Very good site. Thank you for helping me form opinions on the science (I’m a lapsed Geologist/Biologist so i can follow a lot of it, but have not kept up to date since the early 90′s)

    you are right to be concerned about media coverage of this. The New Scientist in the UK is reporting this in a misleading way:

    “The controversy is unlikely to go away. A study in Nature this month (vol 453, p 84) led by Noel Keenlyside of the Leibniz Institute of Marine Sciences in Kiel, Germany, forecasts that this cyclical warming would soon abate. “There could be some cooling in Europe and North America over the coming decade as the natural cooling offsets the warming from human activities,” Keenlyside says.”

    – that’s at the end of an article on the Rosenzweig et al study published recently in Nature on the impact of climate change on plants and animals. Presumably New Scientist have put this in as a counterpoint. It is very misleading though. No “this is only an experiment” or “not everyone agrees with this result” etc.

    and i always thought New Scientist was a good magazine. just goes to show how messages can get distorted very easily.

    http://environment.newscientist.com/channel/earth/mg19826564.400-life-feels-the-effects-of-a-changing-climate.html

  2. 102
    Alan Millar says:

    I like to think for myself and hypothesize what would the Earths climate be like if Mankind did not exist.

    Assuming that was so. :-

    We are in a warmer interglacial period would I therefore expect the climate to be warming, to be stable, or to be cooling?

    Would I expect Glaciers and ice coverage to be reducing, to be stable, or to be increasing?

    The information I would really need to know, I think, is whether, the non mankind influenced, inter glacial period had reached its maximum or not and was now in decline.

    Does anyone know for certain?

    Therefore, when you put mankind back into the equation how can anyone postulate that mankind is having any influence either way?

  3. 103
    Hank Roberts says:

    Alan, if you want “for certain” you need either the mathematics department or a religion — they’re the ones who can prove statements beyond any doubt, as long as you accept their basic assumptions.

    Science doesn’t offer that kind of certainty.

    Do you ever gamble? Fly on an airplane? Use a device with a semiconductor in it, like a laser, CD player, phone, or computer?

    Those are all matters of probability, not certainty.

    If you’ll accept the level of likelihood we use day to day in using science and what’s developed from it, you can have a very good likelihood of an accurate answer.

    Interested? Read more. Try the “Start Here” link at the top of the page. Put any term or name you read about elsewhere into the Search box.

    Oh, and consider just looking at the pictures.
    Here’s one:
    http://svs.gsfc.nasa.gov/stories/greenhouse_20020103/images/figure1m.gif

    Remember chlorofluorocarbons? hair spray? refrigerants? the ozone hole? Those also are greenhouse gases.

    So, yes, it IS possible to do what you ask, figure out what difference human contribution makes.

    And, yes, it IS possible to do something about it. We already have.

  4. 104
    Alan Millar says:

    Hi Hank

    So what would your guesses be for the Earths current climate if Mankind didn’t exist?

  5. 105
    wmanny says:

    103. Careful. Paradigm shifting. Dichlorine peroxide break-down rates not as previously understood. Science consensus being called into question, as invariably happens throughout the history of science. TBD whether Montreal has proven to have changed much.

    [Response: The recently reported revisions to the rate constants are inconsistent with clearly observed shorter time variability. Many people more directly involved in ozone chemistry than I do not expect them to stand up. - gavin]

  6. 106
    Rod B says:

    Hank, the relative/historical forcings set me back abit. A question out of right field: what happened to the 30-50years it takes (took?) for a CFC moleculae to make it to the stratosphere?

  7. 107
    Hank Roberts says:

    Rod, if you would check your own beliefs before posting them as assumed truths, it would save me a lot of unnecessary typing. I’m trying to teach you how to be a good skeptic, you know. Trust me on this. You -can- get there. I’ve got to go spend time helping inlaws with a sick kid for a few weeks starting soon.

    You’re ready to solo. Go for it. Last time, let’s do the exercise:

    Standard question — what’s your source? Why do you believe the number? Where did you get it?

    I did a Google search for “30-50 year” and — lo, are we surprised? — find that in posts from the people still claiming “the ozone hole is a fiction” on blogs.

    Nothing in any science sites I found — got any other source for the notion you have?

    Let’s try Google Scholar:

    http://www.sciencemag.org/cgi/content/abstract/272/5266/1318
    That suggests five to seven years would be about right, though it’s an early and optimistic post, things didn’t work out that well.

    A little more searching (you can figure out the terms, the minus sign rules out terms you don’t want, like “ocean” in searching).

    “… stable and reach the stratosphere unchanged over a five to seven year period following release into the atmosphere. CFC and HCFC. molecules are then …”
    http://www.uneptie.org/outreach/wssd/docs/sectors/final/refrigeration.pdf

    OK? Three minutes. You _can_ do this.

    Now, the thinking part. Dang “wisdom” button still not programmed.

    What was that graphing? Global warming potential. How big is the GHG potential of chlorofluorocarbons?

    You can look it up. I trust you.

    Thinking it through, where do greenhouse gases operate? “Whevever they want to sit.” As they say about the 800 pound gorilla. The time lag getting to the stratosphere has no relation to the greenhouse warming potential of the chlorofluorocarbons.

    Yes, they persist, they do over time (not that long either) reach the stratosphere where they also catalyze ozone breakdown, that changes ozone levels, and that has a greenhouse forcing effect — but that’s a different aspect of their chemistry/physics than greenhouse gas-ing.

  8. 108
    Hank Roberts says:

    Alan, if mankind didn’t exist — or if we’d invented something better than burning coal and hadn’t started the current experiment? Well, look at the past.
    This may help, look at the cited papers and the citing (subsequent) papers with the links in the sidebar:
    http://www.sciencemag.org/cgi/content/abstract/240/4850/293

    This may help; the black line goes vertical at the right margin, note the arrow labeled “2004″ pointing to where it was at that time. The last 200 years are in the tiny little bit of the chart right of the tickmark.
    http://www.globalwarmingart.com/images/b/bb/Holocene_Temperature_Variations_Rev.png

  9. 109
    Cheska says:

    What kind of function line (equations) are they using that is rendering their probability outcomes within their programming that is being used in their varying computer models
    and what did they base that, or those, functions and or equations on?

    All computers,computer modeling included, are subject and constrained to the limits of programmer and program itself. The math go to string inputs contained within the programming.

  10. 110
    Toby says:

    Hi

    I’m new here. Have only been folowing the AGW debate for a little while so please excuse me if my question has been answered already. I’m definitely on the fence. It sure is fasinating!

    My question: Does RC believe that increases in C02 leads or follows increased temps?

    Thanks.

    [Response: The carbon cycle is both affected by climate and, through the greenhouse effect, affects climate. Therefore the answer is both. If climate changes through some other factor (say Milankovitch forcing), the carbon cycle will follow and amplify the change. If you add carbon to the system (i.e right now or at the Paleocene-Eocene Thermal Maximum), climate will follow. You might as well ask whether chickens or eggs lead or follow. - gavin]

  11. 111
    Jim Cross says:

    re 97

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

    The five year average at the end of the 1930′s and the five year average in the mid 1990′s is only around .2 degrees different but CO2 is up over 20% between those times.

    I’m not saying it was as warm as it is now in the 1930′s and I’m not denying that the difference right now is closer to .4 degrees from the 1930′s. I am just asking for an explanation of why raising CO2 over 20% didn’t create more warming than it did.

  12. 112
    Geoff Wexler says:

    re #93

    Google and climate change. You have done a good job replying to #90. Just one comment. You have advised John to use Google and your examples may have been good ones for doing that. The trouble is that he may have started with Google as his main source anyway. He might come back at you with ‘Google solar changes’ or some such. Using Google with discrimination is a skill which needs to be learned and is perhaps hard to teach. I am beginning to despair about Google when it comes to this subject. When Channel 4′s Great Global Warming Swindle came out in the UK I was surprised to receive enquiries from graduates who decided to check up on the programme by using Google and immediately found it to be confirmed. This is of course one of the arguments for the existence of Realclimate but some people (especially those who don’t like authority) end up by being completely confused.

    Whereas the world wide web used to be mainly a means of sharing science and other academic material it has become joined at the hip with the media in general and is now open to purchase by those with money to spend. Since Google Scholar may be too technical it might be possible to use more specific suggestions like giving the whole link,Googling for the subject + Wikipedia,or + the Met Office etc. or Googling for a named person or group. If this sounds like censorship I would argue that I am not arguing for anything as absurd as a ban, just a bit of guidance. No one would recommend say the UK’s Telegraphs (Daily and Sunday) as sources for information about climate even though the Telegraphs do report on the subject in between articles by Christopher Monckton. No criticism of #93 intended.

  13. 113

    John Millett writes:

    plus water vapour and sensible heat – I wonder whether the models include these?

    Of course they do.

    The IPCC argues that these effects completely swamp solar ones, on two main grounds: first, the rate of warming in the latter half of the 20th century exceeds all previous experience; and second, otherwise their models don’t make sense.

    The second “argument” is something you made up. The IPCC doesn’t say anything of the sort. Have you actually read the AR4 report? Why don’t you do that before telling us what it says?

    unpublicised revisions to the US temperature record reveal that six of the hottest ten years occurred in the first half of the 20th century.

    What “unpublicized revisions?” Are you making stuff up again? And what makes you think US continental temperature records, or central England temperature records, reflect what’s true for the whole world? Do you understand what an ‘average’ is?

    I would also like a climate scientist to confirm that, in and of itself, CO2 would block no more than 0.04% of out-going infra-red radiation.

    No climate scientist in his right mind is going to “confirm” something that just isn’t true. CO2 accounts for 26% of the clear-sky greenhouse effect according to Kiehl and Trenberth (1997):

    http://www.atmo.arizona.edu/students/courselinks/spring04/atmo451b/pdf/RadiationBudget.pdf

  14. 114

    Jim Cross posts:

    I’m not saying it was as warm as it is now in the 1930’s and I’m not denying that the difference right now is closer to .4 degrees from the 1930’s. I am just asking for an explanation of why raising CO2 over 20% didn’t create more warming than it did.

    Well, let’s find out. The radiative forcing approximation for carbon dioxide under near-present conditions is:

    RF = 5.35 ln (C/C0)

    where C is present or end concentration and C0 is reference concentration. (C/C0) according to you is 1.2 for the period in question. 5.35 ln 1.2 = approximately 0.98. Using a climate sensitivity of 0.75 K/W/m2, that translates to 0.73 K. The actual rise was 0.4 K.

    I suggest that the discrepancy is probably due to the massive release of anthropogenic aerosols which caused the cooling in the ’40s and has created a negative temperature feedback since. You would only need a cooling of 0.33 K over 70 years to match.

  15. 115
    John Millett says:

    #92Thank you, Phil Fenton. I have difficulty with the notion that any matter making up a proportion “x” of a medium can intercept a proportion “250x” of waves passing through the medium. All waves would pass through an atmosphere comprising only N2 or O2. No waves would pass through an atmosphere comprising only CO2. But, you imply, less than half the waves (much less, perhaps zero)would pass through an atmosphere of half CO2 and half N2 or O2. Why is this so? On the other part of your answer to my query, I take it that heat would be transferred from CO2 molecules to N2 and O2 by conduction? And that this would raise the intensity of radiation from the atmosphere to the surface?

  16. 116
    Phil. Felton says:

    Re #115

    “#92Thank you, Phil Fenton.”
    That’s Felton.

    “I have difficulty with the notion that any matter making up a proportion “x” of a medium can intercept a proportion “250x” of waves passing through the medium.”

    Perhaps you should read up on light absorption and spectroscopy then! Ever heard of an emerald?
    It’s a gem composed of the transparent mineral beryl, it looks green because all the blue and red light is absorbed by an impurity, chromium, which is present at less than 1%.

    “All waves would pass through an atmosphere comprising only N2 or O2. No waves would pass through an atmosphere comprising only CO2. But, you imply, less than half the waves (much less, perhaps zero)would pass through an atmosphere of half CO2 and half N2 or O2. Why is this so?”

    No because only those wavelengths between ~13 and 17 microns will be absorbed by CO2, in that band almost all will be absorbed within a few meters.
    http://webbook.nist.gov/cgi/cbook.cgi?Spec=C124389&Index=1&Type=IR&Large=on

    “On the other part of your answer to my query, I take it that heat would be transferred from CO2 molecules to N2 and O2 by conduction?”

    By collisions.

  17. 117
    Ray Ladbury says:

    John Millett, I find it more illuminating to think of it this way. Imaging a photon of wavelength roughly 15 microns propagating upward through the atmosphere. If it encounters a CO2 molecule during its ascent, it is likely to interact with it and excite the vibrational state, right? So what is the probability that it will encounter a CO2 molecule?
    CO2 constitutes 385 ppmv, which is about 600 ppm by mass. A COLUMN OF AIR 15 MICRONS IN RADIUS weighs roughly 7.2 mg. That means there are roughly 59 trillion CO2 molecules encountered by every 15 micron photon on a straight-line path out of the atmosphere. The photon is, effectively, a sitting duck. Moreover, the lifetime for radiative decay of the corresponding excited vibrational state is of order microseconds, so the state is much more likely to decay collisionally than radiatively. It thus imparts energy to N2 and O2, Ar–the whole atmosphere.
    Thus, the chances of an IR photon in the CO2 energy band are pretty slim until the radiation occurs high in the atmosphere.
    As to radiation transfer–within the atmosphere there are many ways energy can be transferred to the surface. It’s not just radiation.

  18. 118
    Geoff Wexler says:

    Re #116

    (In case Phil Fenton misses #116 )
    “I have difficulty with the notion that any matter making up a proportion x of a medium can intercept a proportion 250x of waves passing through”

    Experiment: Try a mixture of one part of potassium permanganate and 250 parts of water.

    Theory. Since the oxygen and nitrogen are transparent to infra-red they might as well be ignored, at least for the first absorption. That would still leave a large number of closely spaced CO2 and H2O molecules.

    “On the other part of your answer to my query, I take it that heat would be transferred from CO2 molecules to N2 and O2 by conduction? And that this would raise the intensity of radiation from the atmosphere to the surface?”

    If you are thinking of radiation from oxygen or nitrogen that would be negligible because a zero absorber is also a zero radiator.This is an application of laws discovered by Kirchoff, Angstrom (the older one) and I believe Rayleigh.

  19. 119
    Jim Eager says:

    Re Geoff Wexler @ 112:
    Geoff, I would strongly agree with your comments about being careful when using google, but since I was suggesting that John Millett use it to look up something as uncontroversial as relative humidity I wasn’t too worried. But you are right when it comes to more controversial subjects such as the PETM, the end Permian, snowball Earth, and even the Milnkovic cycles. In fact I recently had someone try to refute Milankovic forcing by citing strenuous arguments made by a proponent of ‘intelligent’ design. :)

  20. 120
    Rod B says:

    Hank, Carl Sagen, of global warming and global winter fame (among other stuff) said 50 years. I recall reading also a number of years back as much as 100 years for CFCs to make it to the stratosphere. I assume the science and our understanding have improved since then, as opposed to, say, burying it as “downright embarrassing: ;-). It still seems a little tough for the very heavy CFC molecules to get to the top of the troposphere and then through the narrow gate of the tropopause in a half-dozen years. But, as you say, it’s just a thought; I have no studied reason to dispute it.

    Actually the answer to my ill-posed (as it turns out) question was the transit time to the stratosphere has little to do with CFC greenhouse gas potential. Though that potential blew me away (new news for me).

    Good luck with your helpful sojourn.

    [Response: Look up "age of air". For the polar stratosphere you get mean numbers like 4 or 5 years (though the tail of age distribution can be quite long). You can deduce this from estimates of SF6 concentrations, Radon measurements (both ground sources with 'clocks' attached), or from the decay of bomb 14C for instance. Rind et al 1999 has a good discussion. - gavin]

  21. 121
    Rod B says:

    Ray (117) good analysis that I will explore thoroughly with your start. But you left me hanging with, “…As to radiation transfer–within the atmosphere there are many ways energy can be transferred to the surface. It’s not just radiation.” Which might be true, but my long-standing question is what is the source of the massive IR radiation from atmosphere to surface?

  22. 122

    # 120 Usually when a scientist asks for a reference they don’t mean an unsubstantiated claim that some famous person said it. They mean a published result in the literature. Having such a source (like the one Gavin provided) doesn’t in and of itself mean that the number is correct. What that really does is provide a hook into the literature that one can use to ascertain whether a particular result is in the right ballpark by looking to see if the result in question is pretty well accepted in the literature or if there is substantial dispute within the literature. The time for CFC’s to reach the upper atmosphere seems like a relatively straightforward thing to measure. It is unlikely that it is in dispute. I expect that in all probability you are misquoting Sagen and incorrectly remember your reading from “a number of years back”.

  23. 123
    David B. Benson says:

    Alan Millar (102) — The peak of the Holocene interglacial is long past. Without humans the climate would be slowly cooling towards the next attempt at a stade (massive ice sheets) in about 20,000 years.

  24. 124
    Hank Roberts says:

    Rod, I know you hear this over and over, but:

    It will _really_help_ you to read Spencer Weart’s book, first link under Science, right hand side of the RC page.

    You’ll ask better questions, knowing the basics. The effect of the CFCs is among those discussed there.
    http://www.aip.org/history/climate/othergas.htm

  25. 125
    Maya Chase says:

    The wiki link in post #14 didn’t work exactly right for me, although it seems to be the same as the page on which I eventually landed:

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

    However, if you go there and it still doesn’t work, use the search that they suggest and you will quickly come to the right page. I will keep this link in mind for skeptics who try to tell me that there’s no global warming because “even scientists don’t agree.”

    I just want to thank everyone who works to keep RC up and running – it’s a wonderful resource!

  26. 126
    Ray Ladbury says:

    Rod, I didn’t mean to imply that there is no radiation from the atmosphere to the surface, merely that that is not the only energy transport mechanism. CO2 or H2O molecules near the surface can and will radiate at their blackbody temperature–again equilibrium. However there are other transport mechanisms for energy to make it back to the surface.

  27. 127
    John Millett says:

    #93 Thank you, Jim Eager. Apart from the abnormal climate change events you mention, the numerous oscillations between ice ages and inter-glacial warming periods also express natural causes (most likely related to solar impacts of one kind or another – if not, what else?) making the case for AGW dependant solely on the unprecedentd rate of current warming. Suitably chastened, I looked at the revised US data you helpfully posted and found they make an interesting pattern. The hottest 25 years in the record occurred over 107 years from 1990 to 2007 and show a slight warming trend. Trimmed of the three observation greater than an anomaly of 1.00 and the two less than 0.6, the remaining 20 span the 76 years from 1931 and show an even slighter warming trend. That there is a warming trend in an inter-glacial period is unsurprising: that it is so slight, given the AGW hypothesis and the rapid increase in CO2 emissions over the period, is surprising.

  28. 128
    Hank Roberts says:

    John, the USA has been on the low side — that fits what the climate models suggest will happen, given the ocean and atmospheric circulation.

    http://hadobs.metoffice.com/hadcrut3/diagnostics/monthly/anomaly.png

    Look at the global data. This is helpful:

    http://bp3.blogger.com/_7NrAt8xGd0E/SCXfzDRcsJI/AAAAAAAAAts/JNe5Nuf0A9o/s1600-h/20080429.gif

    News article about it here:
    http://www.sciencedaily.com/releases/2006/12/061218130705.htm

  29. 129

    Re: 100

    Then you say: “I would also like a climate scientist to confirm that, in and of itself, CO2 would block no more than 0.04% of out-going infra-red radiation.”

    Where the heck does that come from? Are we talking IR energy or IR photons?

    I believe it was misquoted by a factor of 10 from an old study of Arrhenius that I learned of in the beautiful work of Spencer Weart that I learned of from Hank Roberts in #124:

    http://www.aip.org/history/climate/co2.htm#N_7_

    “These measurements and arguments had fatal flaws. Herr Koch had reported to Ångström that the absorption had not been reduced by more than 0.4% when he lowered the pressure, but a modern calculation shows that the absorption would have decreased about 1% — like many a researcher, the assistant was over confident about his degree of precision.(8a) But even if he had seen the1% shift, Ångström would have thought this an insignificant perturbation. He failed to understand that the logic of the experiment was altogether false.”

  30. 130
    Ken Feldman says:

    Barton Paul Leveson writes (114)

    Well, let’s find out. The radiative forcing approximation for carbon dioxide under near-present conditions is:

    RF = 5.35 ln (C/C0)

    where C is present or end concentration and C0 is reference concentration. (C/C0) according to you is 1.2 for the period in question. 5.35 ln 1.2 = approximately 0.98. Using a climate sensitivity of 0.75 K/W/m2, that translates to 0.73 K. The actual rise was 0.4 K.

    I suggest that the discrepancy is probably due to the massive release of anthropogenic aerosols which caused the cooling in the ’40s and has created a negative temperature feedback since. You would only need a cooling of 0.33 K over 70 years to match.

    If I understand the science behind climate sensitivity correctly, with a climate sensitivity of 0.75 K/W/meter squared there’s approximately 0.4 to 0.6 K of warming in the pipeline. That extra warming would become apparent if the climate were allowed to reach equilibrium without further forcing.

    So the observed rise of 0.4 degrees coupled with the warming in the pipeline (of at least 0.4 degrees) would be more than enough to equal the amount due to greenhouse gas forcing, even with some of the temperature rise masked by aerosols, wouldn’t it?

    Ken

  31. 131
    Nigel Williams says:

    Sorry if its slightly OT, but tab between say http://manati.orbit.nesdis.noaa.gov/ice_image21/D08136.NHEAVEH.GIF
    And
    http://manati.orbit.nesdis.noaa.gov/ice_image21/D08139.NHEAVEH.GIF
    and have a look at the way the remaining multi-year sea ice of the Arctic is peeling away from the Canadian Archipelago. Bets? A sure thing, more likely!

  32. 132
    John Millett says:

    #100 Thank you, Ray Ladbury. I’ve got the message on the abnormal climate change events from Jim Eager, as well (#93 and my response #107 (awaiting moderation)). “Are we talking IR radiation or IR photons?” Ray, I thought they were much the same thing; but if not, I don’t think I want to go there – it’s bound to be too complicated. “How do you give a single molecule a temperature?” Courtesy of #92, by placing it in the path of a particular wave length of IR radiation. Chastened again, I’ve gone to “CO2 in 6 easy steps” where step 1 made me wonder, unmasking a simple (and ancient) engineering background, whether a water reservoir was analagous to the atmoshere? Pumping water into a reservoir at a faster rate than it is draining out results in the reservoir overflowing. What happens to all those watts accumulating in the atmosphere as the surface pumps in energy at 1.6 times the rate at which it escapes to space?

    #117 Ray, what you didn’t tell me is that as well as the 59 trillion photon-gobbling CO2 molecules in the air column there are 98 quadrillion photon-friendly molecules of N2 and O2. The probability of the photon escaping to space is 0.9994, no?

  33. 133

    #114 Barton Paul Levenson:

    … that translates to 0.73 K. The actual rise was 0.4 K.

    Mostly correct, I think. Note that 0.73K represents equilibrium warming; what we want is transient warming, only about half of that, the rest going into long term ocean warming. I don’t think we need aerosols here to make the books close (and the large aerosol cooling effects are mostly for the period 1940-1975 anyway).

  34. 134

    Ken and Martin — good point. I had forgotten that the RF in the Myhre et al. equation was for equilibrium warming, and that some warming is still coming.

  35. 135
    paulm says:

    Is it possible for the ice cap/sheets to melt (completely) in the north and build in the south?

    What effect could this have on earths orbit/rotation/climate?

  36. 136
    tamino says:

    Re: #135 (paulm)

    Yes, it’s possible. Right now the far north is warming faster than any other region of the planet, but the far south only very slowly.

    I doubt there’d be any effect on our orbit, but I recall (don’t recall where) seeing statements that the re-distribution of mass due to ice melt can affect earth’s rotation. If I recall correctly, it’s expected that mass will be transferred equatorward, which will slow earth’s rotation but only by a tiny amount. Again, I doubt that the miniscule change in rotation rate will have a noticeable climate effect. This is all speculation on my part.

  37. 137
    Rod B says:

    John (132), a quicky minor clarification. A photon absorbed into vibration energy of CO2 does not raise its temperature. Though this is mostly academic as it turns into higher temperature when it collides with another air molecule. Two, I don’t think you can call N2 or O2 photon friendly.

  38. 138
    Jim Eager says:

    Re John Millett @127: “the numerous oscillations between ice ages and inter-glacial warming periods also express natural causes (most likely related to solar impacts of one kind or another – if not, what else?)”

    Natural, yes, and initiated by changes in solar insolation, yes, but not as a result of variations in solar output, rather as a result of changes in Earth’s orbit, tilt and wobble of axis. See Milankovic Cycles from my post 93. But CO2 (and methane) emitted by thawing permafrost and tundra bogs, and CO2 emitted by a slowly warming ocean then amplifies the insolation induced warming.

    John: “making the case for AGW dependant solely on the unprecedentd rate of current warming.”

    Not at all. The case for AGW rests on multiple lines of evidence, but most fundamentally on the known radiative physics of CO2 and other greenhouse gases. If CO2 from a warming ocean naturally causes more warming, then CO2 added directly to the atmosphere from fossil fuels will cause more warming. Add to that the fact that fossil fuels have a low ratio of carbon 13 to carbon 12, and that the ratio of 13C to 12C in atmospheric CO2 is dropping as CO2 concentration is rising, means that the increase must be from burning fossil fuels.

    John: “Trimmed of the three observation greater than an anomaly of 1.00 and the two less than 0.6, the remaining 20 span the 76 years from 1931 and show an even slighter warming trend.

    Sorry, dropping any of them is not an option. But even if you do, those 20 may span 76 years, but 12 of them are still from the last 27 years (since 1981). See Hank’s linked graph of ranked global anomalies here: http://www.metoffice.gov.uk/corporate/pressoffice/2008/pr20080429.html

    John: “That there is a warming trend in an inter-glacial period is unsurprising: that it is so slight, given the AGW hypothesis and the rapid increase in CO2 emissions over the period, is surprising.”

    Why? First, the increase in temp from increasing CO2 is not linear, it is logarithmic. Second, a very large and massive heat sink covers 70% of Earth’s surface, meaning much of the added heat is not in the atmosphere. Third, look up ‘global dimming’ caused by aerosols, and ‘Asian brown cloud.’

    And @132 John asked Ray: “whether a water reservoir was analagous to the atmoshere? Pumping water into a reservoir at a faster rate than it is draining out results in the reservoir overflowing.”

    Not necessarily overflowing, but definitely rising. Yes, a reservoir (or bucket, or bathtub) with different outlet levels is a useful analogy. When the water level (temperature) reaches a new outlet or hole the outflow will once again equal the input, but the level (temperature) will be higher.

    John: “What happens to all those watts accumulating in the atmosphere as the surface pumps in energy at 1.6 times the rate at which it escapes to space”

    The elevation at which IR photons are more likely to escape to space than to be absorbed rises, the atmosphere warms, the warmer atmosphere and back radiation warms the surface and ocean.

    John: “Ray, what you didn’t tell me is that as well as the 59 trillion photon-gobbling CO2 molecules in the air column there are 98 quadrillion photon-friendly molecules of N2 and O2.

    The N2 and O2 molecules are transparent to the photons, but they are energised through collision with the excited CO2 (and H2O) molecules.

  39. 139
    Toby says:

    Thank you for taking the time to answer my question. I’m starting to see just how complex this issue really is.

  40. 140
    Ray Ladbury says:

    John Millett, Not to bring back unpleasant memories ;-), but remember back to you modern physics class–an atom or molecule can only absorb radiation with an energy equivalent to the difference between two states of the atom/molecule. O2 and N2 being diatomic, do not have any rotational states or vibrational states that will absorb in the IR. Far from being IR “friendly,” they don’t even wave as the photon goes whizzing past. Ah, but you will ask, what about water vapor? A wonderful greenhouse gas, but 1)water vapor content of the atmosphere has not changed significantly (CO2 has increased by 38%) and 2) water vapor peters out at the cloudtops, while CO2 is well mixed (and continues to work as a ghg and absorb IR) up into the stratosphere.
    My point about whether you were talking about photon numbers or energy is not that complicated–the energy is just the integral of photons at a given energy times the energy integrated over the range of interest–that is, the first moment wrt energy.
    And your instincts are pretty good–the mathematics are similar to the “hole in my bucket, dear Liza, dear Liza” problem. As long as energy in=energy out, you have equilibrium (by definition). Now if you stop some of that energy leaving (and the only way it leaves is as blackbody radiation peaking in the IR range), things have to warm up, and they will continue to warm up until the energy of the outgoing radiation (mainly that outside the absorption bands of the greenhouse gasses) is equal to the incoming radiation. Does that make sense?

  41. 141
    Hank Roberts says:

    John, look through a pane of glass — it’s almost clear in the visible light range. Look through it edgewise and it’s very green. The CO2 and other greenhouse gases in the atmosphere are trace gases, but between the ground and outer space, any photon will have a very high likelihood of interacting rather than escaping the planet. Only the greenhouse gases near the top of the atmosphere are emitting infrared photons that, if they go up, are likely to escape the planet. (At those elevations you have CO2, chlorofluorocarbons and such; the water is mostly frozen out much lower down.)

  42. 142
    Geoff Wexler says:

    Re #140 Ray Ladbury.

    Haven’t you gone a bit too far in downgrading the importance of water vapour?

    You wrote:
    “1)water vapor content of the atmosphere has not changed significantly (CO2 has increased by 38%) and 2) water vapor peters out at the cloudtops, while CO2 is well mixed (and continues to work as a ghg and absorb IR) up into the stratosphere’

    A casual reader might conclude from these remarks that positive feedback from water vapour is of no importance. Since the water vapour ought to go up at a rate of 6% per degree C there must already been an increase in H2O thus contradicting your point 1). I thought that this had also been confirmed by observation. Furthermore at high altitudes the spectra of water vapour and CO2 act as distinct lines which implies that the radiation from the highest H20 molecules ought to reach the top of the atmosphere without further absorption by CO2. Isn’t that right?

  43. 143
    Hank Roberts says:

    > water vapour … up at a rate of 6% per degree C

    But the stratosphere is cooling, not warming.

    > at high altitudes … which implies

    What altitude is “high”? What’s your cite on this?

  44. 144
    Ray Ladbury says:

    Geoff, Thanks for correcting any misimpression I might have left. Yes, as temperature rises, water vapor content does act as a feedback. My point was that water vapor could not be the driver. I believe that even high in the atmosphere, there is overlap between CO2 (15 micron band) and water vapor spectra. It does look like it from the spectra I’ve seen, but I’m sure Gavin or somebody else will correct me if I am wrong.

  45. 145
    Geoff Wexler says:

    Re #137

    ” A photon absorbed into vibration energy of CO2 does not raise its temperature.”

    Sounds like a dubious remark to me. If you plug the original temperature into the standard equilibrium formula it would tell you that the molecule is probably not vibrating i.e. you have made an error. The definition of temperature here is mainly a matter of terminology. From some standpoints it might be convenient to define a raised effective temperature.

    The main point is to keep tabs on where the energy is gone and how it is shared out between the different degrees of freedom.

  46. 146
    Hank Roberts says:

    Geoff, this may clarify the overlap:

    http://earthobservatory.nasa.gov/Study/Iris/Images/greenhouse_gas_absorb_rt.gif
    “… what makes carbon dioxide so interesting is that the gas absorbs energy in some small segments of the thermal infrared spectrum that water vapor misses. …”

  47. 147

    reiterating 146′s remark: Weart http://www.aip.org/history/climate/co2.htm writes:

    Improved physics theory and precise laboratory measurements in the 1940s and after encouraged a new way of looking at the absorption. Scientists were especially struck to find that at low pressure and temperature, each band resolved into a cluster of sharply defined lines, like a picket fence, with gaps between the lines where radiation would get through.(24) The most important CO2 absorption lines did not lie exactly on top of water vapor lines. Instead of two overlapping bands, there were two sets of narrow lines with spaces for radiation to slip through. So even if water vapor in the lower layers of the atmosphere did entirely block any radiation that could have been absorbed by CO2, that would not keep the gas from making a difference in the rarified and frigid upper layers.

  48. 148
    lorax73 says:

    my uncle sent me this.
    is this global cooled 0.7C in 2007 ..is this number real or relevant or meaningful?
    – lorax73
    =====================================

    —-Original Message—–
    From: Jack Perrine
    Sent: Sun, 18 May 2008 7:09 pm
    Subject: SORRY TO RUIN THE FUN, BUT AN ICE AGE COMETH

    [ I find this particularly amusing. In the late 70's I had a friend
    who was an editor at the National Climate Center in Boulder Coloado.
    He pointed me at a few books on the coming glacial age. Then all of
    a sudden he was pointing me at books on Global warming. What was so
    amusing at the time was they both seemed to be the same books if one
    looked carefully: a large part of the text was the same while the indexes
    and title pages had been changed. But now below you can see a very good
    article on a coming ice that could come close to destroying civilization
    ......and yet our stupid politicians are still working on bankrupting
    the world with their funny CO2 and Global Warming

    Jack ]

    OPINION: SORRY TO RUIN THE FUN, BUT AN ICE AGE COMETH

    The Australian, 23 April 2008
    http://www.theaustralian.news.com.au/story/0,25197,23583376-7583,00.html

    Phil Chapman

    [edit]

    [Response: No. In the same way that a drop of 10 deg C from one day to another can't be extrapolated to a cooling of 100 deg C in ten days, month-by-month temperature changes (associated in this case mainly with La Nina in the Pacific) can't be extrapolated to decades. This was neither unusual nor exceptional, and will disappear as the La Nina does. I suggest keeping the email and showing it to your uncle in a year's time and asking him about his predictive skill. - gavin]

  49. 149
    Phil. Felton says:

    Re #144

    Try http://www.spectralcalc.com/spectralcalc.php
    Run it for CO2 & H2O between 600-700 cm^-1 at a pressure of 10mbar.

    Not too much overlap.

  50. 150

    For those who want global warming to increase temperatures every year, do you think the average temperature every year would be constant without an external impulse?

    If not, you have to consider how a long-term warming trend would look if you superimposed it on short-term variations.

    My approach to this was to look for a period in the temperature record where there was no discernible long-term trend, the first 50 years of HadCRUT3 (1850-1899). If you look at this data, you will see that the variation between the maximum and minimum annual average is over 0.5°C with variations of over 0.4°C in as little as 2 years. A linear regression shows a trend of warming of 0.08°C per century with r2 = 0.0124.

    What would have happened if you had superimposed today’s level of CO2 forcing onto that situation? You would have had a long-term trend of increasing temperature and the odd patch where the trend was flat or even down. See http://opinion-nation.blogspot.com/2008/04/why-doesnt-it-get-hotter-every-year.html for more detail (comments and corrections welcome as always).

    Given that I artificially forced this trend onto data which didn’t have a significant warming trend before, this is some indication of why you shouldn’t expect to see a monotonic increase in temperatures under today’s conditions. The only way I would expect that to happen would be if the warming signal was above inter-annual natural variability. Given that we are talking about a trend which is accelerating to around 3°C per century, or only 0.03°C per year, it’s not surprising that every year is not warmer than the last.


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