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Climate Hustle

Estimating climate sensitivity from 3 million years ago

Posted on 9 May 2010 by John Cook

A key question in climate science is climate sensitivity. If the amount of CO2 in the atmosphere is doubled, the change in global temperature without feedbacks would be around 1°C. However, a number of feedbacks do occur - water vapour, snow albedo, sea-ice albedo and clouds. These respond relatively quickly, over a time-frame of years to decades, and are called "fast feedbacks". Modelling all the individual feedbacks can be problematic. However, we can empirically sidestep all this by using paleoclimate data to calculate the net response from fast feedbacks. A number of studies looking at various periods of Earth's past converge on a climate sensitivity of around 3°C (Knutti & Hegerl 2008). This means any initial warming is further amplified by positive feedback.

A new paper Earth system sensitivity inferred from Pliocene modelling and data (Lunt 2010) looks further into climate sensitivity as determined from the past. It examines the mid-Pliocene warm period,about 3.3 to 3 million years ago. This period is useful because CO2 levels and temperature were higher than pre-industrial conditions, giving us an insight into how climate responds when it's already warm. At this time, the main external forcing driving climate was tectonic changes in mountain ranges which led to changes in atmospheric CO2 (driven by both tectonic-related emissions and weathering).

What they find is the temperature response to changes in CO2 is 30 to 50% greater than the response based on fast feedbacks. This is due to other feedbacks operating over greater timescales (there is still uncertainty over the timescales involved, from hundreds to thousands of years). These slow feedbacks include changes in dust and other aerosols, vegetation, ice sheets and ocean circulation. This is confirmed by the geological record which records changes to ice sheets and vegetation over this period.

This means climate may be more sensitive to carbon dioxide than previously thought. On top of the fast feedbacks that cause the climate sensitivity of 3°C, additional slow feedbacks will add another 1 to 1.5°C warming. This result is confirmed by another recent paper also studying the Pliocene (Pagani 2010). This higher sensitivity should be taken into account when targets are set for limiting greenhouse gas emissions.

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Comments 51 to 100 out of 115:

  1. HumanityRules at 17:48 PM on 11 May, 2010
    "Your list doesn't seem to include any of the so-called sceptics papers?"

    Actually I've just had a look at Ari Jokimäki's list. Of course it depends on what you mean by "so-called sceptics papers", but if you mean papers by individuals that arrive at low climate sensitivity by hopelessly flawed analysis, or more generally any paper that infers a cimate sensitivity below the likely IPCC range (e.g. below 2 oC of equilibrium surface warming per doubling of atmospheric [CO2]), then the list has lots of "so called skeptics papers".

    e.g. referring to my brief list in post 49 above, Ari has:

    Chylek and Lohmann (2008)

    Schwarz (2007)

    Shaviv and Veizer (2003)

    and there is also:

    Washington and Meehl (1989)
    Mitchell and Ingram (1989)
    Gillard and Schneier (1984)
    (Idso (1980)
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  2. Chris, I agree 100%. The last thing the IPCC (or anyone) should be doing is classifying papers into "skeptic papers" and "pro-AGW papers" and then for the sake of evenhandedness being sure to cite three from column A and three from column B.

    There have been lots of good studies of climate sensitivity. Some find higher values (Lunt 2010, Hansen) while others find lower (James Annan). IPCC should and does consider the range of findings among strong, well-conducted studies in the literature.

    On the other hand, there are also papers about climate sensitivity that have serious flaws (Chylek here and here, or Lindzen & Choi here). I don't think IPCC should overlook those flaws and give them unwarranted consideration for the sake of offering "equal time" to all sides. The only distinctions that should matter are whether a paper is insightful, robust in its methods, justifies its conclusions, and leads to further productive research.
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  3. A somewhat related paper was published not long ago also in Nature Geophysics which also indicates the possibility of very significant longer term amplification of greenhouse-gas induced temperatue rises via poorly understood mechanisms.

    Obviously we are aware of the possibility for what might be considered catastrophic non-linear consequences of warming (rapid collapse of polar ice sheets; massive release of methane from hydrates etc.). Unfortunately it's not straightforward to factor these into the analyses of mitigation and adaptation policies.

    R. E. Zeebe et al. (2009)Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming Nature Geoscience 2, 576 - 580.
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  4. HumanityRules (#48) wrote:
    "Is there any justification for putting one year memory rather than leaving it out?"

    Yes. In an earlier study Lin et al. found that the climate memory is at least 8 years, so putting in a short memory instead of no memory is better. But of course, when you are dealing with the real life you need to use a memory > 8 years.
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  5. "If the amount of CO2 in the atmosphere is doubled, the change in global temperature without feedbacks would be around 1°C."

    For the last 100 years, CO2 has gone roughly from 250 ppm to 380 ppm, a ratio of 1.52:1. If the above is true, global warming should be around 1.52 / 2 = 0.76 C. Since climate models assume the Earth's temperature holds within a strict equilibrium, the effect of every extra exothermic calory released since the beginning of the Industrial Revolution should (to some degree) be having a cumulative effect. How can this not be accounted for, especially by those who maintain that with more CO2, the ability of the Earth to discharge heat has diminished?

    The "non skeptic" replies to this question typically indicate that this waste heat is comparably small, however the value provided is only given for one year as opposed to 100 or 200 years.

    A balance scale analogy may be helpful. If 100 kilos are hung across a balance scale, and then a dash salt is added from a salt shaker on one side, a significant movement is not expected; however, if a dash of salt is added everyday for 200 years, eventually the scale will tip.

    As energy cannot be destroyed, it must be accumulating. I think the phrase, "you cant have it both ways" applies, such that if the Earth's thermal balance is so delicate, one cannot ignore the effects of human waste heat, and that some significant part of heating is not coming from CO2. In either case, it is coming from the use of non renewable energy sources.
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  6. RSVP at 00:19 AM on 12 May, 2010

    Not really RSVP. Your analogy isn't a meaningful one in context.

    Here's an appropriate analogy. You live in one room shack in the woods. Your shack is cold (it's the same as ambient temperature) and therefore you light a fire in the fireplace and arrange that this provides a constant thermal output (the equivalent of human "waste heat"). The temperature of the shack rises a bit and stabilises at a temperature whereby heat from the fire is balanced by loss of heat to the outside.

    Note that although "energy cannot be destroyed", it isn't accumulating in the shack. The temperature doesn't keep on rising! The energy is dissipated to the outside.

    You decide that you find the situation still uncomfortably cold. You therefore put a layer of insulation on the outside walls (the equivalent of enhancing the greenhouse gas concentration in the atmosphere). The dissipation of thermal energy to the outside is less efficient and the temperature inside your shack rises until a new equilibrium temperature is reached. Since you quite like the effect you keep on adding to the insulation. Each time the added insulation provides an additional increment of prevention of heat loss and the temperature continues to rise. etc. etc.

    Note btw that if you were to take your scenario to its logical limit then the accumulation of heat in the Earth system would be unbearable. Why go back only 100 years? If energy was "accumulating" then the preceding millenia of forest fires, heat from volcanic eruptions etc would have turned the planet into fiery hell. Happily, the Earth is in radiative balance with its surrounds (at least it tries to be!), and forcings don't result in the continual accumulation of thermal energy; they result in the movement of the Earth system to a new equilibrium state. The equilibrium state resulting from human "waste heat" is a tiny fraction of a degree above the Earth surface temperature that would exist without it....

    ...incidentally, 100 years ago the atmospheric [CO2] was ~ 300 ppm (not 250 ppm). So you need to recheck your maths...
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  7. #51 Chris

    Thanks for pointing those out. It's not straightforward but I had a look see if any made the cut in the 2007 IPCC report. Couldn't find them.

    Shaviv and Veizer (2003)
    Washington and Meehl (1989)
    Mitchell and Ingram (1989)
    Gillard and Schneier (1984)
    Idso (1980)

    More generally I struggle with a pattern that is forming in which any paper that estimates low sensitivity has huge flaws in it while those with estimates around the IPCC range are uncritically accepted. As an example in John's previous list Schwartz is critisised partly on the basis that it uses volcano's which may have different features to other forcings. Yet this is not raised earlier in the list for the Bender 2010 paper (which just happens to have a more acceptable value). It also didn't stop the IPCC from referencing other papers on volcano's or including a whole section on it.
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  8. RSVP #55, setting aside the incorrect atmospheric CO2 figures... your math is also off.

    The statement that a doubling of CO2 without feedbacks causes a 1 C increase in temperatures can be mathematically expressed as;

    X * ln(2Y/Y) = 1 C

    Where X is a constant and Y is the starting CO2 level. Plugging in your values we get ln(380/250)=0.41871. The natural log of 2 (from a doubling, 2Y/Y) is 0.693147. If 0.693147 X = 1 C then 0.41871 X = 0.6 C, not the 0.76 C value you came up with.

    Using the actual CO2 figures for today vs 100 years ago gives ln(387/300)=0.367371 C warming... as opposed to the ~0.7 C actually observed. Ergo, we have observed more warming than can be explained by the enhanced CO2 greenhouse effect. Thus demonstrating that total feedback effects over the past hundred years have been positive. Not to mention consistent with both models and reconstructions of past climate change.
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  9. HumanityRules at 01:53 AM on 12 May, 2010

    HR, Schwartz's paper has got nothing to do with volcanos [*]. So the point you are making is pointless.

    In any case Schwartz himself recognised that his analysis was flawed, and wrote a retraction in which his reanalysis brought his estimated climate sensitivity back into the IPCC range. Are you suggesting that we should continue to include his original analysis in our summary of the science on climate sensitivity even though Schwartz himself says it's incorrect? That would be taking efforts to misrepresent the science to truly heroic proportions!

    As for the 2007 IPCC report. It's rather unlikely that a 2007 IPCC report would include very much of the scientific literature from nearly 20 years previously. This early literature will have been consolidated in reviews, and in any case the role of the IPPC's periodic reports is to bring the state of knowledge of relevant science up to date.

    The Shaviv and Veizer (2003) paper is probably unlikely to have been cited by the IPCC ('though it might have been - why not have a thorough look?). It's really a hypothesis (note the title: "Celestial driver of Phanerozoic climate?" - incidentally the answer is almost certainly no!) and was published in the GSA house journal GSA Today which isn't considered part of the scientific literature (it's not indexed by ISI for example); that's not to say it isn't an excellent magazine btw, nor that the Shaviv Veizer hypothesis wasn't interesting). In any case Veizer subsequently reanalyzed his paleotemperature data, and the hypothesis pretty much fell flat.

    As for your "struggles with patterns forming", it's difficult to konw what to say. Of course if we're interested in the science then we're really interested in the evidence, and perhaps your struggles involve a difficulty getting to grips with that. It would help perhaps if you were to look at the papers you refer to...

    [*] He estimates heat capacity response of the oceans from an analysis of ocean heat uptake, and he estimates a time constant for heat uptake by autocorrelation of the heat capacity during 1880-2004. How can you comment on this paper if you don't know what it's about?
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  10. The "pattern" arises quite naturally, I think. Whenever there's some value being measured, one wishes to explain the outliers. Therefore the studies reporting values outside the regular range are more likely to be checked more thoroughly than the papers giving values within the regular range. It doesn't mean that the papers within range are not checked at all, it just means that papers outside the range are checked more thoroughly to find out why they find such strange values.

    As we have seen here, there are lot of papers that have determined the value of climate sensitivity. In that kind of situation there's not much chance that couple of outliers would be correct (and dozens of others would be wrong), so it's not surprising that we keep finding errors among them.
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  11. HR, let me turn around your implied question: why do you think so many "skeptical" papers about climate sensitivity have turned out to have serious flaws?

    I take it you don't dispute Schwartz's own revisions to his original paper, and I assume you're likewise willing to accept that the problems with Chylek (see here and here) are real. Everybody including Roy Spencer seems to agree that there were significant problems with Lindzen and Choi.

    I would assume that the reason for this "pattern" is presumably that climate sensitivity really is somewhere around 3C, so papers that find much lower values understandably must have flaws or they wouldn't have found such an anomalously low value.

    Do you have a different explanation to suggest?

    Or another question: are there high-quality papers published in the peer-reviewed literature in the past decade that you would point to as convincing and that give a climate sensitivity below 2? I'm not aware of them, but maybe I'm missing something.
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  12. Chris
    Why go back only 100 years?

    100 years or pre-Industrial Revolution is pretty much the baseline condition for the detected changes in CO2 ppm and average global temperature. This is what AGW is focussed on I believe. A "modern" event. What happened before this is irrelevant. Natural cooling may have absorbed/cancelled any significant anthropogenic contributions 20 times in the past for all we know.

    For the point I was making, I assume that the natural fluctuation is completely stable over the last 100 years. The only two things to consider then is effects of greenhouse gases and waste heat. But you cant ignore a cummulative effect of waste heat while at the same time holding everything else constant (and even worse, assuming that the IR lid is even tighter). So some of the warming must be attributed to waste heat.

    The other detail is that you have what is called winter and night. Either global warming is only associated with warmer days and warmer summers, or the heat is accumulating somewhere (and that somewhere is our oceans).
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  13. RSVP,

    I don't think you are understanding Chris's point. As temperatures rise, the rate that heat dissipates into space also rises, until the rate of warming and the rate of dissipation equalize, and the climate is in equilibrium. As long as the rate of warming influences remains constant, there is no accumulation of heat.

    The problem with CO2 is it takes thousands of years for feedback mechanisms to balance out and remove CO2 to a significant extent. As a result, even if our CO2 emissions stabilized at the current annual level, CO2 would still accumulate in the atmosphere. As the level of CO2 in our atmosphere rises, the rate at which heat dissipates into space continues to go down. This has the effect of pushing the climate's equilibrium temperature ever higher.

    In contrast, if we could freeze the rate of waste heat at current levels, it would no longer have a continued effect on our climate's equilibrium level.

    The point is not that waste heat should be ignored, it's that its contribution is minor compared to that of CO2 emissions. In any case, reducing our reliance on fossil fuels would mitigate both issues.
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  14. RSVP, if you do some quick calculations you'll see that waste heat (I assume you're speaking of "cultural heat", heat from nuclear and chemical sources liberated by human activities) is remarkably small compared to heat from insolation, so small that it essentially disappears compared to insolation

    Surface insolation for Earth taking into account angle of incidence, atmospheric attenuation, diurnal cycle etc. is roughly 250MW/km2. The surface of the Earth is about 510,000,000 km2. So, about 127,500TW of total insolation.

    As a basis of comparison, the present total electrical generation capacity of our global attempt at civilization is about 16TW.
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  15. The waste heat argument is not really on topic for this post. John does not have an "Argument" post for waste heat, but he does have a set of links for it, with at least one good article linked there. I think everybody should stop commenting about that topic here, but should pitch in by suggesting additions to that Links page if you've got relevant material.
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  16. RSVP, you bring up thermal emissions and their contributions to global temperatures; keep in mind that GHG's change the steady state condition of the Earth's temps, not just the current temps. If the Earth's temp rises above steady state values, it will lose more energy to space (long wave IR energy) than we gain from the sun, and the temps will drop. Industrial thermal energy is not cumulative over the long term.

    In fact, if industrial heat contributions were the main cause of global warming, the energy imbalance at the top of the atmosphere would be positive - more energy coming from the earth than it receives, as the Earth tried to return to a steady state condition. That's NOT the case: A negative imbalance indicates energy trapping, not energy production, and that should invalidate the industrial energy->global warming hypothesis.
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  17. e at 05:55 AM, re "As the level of CO2 in our atmosphere rises, the rate at which heat dissipates into space continues to go down."
    That rate is not directly because of the CO2, but because of the water vapour which responds directly to temperature, and also absorbs and transmits IR radiation over a much wider band than CO2 or any other greenhouse gas.
    If CO2 has been calculated as having a long residency time, what is the residency time of water vapour. Even though there is a high turnover of individual molecules, water vapour as a gas has residency time beyond measurement, a permanent presence that will exist whilst warmth from any source rises from the earth's surface.
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  18. doug_bostrom at 06:08 AM, I think the point being made is that the average annual heat energy input from energy consumption, about 0.027W/m2, is large compared to the heat energy prevented from escaping for the additional 2ppm of CO2 added annually which is about 0.0075W/m2.
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  19. That figure 0.027W/m2 was based on 2002 energy figure of 13.76TW. If that is now 16TW, the 0.027W/m2 would now be 0.031W/m2.
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  20. "Shaviv and Veizer (2003) "

    Try looking at earlier assessment reports where odd stuff is discussed and discounted on basis on new research. It's not revisited in later Assessment reports unless there is new papers.
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  21. Pointless comparison.

    Here's a handy picture, so we can see what we're really talking about:

    How does "about 0.027W/m2" stack up, compared to additional C02?

    Please, enough on this. It's cooked.
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  22. "By the way, the issue of whether waste heat is an important factor in global warming is one of the questions most commonly asked by students who are first learning about energy budgets and climate change. So, there are no shortage of places where you can learn about this sort of thing."
    Ray Pierrehumbert

    by the way, you have the number for the 2 ppm forcing wrong, at least at current CO2 level. You didn't like the aproximate formula I gave you but definitely you should use it.
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  23. Riccardo at 07:40 AM, as you know I asked for confirmation of the figure, nobody has come up with a different figure yet.
    If you have a different value please don't keep it a secret.
    The formula that yielded the value I posted is current forcing = log2(1+2/385)W/m2 based on 385ppm adding 2ppm annually.
    You can find it here.
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  24. johnd, re "That rate is not directly because of the CO2, but because of the water vapour which responds directly to temperature"

    Not so, CO2 is also a greenhouse gas albeit a less powerful one. This is how the feedback cycle starts in the first place.

    In any case, as you stated, water vapour acts as a feedback due to any increase in temperatures. The size of the feedback is relative to the size of the increase. Waste heat only increases earth's temperature relative to the increase in the amount of waste heat from one year to the next. A constant rate of waste heat will be quickly balanced out by heat dissipation to space and contribute nothing new to warming. So to estimate how much waste heat contributes to warming, you need to look at how much the rate of waste heat has increased, not how much total heat has been pumped out. This is different than CO2, where every extra molecule of CO2 essentially increases the warming rate. As a result, CO2 emissions have a cumulative effect year to year.

    In short, the key difference is: when you look at waste heat, you're looking directly at the amount of heat added to the climate. When you're looking at CO2 emissions, you're looking at an increase in the rate of heat being added to the climate.
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  25. 71.doug_bostrom

    Where is clouds on your image?
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  26. HR - clouds are a response/feedback not a forcing. Unless someone can find a way to make clouds independent of temperature and aerosols. If the GCR hypothesis was proved, then that could be a way but so far no go there.
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  27. HumanityRules, as scaddenp notes clouds aren't a forcing. However, there's a very, very well written discussion of forcings and feedbacks -- including clouds -- at Chris Colose's place. Check it out!

    The very short version of the answer is that uncertainty about clouds is responsible for much of the gap between low vs. high estimates of climate sensitivity (i.e., 2.5 vs 4.5 C).
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  28. 73 johnd

    I followed your link. You should read more closely. That 0.0075 value is measure of the rate of change of CO2 in the atmosphere relative to a doubling. It does not have W/m2/year units at all but units of 2xCO2/year.

    The same link suggests calculating the forcing per relative change in CO2 concentration as described in the post you cite as =5.35 ln(C1/C0) - exactly the same as a previous post. The calculation of this on a year by year increment basis makes no sense for comparison with waste heat production rate, as others have stated. One is an increase in the rate of a rate, and the other is just a rate. It's not like we can pretend that CO2 we put up in the past isn't there and isn't doing anything.

    Why do you discount all the evidence people here were providing rather that go back and checking to see if you read right?
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  29. I meant the "increase of a rate"! This is too loopy.
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  30. Stephen Baines at 11:32 AM, perhaps you can explain the difference between 2xCO2/year and W/m2/year.
    My original read of the link revealed this clarification:-
    "It is a common convention in the literature to use 2xCO2 as the unit for forcing, rather than W/m2"
    I double checked and I did read that right.

    I assume that you also read it as it did not require a particulary close read to come across it. That leaves the possibility
    that the units cannot be exchanged in this application.
    Perhaps you can explain why that might be the case.
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  31. Clouds have -what- to do with the comparison of human-liberated waste heat and C02 forcing?

    Changing topics, much?
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  32. CBDunkerson wrote:

    "Using the actual CO2 figures for today vs 100 years ago gives ln(387/300)=0.367371 C warming... as opposed to the ~0.7 C actually observed. Ergo, we have observed more warming than can be explained by the enhanced CO2 greenhouse effect. Thus demonstrating that total feedback effects over the past hundred years have been positive."

    Wouldn't that be the case only if anthropogenic CO2 were the only change in forcing? IIRC the IPCC report attributes most of the warming of the first half of the 20th century to changes in solar forcing. So the difference between the 0.7C and 0.36C could simply be due to changes in other forcing, rather than being the consequence of feedback.

    Don't get me wrong, I am confident in the ability of the climatologists, and the bulk of the evidence gives little support to low sensitivity, although I keep an open mind on it - and await Roy Spencers new paper.
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  33. johnd,
    2xCO2 correspond to about 3.7 W/m2. Multiply that number by 0.0075 and you'll get the forcing in W/m2 (0.028 W/m2) which is obviously the same you'd get using the formula i gave you before. It's just a simple change of the unit of measure.
    But again, this is not the main problem with your reasoning. You're still missing that the forcing due to increased absorption need to be summed up over time, waste heat does not.
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  34. doug_bostrom
    "surface of the Earth is about 510,000,000 km2. So, about 127,500TW of total insolation"

    You are taking the total surface area. Only one side of the Earth gets Sun at any given time, so you will need to at least half that result for starters and reduce some more to account for albedo.

    In any case, the absolute amount of insolation is supposedly a non-issue (neither here nor there) for those that base their analysis on the radiative forcing model (the tree graph that has branches going left and right). Its funny how the total solar insolation is never mentioned in that context, only when the question of waste heat is brought up.
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  35. RSVP at 18:58 PM on 12 May, 2010

    RSVP, doug has already corrected for a spherical Earth, angle of incidence, albedo. The TOA average solar radiation is 1,366 W.m-2. If you divide by 4 to account for a spherical Earth, and multiply by 0.7 - 0.8 to account for the Earth's albedo, the surface solar radiation is around 250 W.m-2 averaged over the Earth's surface.

    Please stop these tedious attempts to pursue false arguments based on ignorance. You've been here long enough to have learned some basic backround information on these subjects. The idea that a straightforwad subject like the contribution of waste heat to the Earth's energy balance has to be gnawed over by a boring recapitulation of the whole theory and empirical knowledge of radiative forcing and energy balance, as if the subject has only just been awakened and needs to be sorted out fom scratch on this thread is tedious in the extreme.

    Several useful sources of info on this have been posted aready on this thread - please go and read them...
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  36. Dikran Marsupial #82, true. Looking only at CO2 oversimplifies the issue considerably. However, if you look at the chart doug provided in #71 you'll see that various other forcings (including solar) are comparatively minor and largely cancel each other out. If all the uncertainty bands came out with the highest possible result for each forcing that would just about equal the observed warming... but that isn't possible because parts of those uncertainty bands are from overlapping sources. For instance, we know that sulfate aerosols have a strong cooling effect, but we aren't sure how much of that is directly from the sulfates and how much is indirectly from compounds they form... so both forcings have large uncertainty bands, but they can't both be the highest (i.e. closest to zero) value.

    In short, the observed warming can't be explained even when we include all the known forcings... leaving unknown forcings or feedback effects to explain the difference. And we KNOW feedback effects are taking place because we can measure the change in albedo from ice retreat and the increase in water vapor from rising temperatures.
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  37. I agree with Dikran Marsupial that one can't draw conclusions about climate sensitivity by looking just at CO2 and temperature over the first half of the 20th century, since there were countervailing trends in other forcings. Here's a handy figure from Meehl et al 2004:

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  38. chris
    Waste heat is perfectly tangible, unlike the indirect and complex effects of anthropogenic greenhouse gases. The fact that it is so easily calculated demonstrates how tangible it is.

    Waste heat goes directly into oceans and rivers (and the air) everyday, 24 hours a day. Power plants are water cooled for the most part, and the atmosphere does not get a chance to see this heat until it is exchanged at sea. Waste heat is real and accumulating, and yet somehow considered an inconvenient piece of data that is best ignored.

    I am not denying effects of GHGs, but it would be a useful exercise to assume a zero contribution of anthropogenic GHG (for the exercise) just to estimate how this alone would affect temperatures (assuming it is accumulating in some percentage). And in comparing to the actual average global temperature increase, this would help determine how much is actually due to anthropogenic GHGs.

    You comment that the higher the temperature, the more IR. I agree, but this applies to all forms of forcing, and is basically a form of negative feedback which maintains temperature convergence (to the benefit of all).
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  39. RSVP writes: Waste heat is perfectly tangible, unlike the indirect and complex effects of anthropogenic greenhouse gases. The fact that it is so easily calculated demonstrates how tangible it is.

    There's no difference -- heat is heat. Just in one case it starts out concentrated around chimneys, cars, etc. before dispersing, while in the other it's horizontally dispersed throughout the atmosphere right from the start. But the heat created by radiative transfer is every bit as real as the heat created by any other mechanism.

    If you insist on comparing CO2 to waste heat, you should think of the CO2 as equivalent to the machines that produce the waste heat, not the heat itself.

    If you add X joules of heat to the atmosphere, you increase the heat content of the atmosphere by X joules full stop.

    If you build a machine that adds X joules of heat to the atmosphere per year, then you've added X*L joules, where L is the lifespan of the machine in years.

    Likewise, when you add CO2 to the atmosphere, you're essentially creating lots of tiny machines that add X joules every year, and that will keep doing so for roughly a century or so. And every year we create more of these machines ...
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  40. Oh, yes ... I forgot to add this:

    You write "The fact that [waste heat] is so easily calculated demonstrates how tangible it is."

    But it's much easier to calculate the heat added to the atmosphere from greenhouse gases than it is to figure out the total of all sources of waste heat! The complexity in predicting radiatively forced climate change is not in the initial heat transfer, it's in all the various feedbacks.
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  41. Ned
    "Likewise, when you add CO2 to the atmosphere, you're essentially creating lots of tiny machines that add X joules every year,.."

    Well put. I understand the "theory"; however, there is no theory required to quantify waste heat.
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  42. RSVP It doesn't matter that it is more tangible. Imagine a bar for a waste heat forcing of 0.027 W/m2 on the forcing graph Doug Bostrom shows above. You would have a hard time even distinguishing it from 0. It's just not enough heat to matter much.
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  43. RSVP writes: "I understand the "theory"; however, there is no theory required to quantify waste heat. "

    There's no theory required to quantify the absorption of longwave radiation by CO2 either. You can measure it in the lab. Again, the complicated part is the feedbacks.

    You are verging onto "argument from incredulity". I really think you need to give this up. It's been explained over and over again (not just in this thread) that waste heat is quantitatively trivial compared to the radiative effects of greenhouse gases. At some point, continuing refusal to engage with the points that are made by so many other people crosses the boundary into trolling.
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  44. If the heat sink for waste heat is water vapour, and water vapour concentration is relative to temperature, would not the increased water vapour due to that waste heat in effect accumulate the waste heat even if it is relatively small.
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  45. johnd,

    Talking about water vapour just confuses the question. You can compare the relative significance of waste heat vs. CO2 by measuring both of their effects on temperature without any feedbacks. Taking feedbacks into account just multiplies both sides of the equation by the same number.

    The rate vs. increase of a rate thing has been explained in pretty much every way possible. If it is still unclear, please try and re-read and see if one of the explanations sinks in. I don't think much more can be said on this thread.
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  46. johnd, now you're talking about feedbacks, all of which apply to both the radiative forcing from CO2 and the (much smaller) forcing from waste heat. There's the water vapor feedback, the ice albedo feedback, the tundra/forest albedo feedback, etc. All of which will be very small for a very small forcing (waste heat) and much larger for a much larger forcing (absorption of IR by GHGs).
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    Moderator Response: Indeed, the off topic of waste heat has been discussed enough on this thread. Further comments on that topic probably will be deleted from this thread. But please do suggest links to other treatments of that topic.
  47. Ned
    And aside from the question of what is causing global warming, you remark that the effects of CO2 will linger for 200 years even if CO2 levels were to stabilize. Assuming that the Earth's temperature were to actually increase 4 degrees 200 years from now. And assuming GHG did return to "normal" (say 250 ppm). What exactly should cause the Earth's temperature to come back to "normal", assuming all else being equal? Shouldnt it remain higher if equilibrium is maintained?
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  48. John
    Why isnt waste heat in the list of skeptical arguments?
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    Moderator Response: Not enough time to have written pages for all the arguments. The Links contain more. (Click the "Links" button in the horizontal bar at the top of the page.)
  49. Ring-a-ding! Teachable moment.

    What I said:

    Surface insolation for Earth taking into account angle of incidence, atmospheric attenuation, diurnal cycle etc. is roughly 250MW/km2. The surface of the Earth is about 510,000,000 km2. So, about 127,500TW of total insolation.

    What RSVP perceived and concluded:

    "surface of the Earth is about 510,000,000 km2. So, about 127,500TW of total insolation"

    You are taking the total surface area. Only one side of the Earth gets Sun at any given time, so you will need to at least half that result for starters and reduce some more to account for albedo.

    If we take the time to read a little more carefully and integrate new information, more progress in understanding becomes possible.
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  50. RSVP,

    Long term processes such as rock weathering eventually start to remove CO2 from the atmosphere. As CO2 decreases the equilibrium temperature gets pushed down and the earth cools.
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