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Simple Question, Simple Answer… Not

Filed under: — group @ 8 September 2008 - (Français) (Japanese) (Finnish) (Czech)

Guest commentary by Spencer R. Weart, American Institute of Physics

I often get emails from scientifically trained people who are looking for a straightforward calculation of the global warming that greenhouse gas emissions will bring. What are the physics equations and data on gases that predict just how far the temperature will rise? A natural question, when public expositions of the greenhouse effect usually present it as a matter of elementary physics. These people, typically senior engineers, get suspicious when experts seem to evade their question. Some try to work out the answer themselves (Lord Monckton for example) and complain that the experts dismiss their beautiful logic.

The engineers’ demand that the case for dangerous global warming be proved with a page or so of equations does sound reasonable, and it has a long history. The history reveals how the nature of the climate system inevitably betrays a lover of simple answers.

The simplest approach to calculating the Earth’s surface temperature would be to treat the atmosphere as a single uniform slab, like a pane of glass suspended above the surface (much as we see in elementary explanations of the “greenhouse” effect). But the equations do not yield a number for global warming that is even remotely plausible. You can’t work with an average, squashing together the way heat radiation goes through the dense, warm, humid lower atmosphere with the way it goes through the thin, cold, dry upper atmosphere. Already in the 19th century, physicists moved on to a “one-dimensional” model. That is, they pretended that the atmosphere was the same everywhere around the planet, and studied how radiation was transmitted or absorbed as it went up or down through a column of air stretching from ground level to the top of the atmosphere. This is the study of “radiative transfer,” an elegant and difficult branch of theory. You would figure how sunlight passed through each layer of the atmosphere to the surface, and how the heat energy that was radiated back up from the surface heated up each layer, and was shuttled back and forth among the layers, or escaped into space.

When students learn physics, they are taught about many simple systems that bow to the power of a few laws, yielding wonderfully precise answers: a page or so of equations and you’re done. Teachers rarely point out that these systems are plucked from a far larger set of systems that are mostly nowhere near so tractable. The one-dimensional atmospheric model can’t be solved with a page of mathematics. You have to divide the column of air into a set of levels, get out your pencil or computer, and calculate what happens at each level. Worse, carbon dioxide and water vapor (the two main greenhouse gases) absorb and scatter differently at different wavelengths. So you have to make the same long set of calculations repeatedly, once for each section of the radiation spectrum.

It was not until the 1950s that scientists had both good data on the absorption of infrared radiation, and digital computers that could speed through the multitudinous calculations. Gilbert N. Plass used the data and computers to demonstrate that adding carbon dioxide to a column of air would raise the surface temperature. But nobody believed the precise number he calculated (2.5ºC of warming if the level of CO2 doubled). Critics pointed out that he had ignored a number of crucial effects. First of all, if global temperature started to rise, the atmosphere would contain more water vapor. Its own greenhouse effect would make for more warming. On the other hand, with more water vapor wouldn’t there be more clouds? And wouldn’t those shade the planet and make for less warming? Neither Plass nor anyone before him had tried to calculate changes in cloudiness. (For details and references see this history site.)

Fritz Möller followed up with a pioneering computation that took into account the increase of absolute humidity with temperature. Oops… his results showed a monstrous feedback. As the humidity rose, the water vapor would add its greenhouse effect, and the temperature might soar. The model could give an almost arbitrarily high temperature! This weird result stimulated Syukuro Manabe to develop a more realistic one-dimensional model. He included in his column of air the way convective updrafts carry heat up from the surface, a basic process that nearly every earlier calculation had failed to take into account. It was no wonder Möller’s surface had heated up without limit: his model had not used the fact that hot air would rise. Manabe also worked up a rough calculation for the effects of clouds. By 1967, in collaboration with Richard Wetherald, he was ready to see what might result from raising the level of CO2. Their model predicted that if the amount of CO2 doubled, global temperature would rise roughly two degrees C. This was probably the first paper to convince many scientists that they needed to think seriously about greenhouse warming. The computation was, so to speak, a “proof of principle.”

But it would do little good to present a copy of the Manabe-Wetherald paper to a senior engineer who demands a proof that global warming is a problem. The paper gives only a sketch of complex and lengthy computations that take place, so to speak, offstage. And nobody at the time or since would trust the paper’s numbers as a precise prediction. There were still too many important factors that the model did not include. For example, it was only in the 1970s that scientists realized they had to take into account how smoke, dust and other aerosols from human activity interact with radiation, and how the aerosols affect cloudiness as well. And so on and so forth.

The greenhouse problem was not the first time climatologists hit this wall. Consider, for example, attempts to calculate the trade winds, a simple and important feature of the atmosphere. For generations, theorists wrote down the basic equations for fluid flow and heat transfer on the surface of a rotating sphere, aiming to produce a precise description of our planet’s structure of convective cells and winds in a few lines of equations… or a few pages… or a few dozen pages. They always failed. It was only with the advent of powerful digital computers in the 1960s that people were able to solve the problem through millions of numerical computations. If someone asks for an “explanation” of the trade winds, we can wave our hands and talk about tropical heating, the rotation of the earth and baroclinic instability. But if we are pressed for details with actual numbers, we can do no more than dump a truckload of printouts showing all the arithmetic computations.

I’m not saying we don’t understand the greenhouse effect. We understand the basic physics just fine, and can explain it in a minute to a curious non-scientist. (Like this: greenhouse gases let sunlight through to the Earth’s surface, which gets warm; the surface sends infrared radiation back up, which is absorbed by the gases at various levels and warms up the air; the air radiates some of this energy back to the surface, keeping it warmer than it would be without the gases.) For a scientist, you can give a technical explanation in a few paragraphs. But if you want to get reliable numbers – if you want to know whether raising the level of greenhouse gases will bring a trivial warming or a catastrophe – you have to figure in humidity, convection, aerosol pollution, and a pile of other features of the climate system, all fitted together in lengthy computer runs.

Physics is rich in phenomena that are simple in appearance but cannot be calculated in simple terms. Global warming is like that. People may yearn for a short, clear way to predict how much warming we are likely to face. Alas, no such simple calculation exists. The actual temperature rise is an emergent property resulting from interactions among hundreds of factors. People who refuse to acknowledge that complexity should not be surprised when their demands for an easy calculation go unanswered.

623 Responses to “Simple Question, Simple Answer… Not”

  1. 251

    mugwump writes:

    I am suggesting that if we just want to know what climate sensitivity is, maybe there’s an easier way to get that than modeling the entire climate.

    Yo! Mugwump! For about the fifth time, the paleoclimate data doesn’t depend on GCMs, and it gives a climate sensitivity around 3 K per doubling of CO2! For Lindzen’s estimate to be right, you have to explain not only why the models are wrong, but why the paleoclimate data are also wrong. Good luck with that.

  2. 252

    Dan Hughes writes:

    it is highly unlikely that any of the codes utilize the basic fundamental equations of fluid motions; let’s call them the Navier-Stokes equations.

    Actually, I think they do.

    [Response: In the free troposphere, they actually use what are called the primitive equations which don’t include viscosity (since that term is very small). But Dan knows all this. – gavin]

  3. 253

    Lawrence McLean writes:

    Is there any long term data regarding the behavior of the night sky radiation effect?

    For those who do not know, the night sky radiation effect describes the process when a surface exposed to the night sky cools below the surrounding temperature.

    In itself, a trend towards reduction in the temperature differential would be pretty close to proof for increases in the Greenhouse effect.

    The diurnal temperature difference has decreased. Nighttime temperatures are rising faster than daytime — one more bit of proof that it’s greenhouse gases and not the sun.

  4. 254
    Richard Sycamore says:

    Gavin chooses to reply to #56 and #57, but not #54:

    “I know how easy it is to overfit when you snoop the test data. In fact, we don’t consider a model validated until we’ve tested it against completely unseen data. Climate modelers have spent years tweaking heavily parameterized models against a very limited set of data. They are almost guaranteed to have overfit.”

    The true test of overfit is: do we see evidence of a divergence over time between predicted and observed? Consider:

    -When tropical tropospheric temperatures are observed to not fit the model’s predicitons it’s suggested that it’s because windshear was neglected and the tropical data are sparse.
    -When global mean temperature fails to rise from 2001-2008 it’s because the capacity of the oceans to absorb that heat was underestimated.

    I’m not saying all the ad hoc revisionism isn’t justified. Just that I wish it weren’t so necessary. It looks bad. For every divergence, there’s an easy fix. When you assert the physics are “known”, and then are forced to make these post-hoc adjustments to the models, it only adds to the weight of #54.

    Maybe it is better to just admit that the physics are not fully “known”, that many parameters are necessarily guessed at?

  5. 255
  6. 256
    Chris Dudley says:

    John Mashey (#237),

    The value of the big bang theory is that it is fruitful. Hoyle, who has passed away now, was able to present explanations for the evidence that is often taken in support of the theory so he was certainly not rejecting evidence. He was rejecting the big bang on philosophical grounds, grounds that have been very useful in the development of philosophy. Those who feel that existance implies a creator are in some sense anti-copernican. The way for Hoyle to exclude the need for a creator and preserve the very useful vantage that we exist in no special circumstance that Hoyle preferred was to have the universe have no beginning and thus no creator. The fruitfulness of the big bang theory, that it made testable predictions which were supported by subsequent observation, was not persuasive for Hoyle because the big bang semed like it implied magic and thus was not science.

    Hoyle was mistaken there. While it could well be the case that God requires science of us, science cannot require God of the universe no matter how the science is framed. The big bang theory cannot be proof of the existance of a creator because science seeks natural explanations. So, Hoyle’s fundemental error, one shared with Newton and perhaps Einstein was the idea that the existance of a creator could be inferred from His work through science. Had he realized that neither big bang nor steady state theories could speak to the issue and still be science then he might have come down another way. After all, his work had shown that Democritus’ atoms were not, in general, eternal but rather build up in stars through a subtle resonance he discovered in the nuclear physics of carbon.

    While the field of cosmology today is becoming more quanitative, its orgins are deeply entwined with philosphical (pure reason) enquiries and Hoyle’s approach seems tied to this. Anthropogenic global warming deniers have a more difficult task since they need to deny long settled physics to make their case. They thus tend to lack the intellectual rigor or honesty or both that Hoyle required of himself. Comparing them to Hoyle seems an insult to the man.

  7. 257

    If you are interested in climate change, you are invited to contribute to

    Together we want to come up with a coherent theory of climate change incorporating all scientific findings concerning the issue.

  8. 258
    Rod B says:

    Barton (251) your certainty of conclusion significantly exceeds the certainty of the paleoclimate data. I’m not saying you’re wrong, but that you can’t totally exclude other conclusions with a wave of the hand.

  9. 259
    dhogaza says:

    When tropical tropospheric temperatures are observed to not fit the model’s predicitons it’s suggested that it’s because windshear was neglected and the tropical data are sparse.

    Well, both are true. That’s not “revisionism” – the lack of data’s been known forever, and that which exists known to have problems.

    You’re suggesting that a model’s failing to fit bad data is a problem with the model? How quaint.

    -When global mean temperature fails to rise from 2001-2008 it’s because the capacity of the oceans to absorb that heat was underestimated.

    No one serious says this. Congrats on building and burning that strawman.

    You need to read this. Seriously. And also go bone up on noise vs. signal, etc.

  10. 260
    Ray Ladbury says:

    Rod B. How do you have “heat” without having “energy”?

    WRT scientific consensus–this is based on my experience. I know from my experience and my study of science and history of science that consensus is real and important. I also know that scientists rarely if ever really talk about it or talk about what there is and is not consensus on. In effect, they vote by deciding what is and is not worth their effort–what has the best chance of advancing their career, and so the science.

    Oracle of ReCAPTCHA: stress police–must be a CA thing.

  11. 261
    Rod B says:

    Hank (251), thanks for the links. It still seems funny (actually meaning I don’t yet fully understand and need to do more study; anyway….). One Pierrehumbert article says CO2 (then dry ice) came first (on Mars) causing the surface to heat enough to support water. He implies it was first water vapor on Venus that got things near the Kombayashi–Ingersoll limit which created the near runaway temp increase which in turn destroyed the water vapor (exactly how I haven’t gleaned yet) which then cut out the CO2 sequestering through weathering. CO2 increases were last in the chain — a result of runaway warming, not a cause.

  12. 262
    Rod B says:

    Chris D (256): Let’s see. AGW sceptics lack intellectual vigor and honesty because we “just believe” something other from the consensus, as opposed to Hoyle, who (presumably) had intellectual vigor and honesty because he philosophically believed something other than the consensus. One must contemplate this a bit….

    The original contention was that there are respected scientists who have disagreed with accepted dogma. Hoyle viz-a-viz the Big Bang (though as I understand he coined that term) a salient example. (He still may be correct. The fact that a theory, like Big Bang, is helpful and fruitful doesn’t ipso facto make it true.)

  13. 263
    Rod B says:

    Ray, true, you can not have “heat” without “energy”. But you can have “energy” without “heat.”

    I fully agree with your assessment of “consensus” in #260. Doesn’t mean that it is automatically correct. And shouldn’t be cause for prohibiting contrary views, which you implied in #213 though backed off from in #219.

  14. 264
    Ellis says:


    For about the fifth time, the paleoclimate data doesn’t depend on GCMs, and it gives a climate sensitivity around 3 K per doubling of CO2! For Lindzen’s estimate to be right, you have to explain not only why the models are wrong, but why the paleoclimate data are also wrong. Good luck with that.

    I will note this passage from Dr. Rind,

    “Ironically, when we look at paleoclimates, both the cold climates of the Ice Ages, and the warm climates of the Tertiary (from 65 to 2.5 million years ago), the same uncertainty exists. We do not know how cold/warm the tropics were at these times, nor can we properly reproduce the high latitude responses from these climates in our models. The tropical paleoclimate proxies are conflicting and may be misinterpreted; the high latitude responses may be arising under different circumstances. So we cannot use paleo-observations to determine which, if any, of our models has the proper sensitivity in these regions — and in fact, models cannot reproduce what at face value seem to be the extreme changes in low-to-high latitudinal gradients suggested by paleo-data.”

    [Response: Note that he is talking about latitudinal gradients and of periods for which forcings and responses are ill-defined. None of that is relevant to the LGM – and that’s the paleo period that simply isn’t consistent with a negligible sensitivity. (You might care to note that Rind and Peteet (1985) was one of the key papers demonstrating that tropical ocean temperatures must have indeed changed substantially at the LGM). – gavin]

  15. 265
    Jonick Radge says:


    “I usually don’t bother responding.”

    Yes you do. This response tells me at least more than I want to know.

    “There’s no way of saying this without sounding obnoxious, but since you showed me yours, I’ll show you mine.”

    Ugh! You’re right. But if you’re going to open that door you might as well commit to it and give your name so that we can begin to examine your credentials in detail. Otherwise, please lay off the privates.

    “…Al Gore (and the alarmist industry in general)…”
    “…Unfortunately, those pushing the alarmist agenda are using the higher sensitivity estimates from the models to further their political goals…”
    “…I don’t believe in this idea of ‘consensus science’…”
    “…invoked to justify all kinds of crazy alarmist nonsense…”
    “…concerning his unrequited love affair with Al Gore…”
    “..There are plenty of respected scientists that do not buy into your consensus…”

    Well OK. Since a theme here seems to be how professions outside of the climate community approach the science, I can’t help wondering about the language. This is rhetoric straight from the stocks of partisan hacks. Why would anyone seriously trying to pass as a iconoclast lean on this kind of down scale (‘down scale’ for this forum) verbiage?

    There are all kinds of activity embedded in these phrases, including a fuzzing of the boundary issues between science, policy making, and politics. If you’re concerned about ‘firewall’ issues, then why not discuss them openly without all the thinly veiled condescension? It is ironic since this is precisely the kind of framing language that’s designed to provide cover for the nihilistic corrosion of systems informing public policy.

    Just some general thoughts about studying natural science for whomever.

    You need to be firing on all cylinders to begin to grasp the breadth of any of the earth sciences. While analysis is certainly the bedrock, strong visualization skills are also required to properly contextuallize information about large natural systems — literally to keep odd scales in perspective, proportion, and interconnected. It’s a little like the medieval scholars who performed prodigious feats of memory by visualizing a castle and carefully stocking it with information.

    Want to test yourself? For inspiration try out this extreme exercise: Some of the old masters’ knowledge of anatomy was so strong that they could, with great veracity and subtlety, draw the human form in any position without using a model. Most of us can barely manage stick figures. Yet stick figure science is the stock and trade of so many skeptics, a hodgepodge of poorly related, highly embellished elements.

    Climate science is big science. It’s a group effort. People skills count. Being brilliant is a necessary but, after a point, not a sufficient condition if you’re too prone to being a destructive influence.

  16. 266
    mugwump says:

    BPL #251:

    Yo! Mugwump! For about the fifth time, the paleoclimate data doesn’t depend on GCMs, and it gives a climate sensitivity around 3 K per doubling of CO2

    In which case the best estimate for sensitivity should be 3 +- a small number. It’s not, so the certainty you express is not a “consensus” view.

    As for the paleo stuff, I asked this question above but it bears repeating: what’s the justification for assuming the sensitivity is linear?

    To elaborate: the paleo results are roughly that we saw a 6K rise for a total 6W/m2 increase in forcing from the LGM to the Holocene, therefore climate sensitivity is 1K/W/m2 (= 6K / 6W/m2). But the climate today is very different from the climate at the last LGM. We would not necessarily expect a 1W/m2 increase in forcing to have the same impact today as it had back then. Or in mathematical terms, climate sensitivity may be a nonlinear function of forcing and temperature.

    To elaborate even more, consider a completely hypothetical case: that of a snowball earth well below the “thaw” point. Assume an increase of 1W/m2 of forcing would not be sufficient to melt the ice, and hence there would be no albedo feedback. Maybe a snowball earth has very little cloud to speak of either, so the cloud feedbacks are negligible. Since the oceans are mostly covered with ice, increasing their temperature is not going to result in much CO2 outgassing, so we won’t see a CO2 feedback either. So the snowball earth may have a climate sensitivity close to the no-feedback case of about 0.3K/W/m2.

    Now, what if the Earth gets close enough to the sun to increase forcing above the snowball earth thaw limit? Maybe that’s as little as 3W/m2. All the feedbacks will start to come into play, and we’ll see a rapid (in geological terms) temperature rise. If the temperature rises 6K (remember, this is all hypothetical), and we attribute an extra 3W/m2 forcing to the albedo and CO2 changes (and whatever else – aerosols etc) then using the paleo sensitivity argument we’d say the climate sensitivity is 1K/W/m2 ( 6K / [3W/m2 + 3W/m2] ).

    Finally, once the earth has heated up again, cloud dynamics may yield negative feedbacks, which bring the sensitivity back down again.

    So depending on the state of the earth, sensitivity to a given amount of forcing may vary. The sensitivity you get by looking at changes from the LGM to the present may not be the same as the climate sensitivity due to increased CO2 today. Or at least if we think it is, I am curious as to why.

  17. 267
    mugwump says:

    RE #265:

    Why would anyone seriously trying to pass as a iconoclast lean on this kind of down scale (’down scale’ for this forum) verbiage?

    A) it’s no more downscale than the verbiage used to describe sceptics;

    B) it’s true: high sensitivities are used to push alarmist agendas;

    C) I don’t lean on it.

  18. 268
    Steve Reynolds says:

    gavin: “…the LGM. Explain that away using a sensitivity of less than 2 C and then we can talk.”

    As was mentioned in 247, how do we know climate sensitivity is the same now as during the LGM?

    Would we not expect the amount of albedo feedback to have been greater when snow/ice were at lower latitudes? Maybe the LGM value should be considered an upper bound?

  19. 269
    Dave Andrews says:


    not a sufficient condition if you’re too prone to being a destructive influence

    What exactly do you mean by this?

  20. 270
    dhogaza says:

    Would we not expect the amount of albedo feedback to have been greater when snow/ice were at lower latitudes?

    Obviously, the scientific community has never thought about this. As evidence of their idiocy I submit this abstract:

    The contributions of expanded continental ice, reduced atmospheric CO2, and changes in land albedo to the maintenance of the climate of the last glacial maximum (LGM) are examined…

    You could’ve spent 30 seconds in google scholar yourself.

    Then I’d could’ve spent that 30 seconds doing something else.

    Mugwump’s thinking is equally original, new to the scientific community …

  21. 271
    Jonick Radge says:


    “A) it’s no more downscale than the verbiage used to describe sceptics;”

    My point is it’s stock — as in hackneyed. Why would YOU stoop to using language that works against your own credibility? And your answer seems to be that if you thought Al Gore set his hair on fire and jumped off a bridge, you’d want to do it too.

    “B) it’s true: high sensitivities are used to push alarmist agendas;”

    The key phrase here is “alarmist agendas.” That is purely a political judgment, and since it’s left hanging there, it doesn’t begin to address the way policy actually gets formed. You could have as easily said, “It’s true: low sensitivities are used to push dismissive, industry agendas.” You’d then no doubt be spending your time here trying to finagle higher sensitivities out of the discussion.

    “C) I don’t lean on it.”
    You don’t need to lean on it.

  22. 272
    Jonick Radge says:


    Sorry. That was poorly worded. I was referring to trolling type behaviors mostly. There are probably quite a number things that cross the line of what’s tolerable. Though it’s an extreme example, I’m not sure I’d want to work with someone who was prone to violence, for instance. It’s a judgment call and depends on the situation. You can see it at work here in the way editors handle comments.

  23. 273
    mugwump says:

    RE #270:

    It looks like that paper models the LGM with a (very old) GCM. All well and good, but this discussion is about GCM-free climate sensitivity estimates.

  24. 274
    Lloyd Flack says:

    There have been several comments on the lines of how do we know the climate sensitivity is the same as in the past?

    The GCMs give sensitivities of the form:
    change in temperature is proportional to change in logarithm of CO2 concentration.

    Now if we vary the CO2 concentration over a wide enough range we expect that this relationship will eventually break down. But we are not varying it over a wide range. We do expect sensitivity to have this form over the ranges of CO2 concentration that we have to deal with. We have no reason to expect an discontinuities in the functional relationship between temperature and concentration. We know of nothing that could cause such a discontinuity and we have no evidence of it occurring.

    Now could the constant of proportionality above be different in the past? Well, with a different continental configuration and different vegetation I expect that it would be somewhat different though I don’t know by how much. However we are making comparisons with the Pleistocene when we had a continental configuration and vegetation similar to today. There is no reason to expect more than a minor difference in the constant of proportionality.

    Could the constant of proportionality change with temperature and concentration? I expect that it does change. However I expect that it changes smoothly and if there is only a small change in temperature or concentration I would expect only a small change in the constant of proportionality.

    For sensitivities to be extremely different in the Pleistocene or in the expected future warmer period we would need the physical processes driving temperature changes to be different in ways that we have no reason to believe that they are.

  25. 275
    John Mashey says:

    re: 256 Chris Colose

    “Anthropogenic global warming deniers have a more difficult task since they need to deny long settled physics to make their case. They thus tend to lack the intellectual rigor or honesty or both that Hoyle required of himself. Comparing them to Hoyle seems an insult to the man.”

    I’d said:
    “Obviously, for climate parallels, this is more like “It’s all cosmic rays” than like “Anything but CO2″, i.e., someone seems to have a strong belief in a particular idea that happens to conflict with the mainstream, as opposed to not wanting the mainstream, and being happy to take anything else.”

    I always thought Hoyle was a fine scientist, thought he might fairly have gotten a Nobel. As a kid, I enjoyed a few of his books.

    I thought my wording was clear, but I guess not.

    Even great scientists sometimes fasten on a hypothesis during that period when there are multiple competing hypotheses, and then spend the rest of their lives defending that hypothesis even as overpowering evidence mounts for one of the alternatives. That doesn’t mean they are wrong, but it’s a recognizable pattern. Of course, most scientists change their minds when the evidence has piled up, sooner or later.

    Although there is a vast difference in contribution, from my reading, Hoyle would seem modestly akin to Svensmark (cosmic rays do it)rather than Fred Singer (anything except CO2). Perhaps they’re different in that at one point, steady-state was a more plausible hypothesis than big-bang. I don’t think cosmic rays have ever been a strong candidate to explain GW, although it hasn’t been that long since it’s potential influence was bounded as low as it’s been.

    Put another way, Hoyle’s steady-state and big-bang are mutually contradictory.
    Claiming there is *some* influence from cosmic rays is not mutually contradictory to AGW, but claiming it’s the major influence is.

    Anyway, there was no insult intended to Hoyle.

  26. 276
    dhogaza says:

    It looks like that paper models the LGM with a (very old) GCM. All well and good, but this discussion is about GCM-free climate sensitivity estimates.

    I went and re-read the OP and see no evidence for your claim.

    And I went and re-read the post I responded to, and see no evidence that the question was asked in the context you suggest.

  27. 277
    Chris Dudley says:

    Rob #262,

    I used the term rigor in a fairly technical sense. Hoyle understood the big bang theory very well. Who better? His alternative theory attempted to explain the same observations.

    This situation differs from the situation with deniers. Those who deny CO2 has an effect, if they understood radiative transfer, would realize that they are barking up the wrong tree. That is not the sort of physics it makes much sense to challenge. But, though they don’t understand it, that is essentially their position: that there is something wrong with radiative transfer.

    There are also those who deny the data: that the temperature is increasing. These are even further from Hoyle.

    Fruitful theories gain support because they lead to deeper questions. Questions about grand unification in particle physics stem in part from consideration of the big bang theory as an example. The large hadron collider was recently commissioned to explore some of these questions. So, it remains worthwhile to continue to test the big bang theory whereas less fruitful theories don’t get much further testing. The big bang theory could be wrong in interesting ways while alternatives don’t lead to such a possibility.

  28. 278

    Rod writes:

    Barton, I’m getting OT but I appreciate the helpful info re Venus. Why didn’t Venus’ CO2 get sequestered into carbonate rock?

    Venus, closer to the Sun than Earth, was hot enough for a runaway greenhouse effect to start. Water evaporated from the (hypothetical) early Venus ocean, water vapor is a greenhouse gas, more heat led to more evaporation, until the whole ocean was vaporized. Sunlight dissociated the water vapor, the hydrogen escaped, leaving the oxygen, which combined with the rocks. The temperatures were high enough to cook carbon dioxide out of the rocks.

    On Earth and Mars, the water vapor pressure curve isn’t high enough to go into a runaway state. Google “runaway greenhouse effect” Earth Venus Mars to see some web pages about this, complete with diagrams.

  29. 279

    Chris Dudley writes:

    Anthropogenic global warming deniers have a more difficult task since they need to deny long settled physics to make their case. They thus tend to lack the intellectual rigor or honesty or both that Hoyle required of himself. Comparing them to Hoyle seems an insult to the man.

    Hoyle was a great astrophysicist, at least in the ’40s and ’50s, and a pretty decent SF writer. But he was also a raving crackpot. In addition to denying the Big Bang long past when everybody else had had been forced to accept it, he also believed in creationist arguments about combinatorics and abiogenesis, that interstellar dust grains were bacteria, and that the flu was brought to Earth from space.

  30. 280
    Mark says:

    Rod B #258.

    Additionally you can’t invoke remote possibilities with just handwaving arguments. That’s been used to “confirm” that the LHC is dangerous: we can’t KNOW that it won’t destroy the earth and all the inhabitants, so therefore it is too dangerous to start.

    So why are values outside the range of “reasonable based on limits of current measures and explanation” the REQUIRED resolution? And why only values outside those limits that prove YOUR point the only ones that should be considered?

    No hand waving, please.

    Hard science.

    Do as you demand of others. To do otherwise is hypocrisy.

  31. 281
    Mark says:

    Mugwump, what if instead of being 2 degrees or less (which someone came up with whilst ADMITTING they were ignoring some of the changes [so admitted missing out something that would increase the sensitivity] seen and you have taken as “true”), it is 6 degrees or more?

    Why is it with denialists, even when they are admitting GW, they pick and choose figures to the “we’re A-OK, people!” rather than the “ohshitohshitoshit we’re all going to die!” side? If the models are wrong, why are they wrong in a way that makes it OK for humans to continue? If measurements are wrong, why are they wrong in a way that means business as usual? If models are deficient, why do they only miss out effects that mean there’s no problem?

  32. 282
    wht says:

    This seems frustrating. A few of us work the analysis of Peak Oil depletion and have been able to derive several of the empirically observed relations through relatively simple math derivations. These have been known for around 50 years, descrbed by King Hubbert using heuristics.

  33. 283
    Martin Vermeer says:

    Steve Reynolds #268:

    As was mentioned in 247, how do we know climate sensitivity is the same now as during the LGM?

    God of the Gaps, Steve. You’re on a hopeless errand.

    You see, the climate system doesn’t know where the warming came from. So, if it is from astronomical variations in Solar influx, or from CO2 keeping the warmth from escaping, it will respond in largely the same way.

    See the first picture in

    It shows the response to either an increase in solar intensity, or in CO2 concentration. See how similar they are? (There is an important difference in the stratosphere; it knows CO2 when it sees it and uses it for radiative cooling. But this is inconsequential for the global energy balance.)

    Would we not expect the amount of albedo feedback to have been greater when snow/ice were at lower latitudes? Maybe the LGM value should be considered an upper bound?

    The doubling equilibrium sensitivity is defined by convention not to include ice sheet albedo, for good reasons. It is indeed highly nonlinear to temperature.

    The remaining sensitivity by this definition is assumed to be linear. Of course this assumption could be wrong — but nobody has presented a good reason that it would be… there are several independent observational lines of evidence pointing to a 3C sensitivity, and they are pretty unlikely to be all wrong.

    The Snowball Earth situation is so far out as to be irrelevant for the precise sensitivity of today. Almost like Venus…

    BTW what about the Eemian warming and sea level rise? Those temperatures were similar to our century, though astronomically forced. Why am I wrong to conclude that you cannot pump heat into the climate system by whatever means without getting your feet wet?

  34. 284
    mugwump says:

    RE #274 Lloyd Flack:

    The relationship between CO2 concentration and forcing is unlikely to change, since that depends only on basic physics. But that doesn’t necessarily mean the relationship between forcing and temperature change is constant, since that depends upon the state of the climate itself (see my hypothetical example in #266).

  35. 285
    Chris Dudley says:

    Barton Paul Levenson (#279),

    I find Greenberg and coworkers’ EURECA-B sample of material that was irradiated on orbit to be a better laboratory analog to the insterstellar 3.4 um absorption feature than the Hoyle and Wickramasinghe proposed identification. In fact I use it in Figure 1 here: which should be out next month. On the other hand, investigating the concept of panspermia is something that receives a great deal of NASA attention and funding. The possibility that life on Earth was seeded from Mars or the other way around is under active investigation. Should we say that the Alpher-Bethe-Gamow paper was written by crackpots because it turned out that neutron capture can’t build all of the elements?

    Multiple independent origins of life seem to me to be more likely than galaxy-wide panspermia because highly ordered systems can arise spontaneously in physics. But, since we are working without even a second datum so far, it seems premature to rule out their view yet.

    The case that global warming deniers are crackpots or, often more likely, dishonest stooges, is not supported by calling peer reviewed science, such as that produced by Hoyle, crackpot.

  36. 286
    Ray Ladbury says:

    Mugwump, #266: It would appear that your objection to the models (and presumably to the laws of physics, too) is that they constrain your creativity. Positing hypothetical situations unconstrained by any data or model (and yes models are an inherent part of science) may be fun, but it ain’t science.

    What evidence do you have that the climate sensitivity of the LGM is significantly different than that of the current climate. Volcanic eruptions provide a sensitivity in the same range, as do other sources of data. There aren’t too many forcers that persist on a timescale of decades to millennia other than CO2.

  37. 287
    mugwump says:

    RE Martin #283:

    The doubling equilibrium sensitivity is defined by convention not to include ice sheet albedo, for good reasons. It is indeed highly nonlinear to temperature.

    The paleo argument for doubling CO2 sensitivity is agnostic with respect to forcing source: you simply divide the temperature change by the sum of the forcings to get the expected temperature change per W/m2 of additional forcing. So in that sense it does include ice sheet albedo.

    This article is an easy to read overview. On page 147 there is mentioned the possibility that climate sensitivity may differ between the LGM and today, but that

    “our analysis minimizes that factor by specifying ice sheet area and atmospheric composition as boundary forcings”.

    I am unsure what that means, but hopefully the original source (Lorius et. al.) will illuminate that.

    It is also interesting to note that in the same paragraph the possibility of long-term random climate fluctuations is mentioned:

    “There are many uncertainties and limitations in paleoclimate analyses. For example, chaotic long-term fluctuations in ocean heat transport can contribute to observed global temperature change”

    I wonder how large the authors think those fluctuations can be? MWP anyone?

  38. 288
    Nick Gotts says:

    Re #279 (BPL on Fred Hoyle)
    Hoyle also claimed that the best-known Archaeopteryx fossils (the London and Berlin specimens) were faked, the feathers being stuck on with glue. He ignored the fact that other specimens with feathers are known, and showed considerable ignorance of the processes of lithification. However, it does seem unfair that he did not get a Nobel for his work on stellar chemistry, when two close colleagues did.

  39. 289
    Steve Reynolds says:

    Martin: “…the climate system doesn’t know where the warming came from.”

    I’m not sure why you state that in reply to me, since I wasn’t disputing it; also not sure why you want to bring religion (God of the Gaps) into this.

    “The doubling equilibrium sensitivity is defined by convention not to include ice sheet albedo…”

    I understand that it does not include the long term ice sheet effects, but that does not eliminate albedo effects from seasonal snow at different latitudes with different temperatures.

    As far as the Annan paper that you reference, it is interesting that the LGM evidence he uses has the same or higher probability for climate sensitivity of 1C as for 4.5C!

  40. 290
    Ike Solem says:

    Let’s try and make Spencer Weart’s point again, using a different system and a different model.

    For familiarity’s sake, lets pick a Boeing 747, which is actually a good deal less complicated than the global climate system. They are both similar in that they rely on a steady source of energy – fuel tanks for the Boeing, the Sun for the climate system.

    So, let’s say we build a complex computer model of a Boeing in flight, and we test that model using wind tunnels and model planes. We only work with the actual Boeing 747 – say a 747-8:

    Now, someone comes along and reduces the wing span by eight feet. Now, someone come up with a simple, logical, one-page mathematical proof that the airplane will still be able to take off. Or, find the maximum wing-reduction length that will still allow the airplane to take off from a normal runway. Give me a simple, logical answer that doesn’t involve complex computer models.

    One other thing – you only can extrapolate from the 747-8. You can’t go build a new physical model – a wind tunnel system – nor can you build a 747 with shorter wings and try and get it to takeoff by remote control. That meets the climate system limitations – we don’t have an identical planet with no fossil fuel CO2 emissions to compare ours to.

    Obviously, it is ludicrous to suggest that anyone could answer that Boeing question without having access to state-of-the-art supercomputer models. There is no simple “lift-feedback analysis” that “proves the effect of shortening the wings would be minor and ignorable.” Anyone making such a claim would be met with incredulous hilarity.

    However, all the fossil fuel PR lackeys on this thread would have you believe otherwise. It’s also interesting how they try and convert scientific issues into personal ones – as if it is the “expert” that matters most, not the logical scientific argument.

    See for example, my comment #175, in which I pointed out that the basic conclusions about global warming arrived at in the 1970s still hold up today, with Dave Andrew’s response in #186, where he claims that “the expert” is “skeptical.” He doesn’t quote the expert, he quotes one William Sweet who is talking about the expert… by the way, William Sweet is mostly trying to promote nuclear energy in his book, as “the only climate solution.” See

    That’s really very illustrative, as it shows how PR flacks are unable to use clear scientific arguments to back up their claims, but instead must rely on innuendo, personal attacks and the like.

  41. 291
    Rod B says:

    BPL, then doesn’t that make H2O the high temperature culprit (cause) with Venus, not CO2 as is often said?

  42. 292
    Rod B says:

    Mark (280) my only point was that I thought the vagaries of paleoclimate measurements (by proxy) are sufficient to make conclusions about that period less than absolute certain. I don’t fully comprehend your post; it seems to rebut something I didn’t say. Am I missing it?

  43. 293
    Lawrence Brown says:

    I believe that the climate sensitivity factor is non-linear by definition. To go back to an old cliche- a cinch by the inch, hard by the yard. Looking at Gavin’s “Learning from a simple model” post,the multiplication factor,under the heading Climate Sensitivity, is given as 0.25/sT^3 (where s is the sigma in Stefan’s law), which looks suspiciously like the inverse of the derivative of F(top)= LsT^4(where L is lamda, the emissivity).Therefore dT/dF=1/4sT^3.

    The senisivity, defined in this manner, isn’t linear but is inversely proportional to T to the third power.This example is simplified and feedbacks aren’t taken into account but the basic definition, should be the the same unless I’m making some misintepretation.

  44. 294
    Hank Roberts says:

    > http://beautifulplanetearth
    Bzzzt. Blogspamming?

    > Venus
    Rod, lots of ultraviolet, or a low gravity, both are ways a planet can early on lose much of its hydrogen. H2O gets broken up by ultraviolet into hydrogen and oxygen; hydrogen escapes rapidly into space. Thus Venus (closer to the sun, slightly lower gravity) early on lost much of its hydrogen, precluding longterm presence of much water. It’s in the links above.

  45. 295
    Gareth says:

    One problem with using paleoclimate to derive figures for climate sensitivity is that this does not help us work out what will happen in the future. Assuming that system will respond in the same way as when warming out of an ice age seems to me to be unjustified. The response of the Arctic – the probable (near) future loss of summer sea ice – pushes the climate system into new territory – one we have very few analogues for in paleoclimate.

    Being confident that a tightly defined “sensitivity” falls into a certain range is not the same thing as saying that’s how the climate will respond in the coming century. We really are out into the unknown unknowns – at least until the GCMs can accurately reflect current changes in the Arctic, and we can quantify potential carbon cycle feedbacks.

  46. 296
    Ron Taylor says:

    Re BPL in 253. Lawrence McLean said, in effect, that a decrease in the diurnal temperature range would pretty much verify an increase in AGW. You said that the range has been decreasing, with no further comment.

    I have been trying to follow up on that and my reading indicates that the GCMs predict an increase in the DTR. Maybe I have missed something. I too had always believed that a decrease in the DTR would indicate the presence of AGW, or at least nullify the idea that the source of the warming could be solar. So which is it – is a decrease in DTR an indication of AGW, or not?

  47. 297
    Paul Middents says:

    Mugwump’s search for a one page derivation of climate sensitivity independent of the GCM’s is interesting in its Quixotic fervor. He has a little knowledge as demonstrated when he “showed us his. . . top undergraduate student in theoretical physics and pure mathematics at my university,” and he has read over 70 climate related peer reviewed papers. His questions are perceptive enough to get reasonable responses from Gavin and only a mild slap of the wrist when he gets a little too fervent.

    I thought it would be interesting to go to the source for the even handed estimation of climate sensitivity, James Annan. What should I find upon re-reading his 2006 blog entry but an exchange with our own mugwump that took place in the last few weeks.

    The discussion seems to have terminated abruptly on September 6 after which the mugs took up his quest on Real Climate. Mugs refers to this exchange in #220. James was a little less than gentle. Perhaps that’s what Mugs was referring to above in #54 when he notes disdainful treatment from mainstream bloggers. Read the exchange and see if you think James was unduly harsh. Mugs says his last entry, which was deleted, clarified his position.

    On Sept 9 mugs was directed to the literature on LGM. Two hours later he was back with a diversion to a discussion of Douglass, the subject of his exchange with Annan. Two days later he was referred to Pierrehumbert’s on line text but we got a handwave about how hard it is to concentrate on a text book written for undergrads. Mugs notes that he hasn’t had time yet to look into the LGM. Since then we’ve been treated to more handwaving.

    Until he can address in some substantive way, the evidence of the LGM, perhaps he might desist in his hectoring the grownups.

  48. 298
    Jacob Mack says:

    No model, mathematical, graphical conceptually can possibly take into account every variable and synergystic scenario.Still, more often than not, the IPCC predictions in mdedian range have proven very accurate with acceptable margins for error. Of oourse the 2007 does take into account new data and this is good science. We always want to be able to say where accurate predictions have been made and where there is room for improvement and when emprical data is assessed we must adjust accordingly.

    The Biological evidence for global warming and not just regional fluxuations is enormous at this time.

  49. 299
    Chris Dudley says:

    Nick Gotts #285,

    I wonder too if his strange love for nuclear power is not just a continuation of his disagreement with Sir Martin Ryle. Ryle presented source number counts for radio sources which suggested time evolution in radio source brightness or space density that did not fit well with the steady state theory. The argument appears to have gotten personal. Ryle argued against nuclear power on non-proliferation grounds. Hoyle seems to have taken the opposite position on nuclear power without any clear consideration of the practical difficulties involved in attempting to rely on it.

  50. 300
    Lawrence Coleman says:

    The difficulty in forcasting time-frames for tipping points to occur is that every new report that come to lights shows that we have les and less time than we originally thought. Case in point: the WWF is now calling this year the worst on record for the arctic in terms of melt area and the quality of ice remaining. I saw that coming months ago despite a relatively cool northwern hemisphere this summer. The IPCC scientists better factor in the worse case scenario for the arctic when it comes to predicting effects of CC as that will be much closer to the mark I think.
    The north atlantic current will begin slowing if it hasn’t already due to the lack of cooling ice and the warming of the ocean at the arctic latitudes throwing the entire world’s climate on it’s head. I cannot see a complete stopping of the current due to not enough transient volume of fresh water being released, but a definate slowing down I think is inevitable. How will a slower north atlantic current affect the world’s climate?? By 10%, 20% 30%??