RealClimate logo

The Alsup Aftermath

The presentations from the Climate Science tutorial last month have all been posted (links below), and Myles Allen (the first presenter for the plaintiffs) gives his impression of the events.

Guest Commentary by Myles Allen

A few weeks ago, I had an unusual — and challenging — assignment: providing a one-hour “tutorial” on the basic science of human-induced climate change to a Federal District Court in San Francisco. Judge William Alsup had requested this tutorial to bring him up to speed on the fundamental science before proceedings begin in earnest in a case brought by the cities of San Francisco and Oakland, on behalf of the people of California, against a group of major fossil fuel companies, addressing the costs of climate change caused, they argue, by products those companies have sold.

The format was straightforward — two hours each for the plaintiffs and the defendants, and the judge had provided us with a series of questions on the essential physics that he wanted addressed, as well as requesting a timeline of how our understanding of climate change has evolved over the past 150 years. My presentation was followed by Professors Gary Griggs, showing detailed projections of sea-level rise and its impacts on California, and Don Wuebbles, presenting key findings from the latest US National Climate Science Special Report (also speaking for the plaintiffs). Between Gary and Don, the Court heard from Theodore Boutrous, a lawyer speaking on behalf of Chevron, one of the defendants.

The case was fairly widely covered, (here’s an example) and most of the attention was, understandably, on what the oil companies had to say: the fact that Gary, Don and I agreed with the IPCC was hardly ever likely to be newsworthy. But I’ve had a few requests since about what I presented — including from some students who spotted that a carefully compressed summary of climate change science might be quite handy revision material. So, with exam season nearly upon us, here it is — or at least, here is what I would have presented if I’d got through it all: in preparing this material, I had completely failed to anticipate the number and depth of Judge Alsup’s questions, so we only got as far as the Charney Report.

Prior to the hearing, Andrew Dessler on Twitter, Gavin Schmidt at RealClimate and Oliver Milman at the Guardian all had a crack at the judge’s questions:

I was definitely more ambitious and I go into more detail than Gavin, Andrew and Oliver on how attribution works, partly because that’s what I do, but also because just telling the judge “the IPCC says the warming is pretty much all human-induced and 80% of that is CO2” would have been a bit circular, having been involved myself in those IPCC assessments since the 1990s.

My contribution had its ups and downs — a low point was definitely when Judge Alsup declared “your chart sucks” in response to a powerpoint slide (right) which showed an artist’s impression of the Nimbus 4 satellite at the expense of a graph of how the spectrum of outgoing long wave radiation changed in response to rising greenhouse gases between 1970 and 1997. Frustratingly, the chart he wanted (from John Harries’ 2001 paper) was hidden under the pretty picture, but we were already late and I chickened out of breaking open the powerpoint to move figures around in a live courtroom. But the high point came just a few seconds later, when he asked “so, how much did the temperatures [of carbon dioxide molecules emitting energy to space in those critical wavelengths of the infrared] fall over those 27 years?” — showing that, after only half-an-hour, and despite my obscure charts, he had already got a better grasp of the basic mechanism of the enhanced greenhouse effect than many.

I’ve restored that spectrum to its rightful place in the version below, as well as adding some more material on molecular dipoles at the beginning, since Judge Alsup (and others since) had questions about how it was that carbon dioxide molecules could act on infrared radiation over a much larger volume than the molecules themselves actually occupy. I’ve also added some more material later on to address other questions that came up. The material I actually covered at the time is all available on the court record.

The edited presentation runs for just under 45 minutes, and I’ve broken it up into five segments. I’ve also put up the powerpoint in case you want to use some of the graphics in your own teaching. I hope it’s useful.

Tutorial: The basic science of human-induced climate change

Part 1
Part 2
Part 3
Part 4
Part 5

Presentation: The basic science of human-induced climate change

Text adapted from original post at ECI with permission.

132 Responses to “The Alsup Aftermath”

  1. 51
    Dan DaSilva says:

    48 izen, quote concerning a mistake of science

    “In that case, the consensus was at least partly skewed by the efforts of private enterprise with an economic interest in providing a refined energy source. There was an attempt to minimize and divert any blame for harm caused by its own product.”

    In the case of “global warming” skew is caused by the environmentalist mindset. (Greenpeace comes to mind). I know that many here think that the biggest evil in the world is private corporations but get over it people. If you want to find the evil look to people trying to create a utopia.

    Is it peer review that corrects science mistakes, or is it evidence? You can not find an answer until you have enough evidence. Otherwise, you could answer all questions by just having scientists vote.

    Human nature cannot be fully corrected by peer review, but overwhelming evidence will change minds.

  2. 52
    Dan DaSilva says:

    49 Ray Ladbury

    “A climate scientist might not like that there are positive feedbacks that raise the climate sensitivity above 2.0.”

    Here is an idea for all the climate scientists out there. Run your models with a lower sensitivity. You will not have to fudge the aerosol numbers to get a proper response. (Not my idea, of course, thanks to MIT Professor Richard Lindzen)

    You might become a target of your peers by assuming a lower sensitivity but go for it (The Serengeti Principle, thanks to Dr. Mann). The prize goes to brave.

  3. 53
    Dan DaSilva says:

    49 Ray Ladbury quote:

    “Not once have you done this, and instead, you resort to insinuation, irrational claims, selective use of facts, generalizations, and political comments and the bottom line is you aren’t persuading anyone here. Your claims don’t stand up to scrutiny by the experts.”

    I will admit to the selective use of facts, insinuation, and generalizations. On “irrational claims”, I would like the examples so that I could refute you or correct myself. “political comments” Politics is a driving force in human nature so I do not view that as out of bounds.

    “Not persuading anyone here.” WHY would you think I could POSSIBLY do that? The best anyone can do is think and cause other do so also.

    “Your claims don’t stand up to scrutiny by the experts” Not sure, I would like for experts to give their thoughts here. Maybe I am corresponding with experts. Or possibly they do not think it worth their time, I do not know.

  4. 54
    Dan DaSilva says:

    43 Mac
    “That is a falsehood”
    Yes, I know, this a danger of sarcasm. I will try to steer clear of “sarcasm” in the future.

    ‘But deniers today don’t say that. Instead, they say, “The underlying theory is wrong.’
    I believe the underlying theories. (CO2 causes warming, AGW is happening, etc) Do I still get the denier label? (Not that I care I was wondering if you are consistent)

  5. 55
    Hank Roberts says:


    For all, I really know it could be 150 percent and we would have cooled without CO2.

    Well, well, well. Remarkable insight, and one you can check by looking it up. Congratulations.

  6. 56
  7. 57
    Dan DaSilva says:

    49 Ray Ladbury

    “It is a question of what they have to believe (in terms of facts, models techniques…) to be productive in their field.”

    There are well know climate scientists who have some contrary views how they stay productive?

    Are they deniers?

  8. 58
    Dan DaSilva says:

    My first (or one of the first) experiences at RealClimate I was asked a question by a famous climate scientist (who shall remain nameless). I gave what I thought was a reasonable answer and was promptly put in the borehole.

    However, after that experience, RealClimate has been very fair and I only got tossed in the hole a few times for things that may have deserved it. So as not to abuse that privilege I will refrain from any more comments on this thread. Thanks for the interaction.

  9. 59
    nigelj says:

    Dan De Silva @46, you now say you believe humans are only causing 25 – 50% of global warming and that you “challenged almost everything here”. You started out claiming you believed in the basic consensus on agw, so you simply can’t claim this any longer.

    You get frustrated when people claim they just KNOW humans are 100% the cause of climate change. In fact when people say they “just know”something is true, it frustrates me immensely as well. However I don’t think climate scientists and warmists are really saying that. I think you mistake a certain level of passion and knowledge for over confidence and hubris. There’s a difference between knowing, and being certain or 95% sure, and sure that alternative theories have huge flaws in them.

    The agw consensus is strong imho because so many different lines of evidence point in that direction of agw.

    Regarding your view that agw is largely about left wing tribalism. If a preponderance of left wing people agree we are warming the climate, maybe they are simply correct on the issue. But I don’t believe they agree on the issue to push some agenda, or be in some tribe, its more that for some reason left wingers are more accepting of science in general, although not unthinkingly so.

    However please note that Pew Research shows while liberals do accept the science more than conservatives its something like a 60 / 40 split, so not as hugely tribal as you are making out. This is important to appreciate.

    I used to be sceptical of agw, and it was only looking carefully at claims by both sides of the debate that I realised agw was the more rational and stronger case. I’m not claiming absolutely everything about agw is 100% settled science, but to me the important basics are and humans are the dominant cause.

    It’s nothing to do with tribalism for me, and while I have my political leanings, I think such political tribalism should be minimised.

    So much of the ‘denialist’ side of the science is nothing more than cherrypicking and sometimes complete lies. There’s really nothing of substance there when you strip away all the crank science, bluster and rhetoric.

  10. 60
    Dan says:

    re: 52. Wow,you reference Lindzen as if that has some validity over the vast peer-reviewed research to the contrary. Talk about classic cherry-picking. Read and learn:

  11. 61
    nigelj says:

    Dan De Silva @51

    There is simply no comparison between the saturated fats issue and climate change. There may be some truth to the claim that the sugar companies carried out or funded anti fat research , but Greenpeace doesn’t really carry out climate science research or fund it, certainly not in any quantity.

    Climate research is mostly funded by governments and universities and anonymous donors specifically as this removes as many industry and lobby group vested interests as possible.

    This is all an ideal example of your irrational thinking and conflating things looking for some political angle.

    I have some respect for Greenpeace, but they go over the top sometimes.

    It may however be true that scientists tend to be at least moderate environmentalists. Any ideas why? (Sarcasm)

    And the left as a whole don’t demonise corporations in principle ( a few extreme cranks might) . The left say that sometimes corporations behave badly, and business should be regulated. I would agree with that position. Are you claiming they never behave badly or should be free of regulation? Again your line of thinking is irrational if you do.

  12. 62

    “Human nature cannot be fully corrected by peer review, but overwhelming evidence will change minds.”

    Dan, many years ago, I lent the very jet lagged fiance of a friend’s brother a guestroom after she flew in from Japan via Europe en ruote to join him at Stanford. She took the house to dinner en route to the airport thr next day, and there I asked her why , though a sucessful abstract painter, she was entering business school ?

    She replied: ” I study business because I am Zen Bhuddist and want to achieve empty mind. ”
    Seeing her anaswer perplexed us , she continued:

    “Much money, empty mind.”

    It is hard to imagine a sum large enough to place Marc Morano, David Suzuki , Scott Pruitt or Naomi Klein in that mental state.

  13. 63
    MA Rodger says:

    Dan DaSilva @58.
    The “experience” you relate concerned what was perhaps your second comment posted @RealClimate and occured years after your first. What you describe as being a question from one of our hosts was a rhetorical question and thus not an enquiry asking for a reply. The message to you was “That’s the stuff of denialist lore, not legitimate science. But thanks for stopping by :-)” Thus your boreholed reply (which wasn’t much of a reply for a science website and certainly didn’t address the topic) shouldn’t be such a great surprise.
    Denialists like yourself do get a level of tolerance here, in my own view far more than you deserve. The pet denialists we gain from such tolerance vary greatly in their stance on AGW and their attitude to RealClimate but do share an inability to take on-board any evidence that they find contrary to their own aberrant views on AGW. As you seem to be taking up residence, perhaps it is time to identify what it is constitutes your particular flavour of denialism. That would allow the ridicule to be properly directed.

  14. 64

    DDS, #52–

    Here is an idea for all the climate scientists out there. Run your models with a lower sensitivity.

    Unfortunately for this suggestion, most models don’t have a specified sensitivity that can be adjusted. It’s an emergent property in all fully coupled models, I believe. (Some simpler models–some of the ones falling under the classification EMICS, “Earth Models of Intermediate Complexty”, I think–do have a specified sensitivity–handy where sensitivity is usefully treated as an independent variable.)

  15. 65
    jgnfld says:

    “In my opinion “climate science” is highly invested in politics.”

    Your opinion is worthless without facts and evidence. And no, there is no evidence of any worldwide conspiracy among politicized scientists to lie about the greenhouse effect.

    “I was just wondering what the opinion would be of turning all important decisions which involved some technical judgment over to a panel of the SCIENTISTS with a PEER REVIEW? I think this is a very bad and awfully terrible idea but the readers of RealClimate may have other opinions.”

    You are talking about nonscientific decision making. Apples and oranges reasoning doesn’t get one very far with reality.

  16. 66
    Night-Gaunt49 says:

    I don’t believe in Anthropogenic Global Warming (AGW) anymore than I believe in the theory of Evolution. Both have been proven over and over again to be a fact. Now in both cases some of the elements of it are unknown or not yet nailed down, but the over all theory is sound and proven again and again from a variety of sources and literally thousands of different scientists in many different fields. However the wedge of doubt has been wielded successfully by Koch created and funded entities to put in the layman increase doubt. (See how it was used against those showing proof of cancer related causes from cigarette smoke and Evolution by these same techniques. Now that is dangerous for all of us. The Fossil Fuel Corporations seem dead set on burning up the the remaining carbon in the ground even though they know it will be catastrophic when they are done. They have no problem to cast down on the entire scientific method to win. And since the average American is as ignorant in the rudiments of science as they are in geography and global politics, it is no wonder the lies are winning.

    What has been done will be a boon to stopping and changing the lies winning to the lies losing with it as an education aid. We just need and interested billionaire to spread it far in wide to every school ever politician.

  17. 67
    Ray Ladbury says:

    Some are denialists. Some are contrarians. Some are narcissists who prefer the acclaim of the denialosphere to obscurity in the trenches of science.

    None are productive.

    DDS@53–that is not a quote from me, but rather from Nigel.

    DDS: “Run your models with a lower sensitivity.” Sorry, dude, that isn’t how climate models work. There isn’t a dial for “sensitivity”. These are physical models–and Richard Lindzen gave up being a scientist a long time ago.

    DDS: “In the case of “global warming” skew is caused by the environmentalist mindset. (Greenpeace comes to mind).”

    Uh, dude, how many climate scientists do you suppose are members of Greenpeace? EDF? Dude, this is just stupid. James Hansen if a fricking Republican. When you say things like this, you reveal yourself to be a complete, utter, drooling moron. Turn off Faux News and read an actual news source.

  18. 68
    Hank Roberts says:

    MA Rodger says:
    28 Apr 2018 at 6:42 PM

    Dan DaSilva @58.
    The “experience” you relate …

    Thanks for tracking that down. I hope refreshing his memory about what he said helps him judge his comprehension.

  19. 69
    Mal Adapted says:


    However, after that experience, RealClimate has been very fair and I only got tossed in the hole a few times for things that may have deserved it. So as not to abuse that privilege I will refrain from any more comments on this thread. Thanks for the interaction.

    That was gracefully said. If Dan can acknowledge that some of his comments were worthy of being boreholed, maybe he can ask himself honestly just why he’s so ‘wary’ of climate scientists. If he can track down his (pre|sub|un)-conscious cognitive motivations for his oddly particular mistrust, he may eventually get past it.

    Dan, although you’re suspicious of the motives of climate scientists, you appear to acknowledge your own lack of expertise, and to recognize genuine expertise in, for example, the principal authors of this blog. OTOH, when you don’t understand how a particular scientific conclusion is reached, you display a marked propensity to assume nefarious intent on the scientists’ part; and to draw alternate conclusions that appeal to you more, at least judging by your dogged adherence to some of them.

    One conclusion you’ve long since reached is that climate scientists as a class are biased toward the ‘left’ end of your single-axis political model. When did you reach that conclusion? What evidence do you think supports it? If you argue here on the basis of climate ‘science’ you obtained from non-peer-reviewed sources, why do you trust those sources more than you trust peer-reviewed ones?

    If, however, you don’t trust Judith Curry, Richard Lindzen or Alex Jones any more than you trust Gavin Schmidt, you may think you can puzzle out ‘the truth’ all by yourself. The problem, painfully clear to the rest of us, is that you really aren’t competent to distinguish between specious motivated sophistry and rigorous evidence-based argument, and you won’t be until you put the time and effort in to be the peer of full-time climate specialists. A genuinely humble skeptic has internalized these uncomfortable truths before reaching adulthood!

    Earth’s climate is a complex natural system, and scientific inferences about it must be based on all available evidence. Comprehensive literacy in the evidence bearing on AGW demands prolonged, focused attention. Furthermore, salient evidence converges from multiple independent lines of research, conducted over two centuries in the US and around the world. You must therefore have a sufficiently broad scientific foundation to recognize consilience. For example, before proposing that the expert consensus for AGW is politically biased, shouldn’t you in all humility trace the political biases of Joseph Fourier, John Tyndall, Svante Arrhenius and so forth through the present, and show us where a ‘liberal’ bias crept in? Another example would be to explain why Arrhenius, who as a Swede was reportedly in favor of a little warming, obtained ECS results from his simple, laboriously hand-calculated model of CO2-driven global warming that are only a factor of two higher than estimates by the current ensemble of coupled GCMs.

    Lastly you have to be humble, and open to the finite probability that your trained and disciplined specialist peers can see mistakes in your argument that you can’t. You can depend on your peers not to let you get away with fooling yourself. Without them, you have no way to know whether or not you’re fooling yourself!

    OR: my assumption of Dan’s good faith were overly optimistic, and he in fact wishes to remain erroneous. He’ll either respond defensively to my comment or, more likely, ignore it. Meh.

  20. 70

    DDS 45: Is MIT Professor Richard Lindzen a denier?

    BPL: Yes. He has “emeritus disease.” He formed a perfectly reasonable theory, published in a paper in 1982, that global warming would be mitigated by a “tropical infrared iris.” Satellite observations shot him down.

    At this point, a good scientist would have changed his opinion, since the data didn’t support the hypothesis. But that’s not what Lindzen did. He republished essentially the same paper in 1992, and again in 2002. He can’t stand the fact that his pet theory was simply wrong, and he has become the Halton Arp of climate science.

    It doesn’t help matters that he boasts about the oil money he receives for his crackpot lectures.

  21. 71

    DDS 51: Otherwise, you could answer all questions by just having scientists vote.

    BPL: And he still doesn’t get it. After all the attempts people here have made to define what “scientific consensus” means, Dan still maintains that it’s a bunch of scientists voting on what they believe.

    Time to give up on this guy. I’ve never seen a worse case of “I don’t want to hear what’s true because I already know.”

  22. 72
    Vendicar Decarian says:

    RE 51 – “Human nature cannot be fully corrected by peer review, but overwhelming evidence will change minds.”

    Flat Earth conspiracy theorists gather to discuss ‘proof’ at first UK convention

  23. 73
    Vendicar Decarian says:

    Re 52 – “You might become a target of your peers by assuming a lower sensitivity”

    What would be the point of attempting to placate those who can not be placated by assuming what they want to be assumed rather than by using best estimates, rather than dishonest assumptions?

  24. 74
    Vendicar Decarian says:

    Re 53 – ” Or possibly they do not think it worth their time, I do not know.”

    Denialists are a dime a dozen, and all are willfully ignorant of science.

    Best just to steam roll over them and relegate them to the same category of willful ignorance as the Flat Earthers, and Evolution Denialist Kooks.

  25. 75
    Vendicar Decarian says:

    Re 51 – “If you want to find the evil look to people trying to create a utopia.”

    Stupid people say stupid things all the time. And that is about as stupid a statement as I have ever seen.

  26. 76
    Vendicar Decarian says:

    Re 36 – “In my opinion “climate science” is highly invested in politics.”

    You are the only person talking about politics here.

    Politics is of course one method used by denialists to deny science and that is why
    denialists need to be steam rolled and relegated to the dustbin of history.

  27. 77
    Dan DaSilva says:

    My out of body self-recursive thoughts:
    Why are we exerting so much time and effort on this guy? He has written nothing of substance and yet otherwise productive individuals are sitting at their computers wasting their time. Are we trying to convince him or ourselves? I can understand if he was making at least semi-valid points that needed to be refuted but what have you read that deserves this level of effort?

  28. 78
    Mac says:

    Re #54, DDS:

    Do I still get the denier label? (Not that I care I was wondering if you are consistent)

    I’m not interested in taking a full inventory of your beliefs, nor particularly enthralled with the value of sweeping labels. Regardless, it’s not about you, anyway. I’ll offer brief counterarguments when I think someone is uttering something foolish with authority, and once in a while I even learn something myself.

    And consistency is nice, but calling someone inconsistent is one of the most frequent ad hominems you ever see see in stupid online arguments, which does nothing to address the reality basis of one’s scientific understanding. So nice try, but whether I’m consistent or not has nothing to do with the fact that your perspective on the AGW science appears deeply and deliberately flawed. So I’ll let Ralph Waldo Emerson offer my final words here: “A foolish consistency is the hobgoblin of little minds.”

  29. 79
    MA Rodger says:

    Looking back through Dan DaSilva’s comment history, he was first active at RC as a simple troll, as in this a singleton comment lobbed into a comment thread from last year (on the subject of extreme weather under AGW, although that isn’t probably relevant):-

    “The model is indeed simple, ridiculously so. Oh but wait it is “calibrated”. Another word for fudging your model to meet past results. This my friends is not science it is mental masturbation.”

    Unusually, Dan DaSilva is a troll who considers he had enough of a grasp on climatology to treat the authors of the science as though they were as inexpert as Wattsupia’s finest, this from the beginning of the year and directed at one of our hosts (on the subject of ECS estimation):-

    “The claim of reduced uncertainty for equilibrium climate sensitivity is premature” This is what many climate skeptics have been saying for years and they have been called deniers for their efforts.
    How does it feel to be a denier? Probably feels like you are doing science and you do not care what other less informed may say. Welcome to the camp of “the deniers”, those for who the science is not settled.

    Yet over the last few weeks Dan DaSilva has been replying to comment he generated. (He justified a previous stint at replying here by saying “Why Am I here? One factor is that I have not yet been sent to the borehole.”) These proper interchanges do give more indication of the Da DaSilva version of AGW truth that may be worth a further comment. Even though Dan DaSilva tells us @58 that he will “refrain from any more comments on this thread,” we have not seen the last of him (as his trolling comment @77 plainly demonstrates.

  30. 80
    Mal Adapted says:


    My out of body self-recursive thoughts:
    Why are we exerting so much time and effort on this guy? He has written nothing of substance and yet otherwise productive individuals are sitting at their computers wasting their time. Are we trying to convince him or ourselves? I can understand if he was making at least semi-valid points that needed to be refuted but what have you read that deserves this level of effort?

    Uh – which guy, Dan? What does ‘self-recursive’ mean here? Is it possible you are referring to yourself?

  31. 81
    Hank Roberts says:

    For DDS, who asked

    Why are we exerting so much time and effort on this guy?

    You can look this stuff up.

  32. 82
    nigelj says:

    Dan de silva @77

    “Why are we exerting so much time and effort on this guy? He has written nothing of substance and yet otherwise productive individuals are sitting at their computers wasting their time. Are we trying to convince him or ourselves?”

    Neither. I don’t need to convince myself, and I know you are never going to be convinced. Dont flatter yourself. I rebut your sort of nonsensical commentary in case the virus spreads to fence sitters reading websites, and for the mental exercise and because I like discussion on serious topics, and I’m semi retired. I read this website mostly to learn something from the experts.

    You are a conspiracy theorist, obsessed with politics which you believe infests every decision. You take a small potential issue, and blow it out of proportion and distort it, so typical of conspiracy theorists.

    You are smart enough so should be able to recognise your own dysfunctional leanings towards conspiracy ideation, so I think you are being intellectually lazy and unable to accept you are sometimes wrong, a common human failing. Then again, maybe Ray Ladburys harsher and amusing assessment at 67 is nearer the truth.

    And another thing on “peer review”, You hold up this to be the arbiter of the truth, when it is merely intended to sort good science papers from bad papers, to sort the wheat form the chaff, like revewing a pile of job applications. It is not likely to identify the one perfect science paper, because the review panels are too small, and and brilliant research papers are those that slowly gain wider support in the science community. Peer review is better seen as just one part of quite a good process. But alas, I suspect you wont be prepared to see it this way, even although its rather obvious.

  33. 83
    JB says:

    Not one slide on climate sensitivity except the initial 1.5-4.5 range that has still not been narrowed despite 40 years of research and technological progress.

    This is the only number that matters. If climate sensitivity is low (and the evidence is increasingly supporting that conclusion), we have very little to worry about. What does it tell you about a field that is unwilling or unable to narrow the error bars on the key quantity driving policy decisions in over 4 decades of extremely well-funded research?

  34. 84
    nigelj says:

    JB @83

    “This is the only number that matters. If climate sensitivity is low (and the evidence is increasingly supporting that conclusion), we have very little to worry about. What does it tell you about a field that is unwilling or unable to narrow the error bars on the key quantity driving policy decisions in over 4 decades of extremely well-funded research”

    Wrong. The evidence overall remains the same, that the most likely number for climate sensitivity is at least in the middle of the range. Although it should be noted that climate models that are most accurate are consistent with high sensitivity.

    Even low climate senstivity is very concerning, because assuming purely for the sake of argument that it turned out to be low, sea level rise over the last decade or so has been towards the UPPER end of predictions. And we have evidence of ice sheet destabilisation in Antarctica. So there will be no comfort even if it was low sensitivity.

    The reason its hard to narrow down climate sensitivity is we can’t shrink the planet and put it in the laboratory. It took decades to find the higgs boson as well despite huge efforts. Your comments are just stupid.

  35. 85
    MA Rodger says:

    JB @83,
    You tell us “If climate sensitivity is low (and the evidence is increasingly supporting that conclusion), we have very little to worry about.”
    I hate to worry you about it, but where is this evidence which you say “is increasingly supporting that conclusion?”

  36. 86
    Ray Ladbury says:

    What it tells me is that you don’t understand climate policy or research. Even with the limited warming we have had so far, we have already committed ourselves to several feet of sea level rise. We are acidifying the oceans, killing coral reefs, etc.

    I also wonder how you morons in the denialist camp got the idea that climate sensitivity is some sort of simple parameter one dials into the models. It is not. It is an emergent quantity that only emerges when you get ALL the details of the model right. You literally have to understand just about everything about climate before climate sensitivity converges.

    Third, climate science has made tremendous strides on a very difficult system in a relatively short time. The fact that you are too dim to understand this progress does not in any way diminish it. Now, run along. The adults are trying to have a discussion.

  37. 87

    If climate sensitivity is low (and the evidence is increasingly supporting that conclusion), we have very little to worry about.

    No. Temperature rise, remember, is the product of emissions times sensitivity, essentially. So if the emissions are sufficiently large, even low ECS values could get us to very bad places. That the carbon exists within Earth systems to do so is clearly evidenced by geological history.

    However, a ‘back of the envelope’ calculation shows the same thing for our current geological reality.

    “…in total there are four to five times more fossil fuels in existing reserves than can be safely burned.”

    (First random search result!)

    More specifically, there is something like 3200 Gt of carbon in those existing reserves. So, ignoring the fact that there is certainly still more fossil fuel to be found, ’emittable’ CO2 is: 3.66 x 3200 = 11,712 Gt CO2.

    If we accept the highly risky assumption that extant carbon sinks will continue to be effective over the entire range of that CO2 ‘slug’, then we could say that approximately half, 5856 Gt, will end up in the atmosphere. That’s pretty close to two doublings of current CO2.

    The Curry & Lewis paper which is the current lukewarmer ‘darling’ estimates ECS at ~1.6 C, hence giving a mean global temperature increase ~3 C–and not over pre-Industrial, either; that would be over present temps, which are already elevated by about 1 C.

    That, in turn, would place us firmly in the Mark Lynas’s “Four degree world,” which I think we can be assured is not a place we want to be. For one thing, we’d see an ice-free Arctic Ocean–probably perennially so, eventually, which would be highly disruptive to global circulation–and for another, a highly significant deglaciation of Antarctica with consequent SLR of up to 20 meters:

  38. 88
    Hank Roberts says:

    JB contradicts himself, saying

    If climate sensitivity is low (and the evidence is …

    and then noting that no evidence has constrained the earlier estimates of the range of uncertainty.

    Premature conclusion we have no worries, mate.

  39. 89
  40. 90
  41. 91
    Dan DaSilva says:

    83 JB
    Good point, the fact that the sensitivity range has not narrowed is an indication that there is a large amount of tension between climate scientists. (A similar dynamic can be seen in the trading markets, in that case, the extended trading range tightens as bulls and bears fight until there is a breakout.)

    When this deadlock breaks we will be witnessing the next great step in the evolution of the debate. If Judith Curry’s (and similarly orientated scientists) analysis is accepted it will further dampen the argument for alarm. My somewhat pathetic layman’s review of her work indicates she and similar are making an undeniable (pun not intended) case and will win.

    PS: I would like to apologize for breaking my promise to refrain from comment on this thread (although I have toned down). This wonderful site, great comments, and expert insight are too much to resists.

  42. 92
    Dan DaSilva says:

    The performance of models using a climate sensitivity range of from 1.0 to 5.0 is essentially equal in hindcasting. How is that possible?

  43. 93
    Daniel DaSilva says:

    83 JB
    You just put into two paragraphs essence of the problem, which I could not.

    Also, I have been critical of climate models because of hind-casting. I pointed out that it was “possible to curve fit” when use hind-casting. Not that I believed that was what was happening, only that it was a danger. Know I believe this is indeed happening,

    Your paragraphs indicate why climate models have so many problems; the most important response is completely unknown. Each climate model has its own equilibrium climate sensitivity. So how do all the models achieve a response that looks somewhat like the real world response? Through the tuning of other uncertain quantities.

    This is a problem which can not be solved at this time. These uncertain quantities consists of many things including response to aerosols, water vapor/clouds and the time constant of ocean heat storage that have no solution at present.

  44. 94
    David B. Benson says:

    JB @ #83 — Maintaining current levels of CO2 will return the climate to that of the mid-Pliocene. The sea stand was about 25 meters higher then. See the Wikipedia page on Pliocene climate.

  45. 95
    Hank Roberts says:

    … an indication that there is a large amount of tension between climate scientists.

    Uh, no. Each time the climate has had an excursion, it’s been a different climate.
    Different continental positions. Different plankton populations living at different places in the ocean. Different icecaps. Different biosphere.

    You want to make a market comparison? This is more like the way capitalism has survived every major market crash. But it’s a different capitalism after each recovery.

    If you could run the economy a hundred times through, you’d get varying results on each run because each of the variables can, well, vary.

  46. 96
    Dan DaSilva says:

    86 Ray Ladbury,

    Hello Ray,
    We get it, and the earth has no dial to change climate sensitivity either. I assume the programmer of a model can adjust parameters and/or code which then will at some point will produce an output which can be interpreted as adjusted climate sensitivity.

    You seem to believe that these models are reproducing the functions of the earth in some pure and cosmic way which is uncorrupted by human hands. Well, I have written and seen more computer code than I would care to recall and I tell you that large computer programs written by the best software professionals have bugs and are very hard to verify or comprehend.

    What do you think emerges when you do not get ALL the details right?

    Did JB hit a nerve or are you having a bad day?

    Thanks, Dan

  47. 97
    jgnfld says:


    How many times must you be corrected in your misstatement that the climate models we are talking about (GCM models) “use” predefined ECS values as an input parameter in the first place? They do not. You are confused, or lying, or both.

    Why do you persist in repeating and re-repeating an easily verified falsehood? Is it stupidity, ignorance, or malevolence?

  48. 98
    Dan DaSilva says:

    94 David B. Benson
    Is that a consensus opinion or just you own best estimate?
    Thanks Dan

    87 Kevin McKinney
    I am willing to concede on every point except one; Climate Science does not know what the climate sensitivity is. Can you at least give me that? I have a Tesla in the family by the way.

    Thanks Dan

  49. 99

    #92, DDS asks:

    The performance of models using a climate sensitivity range of from 1.0 to 5.0 is essentially equal in hindcasting. How is that possible?

    Dan, I’d be interested to know more about the sources for, and context of, that statement–who says, why, and in what circumstances?

    I’m particularly interested in the last, because it occurs to me that if you are talking about historical periods during the great bulk of the Holocene, when GHG concentrations have been exceptionally stable by the standards of geological history in general, then you wouldn’t expect the climate sensitivity to be a dominant factor in driving climate. Other factors would predominate.

    But I’m quite skeptical of the statement in general, because I know there is quite a bit of model spread, and it seems unlikely that that model spread is completely independent of ECS. For example, I’d draw your attention to Figure 9.7, p. 766, of Chapter 9 of AR5, which shows significant differences in model performance, albeit not assessed in relation to climate sensitivity. One can also see a lot of variation in the model spread as illustrated by the ‘spaghetti plot’ of GMST trajectories in Figure 9.8 (p. 798).

    I’d also note this bit, from much later in the chapter (p. 825):

    In some cases, the spread in climate projections can be reduced by weighting of models according to their ability to reproduce past observed climate. Several studies have explored the use of unequally weighted means, with the weights based on the models’ performance in simulating past variations in climate, typically using some performance metric or collection of metrics…

    None of which sounds very supportive of the notion that model performance is ‘essentially equal’–though admittedly the correlation with TCS is not examined directly.

    Moving on, many of the following quotes are relevant to various iterations of CMIP, which is an ongoing effort to coordinate modeling activities by creating some standards (both in terms of input data and experimental setups). More about that here:

    Suggestive of support for Dan’s perception is this (p. 820):

    Despite the range in equilibrium sensitivity of 2.1°C to 4.4°C for CMIP3 models, they reproduce the global surface air temperature anomaly of 0.76°C over 1850–2005 to within 25% relative error. The relatively small range of historical climate response suggests that there is another mechanism, for example a compensating non-GHG forcing, present in the historical simulations that counteracts the relatively large range in sensitivity obtained from idealized experiments forced only by increasing CO2.

    Seems clear enough, if a tad vague: differences in forcings tend to compensate for differences in sensitivity. Is that because of model tuning, as Dan suggests? Maybe; the goal of modeling, after all, is to create as accurate a simulation as possible.

    A few sentences further on, though, we find:

    However, despite the same range of ECS in the CMIP5 models as in the CMIP3 models, there is no significant relationship across the CMIP5 ensemble between ECS and the 20th-century ERF applied to each individual model (Forster et al., 2013). This indicates a lesser role of compensating ERF trends from GHGs and aerosols in CMIP5 historical simulations than in CMIP3.

    So that appears not to be the case for CMIP5. Frustratingly, it’s not clear whether the variation in tracking 20th-to-early-21st temperature trends is greater for CMIP5 than 3, so while the ERFs do not show the same relationship, the other side of the question here is left unilluminated by the text.

    But we’ve been skipping over what ECS actualy is in CMIP3 vs. CMIP5 (p. 817):

    The method of diagnosing climate sensitivity in CMIP5 differs fundamentally from the method employed in CMIP3 and assessed in the AR4 (Randall et al., 2007). In CMIP3, an AGCM was coupled to a non-dynamic mixed-layer (slab) ocean model with prescribed ocean heat transport convergence. CO2 concentration was then instantaneously doubled, and the model was integrated to a new equilibrium with unchanged implied ocean heat transport…

    In CMIP5, climate sensitivity is diagnosed directly from the AOGCMs following the approach of Gregory et al. (2004). In this case the CO2 concentration is instantaneously quadrupled and kept constant for 150 years of simulation, and both equilibrium climate sensitivity and RF are diagnosed from a linear fit of perturbations in global mean surface temperature to the instantaneous radiative imbalance at the TOA.

    So, for CMIP5, the diagnosis of ECS involves a much larger change in forcing than the period of observation (ie., ~40% increase in the ‘real world’, vs. a 400% increase in the diagnostic test of model sensitivity.) If the period of observation, and the magnitude of the real world forcing, are insufficient to diagnose ECS with good precision, should we be surprised that models with different ECS may not be strongly differentiated in terms of performance over that period?

    All of which is less conclusive than anyone would like. But partly that’s because the context needs to be better defined.

    So, Dan–whose opinion are you relying on, based on what information, and relevant to what context, exactly?

  50. 100
    nigelj says:

    DDS @93, you persist in this mistaken belief that climate models are curved fits despite all the experts here telling you they aren’t. You provide no specific evidence from a model. Its at the point where you are spreading nonsense or plain lies without any solid, specific evidence to back your claims, and I wonder why this website tolerates that. Scepticism is ok by me, but has to be backed up by science.

    Models don’t all get the same results, look at model data comparisons on this website. They all use slightly different approaches to the problem, different equations and elements included even down to the complex models include the transpiration of plants in some cases. I get this, and I’m more or less a lay person.

    I think you obsess over hind casting. Models will obviously be adjusted until they hind cast well, that is the whole point. Equations are developed or modified in any scientific field until they make accurate predictions. They don’t come on gold tablets from God.

    Imho its more instructive to look forwards to predictions of the future. Even Hansens old 1988 models predicted warming over the next three decades passably ok and obviously couldn’t have been tweaked to do this. This form of prediction of the future is more important and excellent validation of a model.