Monday, May 10, 2010

The Hockey Stick Illusion (A.W. Montford)

The subtitle for this excellent book is 'Climategate and the corruption of science' which sums up the sad tale. Montford succeeds in making a technical statistical argument quite readable, which is surely a sign of divine assistance.

In brief, and cutting out much fascinating detail, the story is this:
- until the mid-1990's the consensus on climate history was that there was a 'Medieval Warm Period' (with temperatures higher than today), followed by a 'Little Ice Age', and then, from about 1850, a rise in temperature through to today;
- in the late 1990's a group led by Michael Mann devised a new history in which those highs and lows were flattened out, and the rise in temperature in the twentieth century was emphasised - this is the 'hockey stick';
- the scientific rationale for the hockey stick was progressively investigated, especially by Steven McIntyre, and has been comprehensively demolished;
- the scientific credibility of the IPCC in this regard is less than zero;
- the 'hockey team' - ie those around Mann and supporting his work - resorted to a great many dirty tricks and obfuscations to confuse this truth. "Climategate" was simply the airing of the dirty laundry (almost certainly a leak from somebody inside who was disgusted by the attempt at covering up the truth).

The funny thing is that the hockey stick as such is pretty marginal to the question of whether AGW is true or not. It can, however, serve as something of a litmus test - anyone who accepts it reveals that they are ill-informed. For me, this is the most significant chart re AGW:

Even if we do nothing (and we won't, so this is worst case) the CO2 concentration is likely to peak at around 450ppm, roughly equal to a .7C rise in temperature.


  1. Sam, I assume you have read the detailed NAS report on the hockey stick graph. How does Montford (NB not Mountford) account for the fact that this report from the most respected scientific body in the US broadly vindicated Mann et. al.? Here's a quote from the report.

    “The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on ice caps and the retreat of glaciers around the world, which in many cases appear to be unprecedented during at least the last 2,000 years.”

    What is the source for your final graph? I assume it is here. Does he include non-conventional fossil fuels? How idiosyncratic is his analysis? (i.e. is it accepted by other experts?) I notice that it also doesn't include either non-fossil fuel emissions nor feedback mechanisms, so that even if fossil fuel contributions could only get us to 450 ppm, the ultimate stabilisation level is still likely to be considerably higher.

    (almost certainly a leak from somebody inside who was disgusted by the attempt at covering up the truth).

  2. Amended his name, thanks.

    Montford spends quite some time on the NAS report, which he presents as a political stitch up which didn't go into the contended issues. I found his presentation plausible. (The Wegman report gives a different flavour, and does look at the statistical side).

    Yes, the final graph comes from Rutledge.
    Non-conventional fossil fuels (tar sands?) are marginal, especially in EROEI terms, so I don't see them as significant. I've become a bit more suspicious about the feedback mechanisms since understanding more about the hockey stick - if we survived higher temperatures in the MWP without boiling the oceans, we'll probably survive this one too :o)
    Other factors - eg deforestation - are bad on their own terms.

    (I know, I'm a heretic)

  3. The Wegman report appears to be a terrible piece of scholarship. I haven't had time to look at it in detail, but below are a series of posts apparently documenting its blatant plagiarism of significant sections of both background discussion and substantive "work", occasionally making changes that actually obscure the point under discussion.


    And more here

    For some of the background, see also here and here.

    That said, even if Mann et al. 1998 needed to be retracted, its basic conclusion has been corroborated by numerous other studies since then using very different methodologies.

    But as you say, paleoclimate reconstructions are actually not a critical part of climate change theory. So even if all reconstructions were dropped, there would still be a huge body of evidence and theory pointing to a very alarming situation. Arguments about a single paper from twelve years ago are fairly marginal to the main game, so let's turn again to the more important issue you raise at the end of your post.

    I've become a bit more suspicious about the feedback mechanisms since understanding more about the hockey stick - if we survived higher temperatures in the MWP without boiling the oceans, we'll probably survive this one too :o)
    You realise that there is a time lag between GHG levels and temps such that today's temps do not yet reflect current GHG levels? Therefore, even if global temps were similar to today 1,000 years ago (and this is unlikely), CO2e levels were much lower back then. So if/when we get to 450 ppm, we have locked in enough warming to take us multiple degrees above any reconstructed historical temperature and well into possible feedbacks that would be novel within human history.

    Regarding EROEI for unconventionals (which is not just tar sands also shale oil and a few other things), despite their lower EROEI they are nonetheless currently being exploited. There might not be as much profit in them as conventional production, but their huge volumes means that they have to be included in any calculation of total potential recoverable fossil fuels and hence possible CO2 emissions. Of course there is still the complex questions of calculating the total resource and estimating what proportion is likely to be exploited and burned. Nonetheless, this will be a non-trivial amount.

    Remember that CO2e also includes methane and nitrous oxide from agricultural activities, as well as deforestation and changes in land use and so on. So getting above 450 ppm is not an issue, even if it is true that the IPCC have overestimated potential fossil fuel based emissions.

    Furthermore, CO2 levels have a twin problem along with climate change, namely ocean acidification, which provides further reason to be deeply concerned about carbon levels even without climate considerations.

  4. Sam, I'm not concerned about you being a heretic (apart from on virgin birth, but that is a discussion for another day, and while it might earn you a minor heterodoxy label, doesn't equate with heresy). I'm concerned that you might be sticking your head into the sand for ideological reasons that have little to do with the science. I keep pushing back on this because you are an excellent communicator and one of a relatively small number of Christians thinking theologically and pastorally about these matters. I know that at one level, reducing oil dependence (and our profligacy with energy generally) can be motivated either by considerations of peak oil or of climate change, so either can be a sufficient basis for getting the ball rolling (and of course, considerations of idolatry, greed, hubris, gluttony and so on are also crucial elements to throw into the mix, along with the love for neighbour that give PO and CC some of their ethical traction). Nonetheless, there are sufficient differences between the responses required (the merits of developing unconventionals being one notable example) to justify my wanting to achieve some kind of agreement with you on this (amongst other reasons). Perhaps it is not going to happen, but I don't want to give up prematurely.

    Grace & peace,

  5. Byron - I suspect that if we ever had the chance to share some beers then solid agreement would be swiftly forthcoming :) My disagreements about AGW are academic in both senses of the word (ie descriptive and pejorative) and, with a handful of minor quibbles, I don't think there'd be much disagreement on what steps actually need to be taken, eg things like carbon taxes, reduction of private transport, massive emphasis on renewables, relocalisation and so on.

    I'll have a read of your links re Wegman etc.

  6. Oh dear, just started reading one of those deepclimate articles. I feel a fisking coming on...

  7. Byron - I've now had a read of those articles (skimming some bits) and I'm just wondering _how_ we might have a further dialogue on this. I'd be happy to pursue the topic, not least because a) I have a great deal of respect for where you're coming from, and b) I think our overall perspectives are close enough for the conversation to be productive. But those deepclimate articles are... well... I don't think they achieve what they set out to achieve.

    I suspect we'd need to set out the parameters first, eg agree on what we think counts as 'good science' (or 'good argument') before getting stuck into the specifics.

  8. Sam, I still think you're very courageous (in the 'Yes, Minister' sense) to get involved in the climate change disagreement. Even with a background in mathematics and statistical analysis of oil markets I wouldn't for a second presume to imagine I could judge between the competing scientific professionals working on climate change - and so I'm very dubious about any scientific layman who thinks they can, however much I like them :).

    Mind you as I've said to you before, I'm also dubious about professional scientists in other fields who tribally support their earth sciences colleagues just because they're all sick of pseudo-science and the general public's inability to tell the difference.

    There is too much blind trust among scientists of each other's intellectual rigour, and too much ignorant mistrust among lay people. I'll just be glad when our energy profligacy is forced to an end.

  9. Tess, I agree that non-experts looking into a field can frequently offer criticisms that seem cogent to them, but to those with more familiarity in the field are obviously barking up the wrong tree (to coin a phrase...). My own experience of some areas that I know a little about makes me aware of this phenomena. For example, Sam's series on humourless atheism provided many examples of non-theologians making elementary mistakes in their attempt to write off the entire endeavour. Sam's patience with some of his interlocutors was highly commendable.

    So while it is possible that sometimes an emperor needs to hear that he has no clothes from a child, in general, credentials matter. I would not presume to be able to judge between competing scientific professionals working on climate change. Instead, I will have a strong bias towards those who are actively publishing in recognised peer-review journals and whose work is accepted by reputable national and international scientific bodies. And while there are certainly live debates

    Sam, I hadn't had a chance to do more than a very brief skim of the Deep Climate pieces when I posted those links. My apologies. In my estimate, having now looked at them again, they are relevant, but not crucial, to an evaluation of Wegman. A summary of my understanding: in some background discussion, Wegman used unattributed material lifted almost verbatim from one of the scientists he was investigating (Bradley). The changes that were made shift Bradley's meaning in ways that disagree with and undermine his work without the source of these changes being specified. Is that a fair summary? I could have got it wrong.

    More relevant seem to be this and this and this. Obviously, two of these posts are by Mann himself, but his defence is clearly important to any evaluation of criticism against him. Do any of these posts address issues raised in the book?

    Sam, I'd love to have a beer. I've been intending to see whether I can swing out to Mersea sometime if I'm heading down south. Please do let me know if you're anywhere near Edinburgh. Are you considering the Dark Mountain festival in Wales?

    PS I'm just wondering _how_ we might have a further dialogue on this
    I wasn't quite sure how to read this. Was it an expression of dismay at how far apart we obviously are based on my linking to DC? Was it intending to raise the question of the parameters and assumptions in a conversation? Or was it something else?

  10. Oops - unfinished sentence at the end of para #2. You can probably guess where I was going. Something like "While there are live debates amongst climatologists, they are not necessarily the same debates that are happening on blogs or talk shows".

  11. Byron - on your last PS it was the second, ie about setting up the parameters of the discussion. I'm going to stick up a blogpost about it, now that my brain has (mostly) returned from lurgi-land.

  12. Thanks for the link. I haven't followed the whole thread or discussion (I remember reading bits of it back in 2008), so I might have missed the point. I assume you've posted it because it gives an example of you defending a (limited) use of expertise and of multiple lines of attesting evidence where the loss of one doesn't destroy the whole case? I.e. to show that we have large amounts of common ground?

  13. @byron smith said...
    "Sam, I assume you have read the detailed NAS report on the hockey stick graph. How does Montford (NB not Mountford) account for the fact that this report from the most respected scientific body in the US broadly vindicated Mann et. al.?"

    I don't really think it's true that the NAS broadly exonerated Mann et al. (more a case of right for the wrong reasons). I came across this on Brad DeLong's site:

    "Dear Brad:
    I enjoyed skimming through your discussion of the hockey stick. I was a referee on the National Academy Report on the hockey stick (I am named in their report for this service), and so I am very familiar with what the report actually says. It is frequently misrepresented as "verifying" the hockey stick. That is very inaccurate.
    The report concluded that Mann's assertion that there was no medieval warm period was not supported by the data. (Mann really did have an error in his analysis.) The National Academy explicitly concluded that the most we can say about the last 2000 years is that we are now in the warmest period of the last 400 years.

    Actually DeLong, who criticises MM, does say this: "I am definitely a believer in the Medieval Warm Period. In a middle ages in which the stone to build Norwich Castle is shipped by sea from France, it makes absolutely no sense to argue that high costs of transport from France made it efficient to grow wine grapes in England if England then had the same climate that England does today or had in the Little Ice Age." So maybe Mann et al. is plain wrong as well.

    @byron smith said...
    "The Wegman report appears to be a terrible piece of scholarship."


    (July 19, 2006 House Energy and Commerce Subcommittee hearing)
    CHAIRMAN BARTON. [...]Dr. North, do you dispute the conclusions or the methodology of Dr. Wegman’s report?
    DR. NORTH.[NAS report] No, we don’t. We don’t disagree with their criticism. In fact, pretty much the same thing is said in our report.
    CHAIRMAN BARTON. [...]we know that Dr. Wegman has said that Dr. Mann’s methodology is incorrect. Do you agree with that? I mean, it doesn’t mean Dr. Mann’s conclusions are wrong, but we can stipulate now that we have–and if you want to ask your statistician expert from North Carolina that Dr. Mann’s methodology cannot be documented and cannot be verified by independent review.
    DR. NORTH. Do you mind if he speaks?
    CHAIRMAN BARTON. Yes, if he would like to come to the microphone.
    MR. BLOOMFIELD. Thank you. Yes, Peter Bloomfield. Our committee reviewed the methodology used by Dr. Mann and his coworkers and we felt that some of the choices they made were inappropriate. We had much the same misgivings about his work that was documented at much greater length by Dr. Wegman. (

    Roger D.

  14. Byron - I read that, and I'm afraid it confirmed my low view of RC (which I still subscribe to, for some reason). When current events settle down I might do a post explaining why.
    PS just looked at your latest - you lucky git ;)


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