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Myth vs. Fact Regarding the "Hockey Stick"

Filed under: — mike @ 4 December 2004 - (English)

Una traducción está disponible aquí.

9 Responses to “Myth vs. Fact Regarding the "Hockey Stick"”

  1. 1
    Saheli says:

    Thanks! This is a great resource!

  2. 2
    Stephen Berg says:

    Holy cow!!! What a great site! Way to go and keep it up!

  3. 3

    When Climatologists Attack!!
    The climatologists are angry, and are on the warpath against the industry-funded Tech Central Station: RealClimate » Temperature Variations in Past Centuries and the so-called "Hockey Stick": …coined by the former head of NOAA’s Geo…

  4. 4
    John Finn says:

    I have a yet another question.

    In the above article you discuss various myths associated with the “hockey stick” graph. To support your argument you refer to other sources. For example “see Cook et al 2004” at the end of the myth 1 discussion. So I thought – ok, I’ll look up the Cook study and see what it says. Now unfortunately I’m a total non-expert – I only started reading about climate change a few months ago, so it always possible that I’ve misunderstood something. Anyway as I was reading the paper it struck me that neither the Cook study – nor any of the other proxy studies were in total agreement with the hockey stick.

    [Response: Your comment is somewhat incorrectly premised. There is no uniquely defined ‘hockey stick’ reconstruction. This term, as defined in our glossary, refers to the general shape, common to a number of independent reconstructions (see this comparison of various proxy- and model-based estimates), characterized by 20th century large-scale warming that exceeds the bounds of the more moderate temperature variations characterizing preceding centuries. The details of any individual reconstruction depend, however, on the regions and seasons represented by that particular reconstruction, as discussed above in the discussion of “myth #1”. In the Cook et al (2004) paper referred to above, the authors are indeed careful to emphasise that their conclusions pertain to the warm-season and extratropical, continental region represented by their particular reconstruction. There are a number of important reasons why reconstructions differ depending on seasonal and spatial sampling considerations (see the response to comment#3 above, and also the discussion in the review paper by Jones and Mann (2004–see section 5.3 therein) [Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi: 10.1029/2003RG000143, 2004.]. It is therefore not surprising that past summer, extratropical temperature changes, such as are reconstructed by Esper et al (2002) and Cook et al (2004), may indeed have differed significantly from annual temperature changes over the entire (tropical and extratropical) Northern Hemisphere, such as are targeted in other reconstructions (e.g. Jones et al, 1998; Mann et al, 1999; Crowley and Lowery, 2000; Mann and Jones, 2003). Despite these differences in seasonal and spatial emphasis, however, the various reconstructions and model estimates are in fact observed to be consistent within estimated uncertainties. -mike]

    You could argue that all the reconstructions show some agreement up to about 1980 – but after that the measured temperature record diverges completely from the proxy records and by the end of the century appears to be at least 0.3 degrees higher than the proxies.

    [Response: This is not correct. Most reconstructions only extend through about 1980 because the vast majority of tree-ring, coral, and ice core records currently available in the public domain do not extend into the most recent decades. While paleoclimatologists are attempting to update many important proxy records to the present, this is a costly, and labor-intensive activity, often requiring expensive field campaigns that involve traveling with heavy equipment to difficult-to-reach locations (such as high-elevation or remote polar sites). For historical reasons, many of the important records were obtained in the 1970s and 1980s and have yet to be updated. The fact that a relatively small number of long high-resolution proxy temperature records extend through the most recent decades should not be mis-interpreted as evidence against recent warming (as sometimes done by certain contrarians). The available long records that extend through the present typically do indeed confirm the recent warming. For example, through a composite of the relatively few very long available proxy records that extend all the way through the 1990s, Jones and Mann (2004) show that proxy-reconstructed Northern Hemisphere temperatures [navy blue curve in Figure 2 here, do indeed reproduce the post-1980 warming indicated by the instrumental record (red curve in same figure). -mike]

    As I say I thought this was down to me as I hadn’t seen anything – even in sceptic articles which mentioned this. However towards the end of the paper, it refers to the difference between the Cook (or Esper) reconstruction and the observed temperature, saying

    “Note that it does very well at tracking the instrumental data on inter-decadal and longer tinescales up to about 1982, after which the tree-ring estimates systematically under-estimate the actual warming. ”

    There are probably several possibilities for this, but the two most obvious would be
    1. The Surface Temperature is wrong – at least after 1980 or
    2. The proxy measurements do not accurately reflect true temperature, i.e. there is a
    ‘damping’ effect.

    [Response: This comment again reflects some degree of misunderstanding regarding what the proxy reconstructions and instrumental data actually show. There is no discrepancy in general between the 20th century trends indicating by the instrumental record and by most proxy reconstructions. In some tree-ring reconstructions (particularly, those based on tree-ring density information, and emphasising higher latitudes), however, anomalous behavior in recent decades apparently related to non-climatic (or, at least, non-temperature related) influences on tree growth does indeed compromise the use of these data in reconstructing temperature changes over the past several decades [see e.g. the discussions by Briffa et al (1998)[Briffa et al, Reduced sensitivity of recent tree-growth to temperature at high northern latitudes, Nature, 391, 678 – 682 (1998)] and also this article in Eos by Mann et al (2003)[Mann, M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J. T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., Response to Comment on ‘On Past Temperatures and Anomalous Late 20th Century Warmth’, Eos, 84, 473, 2003]. The same factors may compromise the behavior of the Esper et al (2002)/Cook et al (2004) reconstructions in recent decades as well. These factors, however, do not appear to be relevant to other, multiple-proxy based reconstructions such as those referred to above. -mike]

    Whatever the reason for the divergence, it would seem to suggest that the practice of grafting the thermometer record onto a proxy temperature record – as I believe was done in the case of the ‘hockey stick’ – is dubious to say the least.

    [Response: No researchers in this field have ever, to our knowledge, “grafted the thermometer record onto” any reconstruction. It is somewhat disappointing to find this specious claim (which we usually find originating from industry-funded climate disinformation websites) appearing in this forum. Most proxy reconstructions end somewhere around 1980, for the reasons discussed above. Often, as in the comparisons we show on this site, the instrumental record (which extends to present) is shown along with the reconstructions, and clearly distinguished from them (e.g. highlighted in red as here). Most studies seek to “validate” a reconstruction by showing that it independently reproduces instrumental estimates (e.g. early temperature data available during the 18th and 19th century) that were not used to ‘calibrate’ the proxy data. When this is done, it is indeed possible to quantitatively compare the instrumental record of the past few decades with earlier estimates from the proxy reconstruction, within the context of the estimated uncertainties in the reconstructed values (again see the comparisons here, with the instrumental record clearly distinguished in red, the proxy reconstructions indicated by e.g. blue or green, and the uncertainties indicated by shading). -mike]

    Have you any comments on this?

    [Response: See above. -mike]

  5. 5
    John Finn says:

    In your responses above, you say

    “Most proxy reconstructions end somewhere around 1980, for the reasons discussed above….”

    Then why does the Cook paper comment on the “under-estimation of actual warming after 1982”. There is a graph (at the top of Page 2) which shows the proxy reconstructions extending well beyond 1980. I have just looked at the Briffa study (also referenced by yourselves) which also shows reconstructions beyond 1980.

    [Response: Please carefully read the response to your previous post. Further information is provided in the Jones and Mann (2004) review paper, which is linked to above. Unfortunately, due to other demands on our time, this will have to be the last word on the matter for the present. -mike]

    You also say

    “While paleoclimatologists are attempting to update many important proxy records to the present, this is a costly, and labor-intensive activity….”

    While this may be true I would have thought that this would be seen as a major priority in order to provide confirmation and validation of the surface temperature record. After all, this is the period which is supposed to show ‘unprecedented’ warming surely it’s necessary to obtain as much evidence as possible to confirm this.

    There doesn’t seem to be the same problems when it comes to validating (or not) the UAH satellite record.

  6. 6
    John Finn says:

    I accept you know longer wish to discuss this but I would like to comment on part of your previous responses where you say

    “…however, anomalous behavior in recent decades apparently related to non-climatic (or, at least, non-temperature related) influences on tree growth does indeed compromise the use of these data in reconstructing temperature changes over the past several decades”

    This seems like incredible bad luck. Here we have a perfectly reliable method for reconstructing past temperatures over hundreds of years – then all of a sudden there is “anomalous behavior in recent decades apparently related to non-climatic (or, at least, non-temperature related) influences on tree growth”. And wouldn’t you know it – this anamalous behaviour coincides exactly with a period of ‘unprecedented’ warming.

    [Response: These are exactly the types of issues that paleoclimatologists worry about, and spend a great bit of time attempting to deal with. The phenomenon in question gets at the issue of “uniformitarianism” that is that the heart of proxy methods for reconstructing past climates. Proxy-specific biases are, for example, one argument in favor of the use of multiple proxy indicators in reconstructing past climates. A good discussion of all of these issues can be found in the Jones and Mann (2004) review paper referred to in comment #4 above. I hope you find this reference of some help in answering other questions you may have.]

  7. 7
    mike says:

    “Myth #0” added 12/23/04 -mike

  8. 8
    Eli Rabett says:

    Well, if nothing else, the perturbation of atmosphere and water supplies have certainly been a lot greater in the last 20-50 years than previously. So, as we were saying, we do know that atmospheric composition or the trace gases (everything but O2, N2 and maybe Ar) has changed rapidly in the past half century, maybe a little more, maybe a little less. OTOH, unless you have some information not available to me, these have been relatively stable pre 1900 back at least a few millenia, at least in comparison with recent times.

    So why are you surprised that tree growth patterns have altered lately and what would you attribute this to? We do know that northern forests, for example, have been affected by sulphate emissions. I would regard this not as an indicator that the proxy records have been falsified, but that anthropic effects are clearly visible in the recent records.

  9. 9

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