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Thread: The new hockeystick doubles recorded temperature?

  1. #1 The new hockeystick doubles recorded temperature? 
    Forum Sophomore andre's Avatar
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    The new hockeystick is here


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    the abstract:

    Following the suggestions of a recent National Research Council report [NRC (National Research Council) (2006) Surface Temperature reconstructions for the Last 2,000 Years (Natl Acad Press, Washington, DC).], we reconstruct surface temperature at hemispheric and global scale for much of the last 2,000 years using a greatly expanded set of proxy data for decadal-to-centennial climate changes, recently updated instrumental data, and complementary methods that have been thoroughly tested and validated with model simulation experiments. Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats. The reconstructed amplitude of change over past centuries is greater than hitherto reported, with somewhat greater Medieval warmth in the Northern Hemisphere, albeit still not reaching recent levels.
    They use two methods of reconstruction:

    ...Most attempts to reconstruct hemispheric temperatures have used some variant on the ‘‘composite plus scale’’ (CPS) methodology (10), in which proxy data (such as tree rings, ice cores, or corals) considered to be sensitive to past surface temperature variations are standardized and centered, potentially weighted, and then composited to form a regional or hemispheric series,...

    recently, Hegerl et al. (13) use a weighted composite of proxy temperature series, but scaling is accomplished by a so-called ‘‘error-in-variables’’ (EIV) regression method (‘‘total least squares’’) to allow for errors in both predictors (i.e., proxy composite) and predictand (i.e., the instrumental hemispheric mean temperature series)....
    About those methods they observe:

    The skill diagnostics (Fig. 2; see also Dataset S4) for the validation experiments indicate that both the CPS reconstructions (with the screened network) and EIV reconstruction (with the full network) produce skillful NH land reconstructions back to A.D. 400. When tree-ring data are eliminated from the proxy data network, a skillful reconstruction is possible only back to A.D. 1500 by using the CPS approach but is possible considerably further back, to A.D. 1000, by using the EIV approach. We interpret this result as a limitation of the CPS method in requiring local proxy temperature information, which becomes quite sparse in earlier centuries. This situation poses less of a challenge to the EIV approach, which makes use of nonlocal statistical relationships, allowing temperature changes over distant regions to be effectively represented through their covariance with climatic changes recorded by the network.
    So looking at the reconstruction we see the EIV showing a distinct medieval warm period and what also bugs a bit is the addition of the instrumental records, showing a increase of about 1.3 degrees over the last century:



    The normal temperature increase used to be about 0.6 degrees per century (for instance Folland et al.

    What also seems to be strange is the increasing deviation between those temperature records and the reconstruction, staying clearly behind in the last part of the graph.

    Now see what happens if we remove those "recorded" temperatures:


    Click to see full size image

    See that the temperature range of the reconstructions are indeed close to 0.6 degrees in the last century. So it would be interesting to see where that 1.3 range comes from.

    Note also that the reconstructions without those instrumental records do not support the claim:

    ...We find that the hemispheric-scale warmth of the past decade for
    the NH is likely anomalous in the context of not just the past 1,000 years, as suggested in previous work, but longer...


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    "See that the temperature range of the reconstructions are indeed close to 0.6 degrees in the last century. So it would be interesting to see where that 1.3 range comes from."

    It comes from the margin of error: + or - 5% When looking at data of any kind, always ask, "What is the margin of error?" Temperatures could be falling a tick rather than rising a tick.

    Proponents of global warming will show the upper extreme of the margin of error in their charts, whereas, opponents will choose the lower extreme. Whoever screams and beats their drum the loudest will get their politicians elected.


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    Quote Originally Posted by williampinn
    It comes from the margin of error: + or - 5% When looking at data of any kind, always ask, "What is the margin of error?" Temperatures could be falling a tick rather than rising a tick.
    .
    Really, quoting:

    the best linear fit to annual global surface temperature gives an increase of 0.61 ± 0.16°C between 1861 and 2000.
    Not much room for margin
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    Not sure what your point is, or what you find unusual. Why would you want to remove the recorded temperatures? Their margin of error and temporal resolution are much better than the proxy data used by the numerous reconstructions.
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    The first point is that Mann et al add "instrumental" records which are more than double the warming over the last century than reported by other studies.

    The second point is that the variation of the reconstruction over the last century matches this warming already.

    Conclusion something very fishy here.
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    Quote Originally Posted by andre
    The first point is that Mann et al add "instrumental" records which are more than double the warming over the last century than reported by other studies.

    The second point is that the variation of the reconstruction over the last century matches this warming already.

    Conclusion something very fishy here.
    It's good that you are keeping your eyes open. Selling carbon credits might motivate some to fudge the numbers a bit. Satellite data has only been around for a short while, so the dataset is extremely small. The predictions made regarding climate will easily fall prey to the butterfly effect. In short, no one really knows the future. There are only people who think they know and/or want you to believe they know.
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  8. #7  
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    Quote Originally Posted by andre
    The first point is that Mann et al add "instrumental" records which are more than double the warming over the last century than reported by other studies.
    And? As already stated the proxy data is of less temporal resolution, bore hole temperatures for example smooth over decades and lag the surface temps. Lake and ocean sediments have an even lower time resolution.

    The second point is that the variation of the reconstruction over the last century matches this warming already.
    Don't see your point here. Uncertainties in the proxy data generally become larger as one goes back in time.
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