NOT SO GREEN  |  Well, That's Settled !

By steven d keeler | Jan 27, 2016
Source: Unknown


A Model-Based Approach to Climate Reconstruction Using Tree-Ring Data

Dendrochronology is not a “ pseudo science, ” Mann and Jones’ misapplication of a useful scientific tool – more than one actually, since they also misuse statistics – is the pseudoscience. It would help if folks would actually learn just what the word refers to. All dendrochronology can do is tell you when something happened, not why. That is the error and strawman that much of the “ hockeystick ” argument is based on. Mann et al. assumed they knew “ why ” tree grow varies, then proceeded from there. Then they discovered that the MWP was visible in tree rings and that lead to the famous statement regarding getting rid of the MWP. Now at least Briffa is admitting that the factors that influence tree growth are more complex than simply temperature.

Study Here

Trees were selected because their recent ring thicknesses correlated with temperatures in a recent time period called the ‘calibration range’. It was assumed that the ring thickness of the selected trees are indicators of past temperatures. Therefore, ring thicknesses of those trees were used as indicators of temperatures prior to the calibration range.

However, there is no reason to accept the assumption. If the variations in ring thicknesses are random then some trees would provide ring thicknesses that correlate to temperature in a ‘calibration period’ so would be selected as temperature indicators. But different trees would be selected if a different ‘calibration period’ were used. In this case of random variations to ring thickness, the indications of past temperatures would be wrong but how wrong would be a random result.

And the real situation is worse than the described random case because it is not reasonable to assume that temperature has so large an effect that it overwhelms all the other variables which affect growth of tree rings. Several variables (e.g. territory marking by animals, growth or death of nearby light obscuring plants, soil moisture, etc.) may provide temporary alterations to growth of rings which overwhelm effect of temperature. In this – probably the real – case, the indications of past temperatures would be wrong and how they are wrong would depend on how local circumstances changed.

The fact that dendrochronolgy is demonstrated to work as a local dating method is clear evidence that local variables do provide temporary alterations to growth of tree rings which overwhelm effect of temperature.

At the end of the paper ( Study ) they say this, which is worth reading:

Message for the paleoclimate community

We have demonstrated model-based approaches for tree-ring based reconstructions that are able to incorporate the assumptions of traditional approaches as special cases. The modeling framework allows us to relax assumptions long used out of necessity, giving flexibility to our model choices.  ... However, if we are unsure whether the assumptions are correct and there are other assumptions equally plausible a-priori, we will have unrecognized uncertainty in the predictions. We believe that such uncertainty should be acknowledged when using standardized data and default models. ... We believe that such model uncertainty needs to be recognized by the community as an important source of uncertainty associated with predictions of historical climate. The use of default methods makes evaluation of such uncertainty difficult.

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