Wegman and Rapp on proxies: A divergence problem, part 2

Recent posts on the Wegman Report and Donald Rapp’s Praxis-Springer text book Assessing Climate Change have generated much comment. In A Divergence Problem, part 1, I noted  that the sub-section on dendrochronology (tree ring-proxies) in Rapp’s book was based in large part on nearly verbatim material found previously in the Wegman Report. That in turn was a somewhat distorted summary of material found in Raymond Bradley’s seminal text book, Paleoclimatology: Reconstructing Climates of the Quaternary.

In this follow up post, I”ll examine the Wegman’s treatment of other proxies, which were also derived from Bradley.  I’ll also take a closer look at the three proxy sub-sections in Rapp that are derived in turn from Wegman. In all three cases,  divergences are slight, but do include some interesting changes in the references.

Like the last time, the following discussion of Wegman is based on a side-by-side comparison of Wegman and Bradley (PDF).  Unlike the tree-ring case, which included additions and divergences (see previous PDF), Wegman’s sections on ice core and coral proxies appear to be based on a close following of Bradley’s text (except as noted below). Some sentences are paraphrases, while others follow Bradley’s wording quite closely indeed.

For example, here’s Wegman on ice cores (at p. 14):

The transition from snow to firn to ice occurs as the weight of overlying material causes the snow crystals to compress, deform and recrystalize in more compact form. As firn is buried beneath subsequent snowfalls, density is increased as air spaces are compressed due to mechanical packing as well as plastic deformation. Interconnected air passages may then be sealed and appear as individual air bubbles. At this point the firn becomes ice.

Here’s the corresponding passage from Bradley (footnote 10, in section 5.1):

The metamorphism of snow crystals into firn and eventually ice occurs as the weight of overlying material causes crystals to settle deform, and recrystallize, leading to an overall increase in unit density. When firn is buried beneath subsequent snow accumulations, density increases as air spaces between the crystals are reduced by mechanical packing and plastic deformation until … interconnected air passages between grains are sealed off into individual air bubbles (Herron and Langway, 1980). At this point, the resulting material is considered to be ice.

Note: As before, italics represent sections of paraphrase summary, while regular font indicates sections of substantial commonality of wording.

While there can be no doubt that these sections are in the main derived from Bradley, they appear to be a fairly straightforward recitation of the material (unlike the tree-ring proxy section). It should be noted, however, that the final sentences in both Wegman’s sections on ice core and on corals have no clear analogue in Bradley. For example, although Bradley does touch on atmospheric composition, the provenance for the last sentence in Wegman on ice cores remains unclear:

The relative atmospheric concentrations of greenhouse gases as well as aerosol and particulate content coupled with other climate information gives insight into both the importance of these as drivers of temperature as well as how these drivers might couple in either a positive or negative feedback sense.

Turning now to Rapp’s use of the Wegman proxy passages, we can easily see that extensive material has been incorporated verbatim, with little change. Because the Rapp text follows Wegman so closely, a side-by-side comparison is unnecessary. Rather I have reproduced and annotated sections 1.1.1.1 (tree-rings), 1.1.1.2 (ice cores) and 1.1.1.6 (corals) (see PDF).  In the main, Wegman meaterial has been incorporated verbatim, with minor changes such as slight wording (e.g. “challenge” instead of  “problem”) or the addition of hyphens (“paleo-climatology”, not “paleoclimatology”).

However, there have been changes relating to attribution, of which I will give several examples. As before, bold indicates additions in Rapp, while strikethrough indicates Wegman wording removed in Rapp.

The long verbatim section from Wegman in Rapp’s section 1.1.1.1. (tree ring proxies) has had two references removed:

Maximum density values are strongly correlated with April to August mean temperatures in trees across the boreal forest from Alaska to Labrador, Schweingruber et al., (1993) …

Photosynthetic processes are accelerated with the increased availability of carbon dioxide in the atmosphere and, hence, it is conjectured that ring growth would also be correlated with atmospheric carbon dioxide; see Graybill and Idso (1993).

The first removed reference was a carryover from Bradley; the second was a Wegman addition, as noted in Part 1.

The rest of the changes involve the addition of references. Here is a passage from section 1.1.1.1 (tree rings):

The assumption in this inference is that when the tree ring structure observed during the instrumented period that is similar to the tree ring structure observed in the past, both will have correspondingly similar temperature profiles (Beckman and Mahoney, 1998).

However, as As pointed out earlier, many different sets of climatic conditions can (and do) yield similar tree ring profiles. Thus, tree ring proxy data alone is not sufficient to determine past climate variables (Mann, Bradley, and Hughes, 1998).

Somehow, two references have been added that were not present in Wegman. The Beckman and Mahoney reference is to an article The Maunder Minimum and Climate Change: Have Historical Records Aided Current Research ? [PDF] (ASP Conference Series, Vol. 153, 1998). That article discussed Eddy’s use of the tree-ring 14C record as an inversely correlated proxy indicator for sunspot activity, but does not appear to be relevant to a discussion of tree-rings as a temperature proxy.

The second reference is, of course, the first MBH Nature paper, Global-scale temperature patterns and climate forcing over the past six centuries. That paper does state the advantages of the multi-proxy approach:

Moreover, the mutual information contained in a diverse and widely distributed set of independent climate indicators can more faithfully capture the consistent climate signal that is present, reducing the compromising effects of biases and weaknesses in the individual indicators.

However, the supposed issue that “different sets of climatic conditions can (and do) yield similar tree ring profiles” is not raised as a potential weakness of tree-ring proxies. Moreover, in his text book on paleoclimatologhy, MBH co-author Bradley contradicted the contention that “tree ring proxy data alone is not sufficient to determine past climate variables”, stating:

If an equation can be developed that accurately describes instrumentally observed climatic variability in terms of tree growth over the same interval, then paleoclimatic reconstructions can be made using only the tree-ring data. [Emphasis added]

Rapp’s sections on ice cores and corals both end with sentences from Wegman that have no obvious analogue in Bradley (as previously noted). And, once again, Beckman and Mahoney has been added as the reference in Rapp’s version.

The relative atmospheric concentrations of greenhouse gases as well as aerosol and particulate content coupled with other climate information gives insight into both the importance of these as drivers of temperature as well as how these drivers might couple in either a positive or negative feedback sense (Beckman and Mahoney, 1998).

…

Thus, not unlike tree rings, data on corals also can be calibrated to estimate (sea) surface temperatures (Beckman and Mahoney, 1998).

And, once again, there is no apparent connection between these passages and the given reference.

That concludes (finally!) my analysis of passages in common between the Wegman report and chapter 1 of Donald Rapp’s Assessing Climate Change.

I will be doing one more post on other issues in Rapp, as well a post on the publisher Praxis-Springer. I will also be returning to the Wegman report, but with renewed emphasis on its context.