http://tallbloke.wordpress.com/2011/11/25/data-errata-caper-cru-methodology-inexplicable/#comment-9862

And who will discover the error if it should happen to exist?

On assigning a meaning of “warmer” or “colder” to increased varve sediment accumulation, Hu wrote,

..lake sediments can go either way, depending on whether they are glacier-fed or snow-fed. Glaciers are there all year round, so a warm year results in lots of melt in the summer and lots of sediment. But if there’s no glacier, a cold winter leads to lots of snow buildup and therefore a massive spring thaw with lots of sediment, so the correlation is the other way around. I believe Tiljander’s Kortjavarti is in the latter category, while many Canadian Rockies lakes are the in the former category. The researcher should indicate the expected correlation with temperature, depending on the siting of the lake.

Tiljander measured total varve thickness (in millimeters) as “thickness”.

She then determined the contribution of inorganics (minerals, in millimeters) as “lightsum”.

She then deduced the contribution of organic matter (in millimeters) by subtracting “lightsum” from “thickness”, to arrive at “darksum”.

The discussion on glacier-fed lakes concerns mineral silt (e.g. rock flour) carried from the glacier to the lake by summer meltwater. This would be Tiljander’s “lightsum”, if Lake Korttajarvi were a glacial lake (as you note, it isn’t). Since there is generally little or no deposition of organic materials in this situation, “darksum” would be negligible. “thickness” would be the same as “lightsum” alone.

I don’t know of a physically-plausible reason for assigning “higher lightsum” to “warmer” and assigning “higher darksum” to “warmer,” as is the case in Mann08.

Using “thickness” as a separate, third proxy appears to be a case of double-counting.

It seems to me to be a case of an honest mistake, due to confirmation bias. I would guess that the authors of Mann08 didn’t think very carefully about these things.

So far as I know, none of the authors have addressed these points, preferring to discuss the similarity of “with Tiljander” and “without Tiljander” reconstructions. Even this not-very-compelling line of reasoning argues against the validity of Tiljander as used in Mann08. This defense was raised again this week, in RealClimate‘s post on Kemp11. I discussed it here.

You say:

But if there’s no glacier, a cold winter leads to lots of snow buildup and therefore a massive spring thaw with lots of sediment, so the correlation is the other way around. I believe Tiljander’s Kortjavarti is in the latter category

and

The researcher should indicate the expected correlation with temperature, depending on the siting of the lake.

Good point, but we don’t need to guess where the lake in question is.
Here is a Google map link showing the location of Lake Korttajärvi in Finland. The country has a generally low elevation and there are no nearby mountains with glaciers sourcing major rivers that cross Western Finland, so you are right, the lake is in the latter category.

I disagree with AMac that Mann’s responses were uninformative. They were informative and misleading. Mann is essentially saying that his program would flip Tiljander to the correct orientation so it is not possible to use it upside-down. This is both incorrect in the CPS case, and irrelevant to the point Steve McIntyre made, that the proxy cannot be used because the modern portion is diverging.

That PNAS Letter by Mann et al. is a rebuttal of a short comment that McIntyre and McKitrick had published in PNAS, critical of Mann08. It is part of a lengthy saga.

For the paragraph concerning Tiljander, much has been written. Brief comments –

The claim that ‘‘upside down’’ data were used is bizarre.

This is an uninformative statement.

Multivariate regression methods are insensitive to the sign of predictors.

That may be for EIV and/or for CPS, but the claim is not responsive to the issue at hand: whether lightsum and XRD were employed in Mann08 such that data values assigned by Tiljander03 to “warmer conditions” were inadvertantly assigned by Mann08 to “colder conditions” (they were).

Screening, when used, employed one-sided tests only when a definite sign could be a priori reasoned on physical grounds.

Again, that may be, but the claim is not responsive to the issue at hand.

Potential nonclimatic influences on the Tiljander and other proxies were discussed in the SI,

This is correct.

which showed that none of our central conclusions relied on their use.

Mann et al. are asserting that the material in the SI showed that none of Mann08′s central conclusions relied on the use of the Tiljander proxies. This claim is hotly disputed. Even the definition of “the contents of the SI” has been the subject of dispute. A revised version of one key figure, S8A, replaced Fig. S8A after publication of Mann08. The original is still at pnas.org, to my knowledge, with the revision at Prof. Mann’s website. The revision was then subsequently re-revised. The SI of Mann09 then revisited some claims made in the SI of Mann08, weakening them.

Mann responded to a question I asked on behalf of AMac about the Tiljander issue. He responded with an update that included a link to a (fairly negative) comment he made on a paper by McIntyre & McKitrick in PNAS.

http://www.meteo.psu.edu/~mann/shared/articles/MMReplyPNAS09.pdf

I imagine you read that and responded in some way. Do you know of a good summary of this issue and the status of the issue today?

Best,
Alex Harvey

Voldemort’s Question