The last post in this series showed Michael Mann’s 2008 paper depended entirely upon the use of two things: tree ring data and the Tiljander series. It also showed those Tiljander series were suspect. Today I’ll show they are worse than suspect. Michael Mann’s use of them was absurd.
The two methodologies Mann used to create temperature reconstructions (CPS and EIV) both require data be calibrated against modern temperatures. The idea is simple. If a series doesn’t track temperatures in modern times, we can’t expect it to track temperatures in the past. The problem is the Tiljander series could not possibly be calibrated against modern temperatures. The lead author of the paper explicitly states:
Since the early 18th century, the sedimentation has clearly been affected by increased human impact and therefore not useful for paleoclimate research.
If the data since the early 18th century isn’t useful for paleoclimate research, one cannot justify calibrating the series to the modern temperature record for the 19th and 20th centuries. Mann didn’t contradict the authors’ when they said the modern portion of the Tiljander series were contaminated, but we saw in the last post he was aware of their concerns.
Mann knew the Tiljander series were contaminated in a way that made it impossible to calibrate the series to the modern temperature record, yet he still used them in methodologies which required the series be calibrated to the modern temperature record. It should come as no surprise this led to nonsensical results.
There are four Tiljander series: Lightsum, Darksum, Thickness and XRD (X-ray Density). Well, there aren’t really four. You see, Thickness and XRD are measured. The thickness of a sample is easily measured (such as with a caliper). An x-ray is then taken. Like in all x-rays, there is some light and some darkness in the result. The relationship between them gives a “density,” which is just the ratio of light to dark.
Lightsum and Darksum are just the total amounts of light and darkness. That’s easy to calculate if you know the proportions of light and dark (given by XRD), and you know the total thickness. You just multiply. If the thickness was 10, and the ratio is 60% light/40% dark, you’d have 6 light, 4 dark. (Actual formulas for the process can be found here.)
Of course, multiplying Thickness and XRD doesn’t magically give you twice as much data. It doesn’t give you twice as much information. You can’t just modify a series over and over and reuse it each time. Mann was wrong to use all four series.
But whatever. Let’s get back to the nonsensical results Mann got by deciding to calibrate proxies that didn’t reflect temperatures in the modern period to the modern temperature record. A question you should ask yourself about these series is, “What do higher values mean?” Instinctively, you might think a higher value means higher temperatures. However, if we’re measuring something like the amount of ice, higher temperatures might lead to lower values. According to Mia Tiljander:
High X-ray density corresponds to high amount of mineral matter (light grey value tints in X-ray film) and low X-ray density corresponds to
dark grey values caused by a higher proportion of organic matter.
High XRD means high Lightsum. Low XRD means high Darksum. As you can see, Lightsum and Darksum must have opposite patterns. High values in one must indicate low values in the other. That means if high values in one indicate warmer temperatures, high values in the other must indicate cooler temperatures. And no matter what, XRD and Lightsum must indicate the same thing.
Additionally, high amounts of mineral matter mean high Lightsum and XRD values. High amounts of organic material mean high Darksum values. With that in mind, we can continuing reading what Tiljander says:
The layer above the mineral matter is defined as organic, because of the less dense structure in X-ray images and low grey-scale values. A thick organic lamina probably indicates a warm summer and a relatively long growing season.
Tiljander says thicker organic layers (lamina) indicate higher temperatures. That means higher Darksum values indicate warmer temperatures while higher Lightsum/XRD values indicate lower temperatures. Thickness won’t have any coherent climatic interpretation since its the sum of Lightsum and Darksum.
Now then, suppose we tried to calibrate these series to the modern temperature record. We’d expect Darksum to have a positive correlation, Lightsum and XRD to have a negative correlation and Thickness to have no correlation. Mann found otherwise. The correlations he got when using his CPS methodology were:
Darksum: 0.3066 Lightsum: 0.2714 Thickness: 0.2987 XRD: 0.1232
All four correlation coefficients are positive. That means Mann concluded higher values indicate higher temperatures for all four series. He found a “temperature signal” in a series with no climatic information (Thickness), and he found “temperature signals” the opposite of what we’d expect in two series (Lightsum and XRD).
How’d that happen? Simple. All four series had high values in recent times because they had been “affected by increased human impact.” That human impact caused recent values in all four series to be abnormally high. Mann took that as indicating all four series show warming. This shows when you use data that is “not useful for paleoclimate research,” you get nonsensical results.
But then there’s the EIV methodology. It’s more complicated, but you should remember from our discussion of Mann’s original hockey stick that temperature reconstructions are often done in “pieces.” Different data is available over different periods so they do calculations over different periods and stitch the results together. Let’s look at how the Tiljander series were used in two different periods. In the period beginning at 500 AD (graphs courtesy of Climate Audit regular UC):
We see all four show the same relationship as the CPS methodology – higher values indicate higher temperatures. That’s obviously wrong. However, there’s something stranger. This is the same image for the period beginning at 600 AD:
The XRD series is now flipped over. For this period, higher XRD values indicate lower temperatures. Not only does Mann use the data opposite its physical interpretation, he uses it opposite his own interpretation.
As I said, nonsensical results.