The updated post is here.]
The Climate Audit post Yet Another Upside Down Mann out caused me to write the following remarks about the use of the Lake Korttajarvi, Finland varve proxies in paleoclimate reconstructions.
My generous use of embedded URLs seems to have routed the comment into Spam Purgatory. Despite liberal purchases of Indulgences, it remains there to this day. So, here it is as a blog post.
Update 27 Feb 2010 -- This post assumes the existance of a fictional monastery alongside a fictional "Jarvykortta River" (cf. the real Lake Korttajarvi) in fictional Ruritania (cf. Finland). The point is to explore whether a proxy series can be inadvertantly used in an upside-down orientation. I use this example to illustrate that Yes, such an error is quite possible. I argue that a data series refers back to a characteristic that must only be used in the orientation that makes logical sense with respect to what it represents in the physical world.
I recently returned from a trip to Ruritania. While there, I met with the Abbott of the Jarvykortta Monastery, who told me that the monks have kept a continuous record of the ice breakup date of the adjacent Jarvykortta River since before 400 AD.
It struck me that this could be a useful proxy for the Northern Hemisphere Temperature Anomaly, so I asked if I might have access to these records, and any other information the monastery might have. The Abbott graciously agreed.
The year-by-year record, 389 - 1985 is at BitBucket, as Excel file Jarvykortta-Ice-Out-Proxy.xls.
The date of the Jarvykortta River breakup has been as early as February 15 (in 1231) and as late as June 20 (in 1967). For graphing purposes, I have taken the 11-year rolling average of this series, much as Tiljander et al (2003) did for their varve X-Ray Density data from Lake Korttajarvi, Finland.
I should stress that it was the Finnish Lake Korttajarvi XRD series (Column C in the Excel file) and not this newly-discovered Ruritanian Jarvykortta River series (Column D) that was used by Mann et al (PNAS, 2008) and now, apparently, by Mann et al (Science, 2009).
As with many proxies, there are some potential complications. The Abbott related the following three points to me:
- There is a natural hot spring that empties into the Jarvykortta River, about 1 kilometer upstream of the Monastery. Its flow appears relatively constant, year-to-year. This addition of hot water would make the ice on the river break up earlier than would otherwise be the case.
- Around 1720, a few local farmers began piping some of the hot spring's output to their homes. As the population of the area grew in the 18th and 19th Centuries, this practice became more widespread. This likely led to increasing delays in the timing of the Spring breakup of the river ice by the monastery.
- For much of the 20th Century, the nearby town maintained a skating rink for the winter and spring, just upstream of the monastery. Cooling coils were placed in the river to keep the rink ice solid, well into the spring. In the late 1920s/early 1930s, and again in 1967, hockey playoffs went into late May.
It is difficult to determine how the Ice-Out signal should be related to regional warming or cooling. The Abbott suggested that earlier thaws might generally correlate with milder winters, while late thaws could be due to harsh winters--aside from human effects.
However, a computer program that interpreted rising numbers from 1850 to the present as a signal of regional warming would orient the Ice-Out signal such that earlier ice breakups are correlated with colder temperatures.
Since reliance on complex algorithms is a hallmark of sound experimental practices, I have oriented the Ice-Out proxy in the latter fashion.
The pattern that results is certainly interesting.
I hope this contribution of a novel data series proves helpful in interpreting the Lake Korttajarvi X-Ray Density varve record that was assembled by Tiljander and her colleagues.
It is possible that the two proxies share certain features, as summarized in the one-page summary chart Jarvykortta+Korttajarvi-Proxies.pdf at BitBucket.
UPDATE 2 -- Here's that PDF'd chart at BitBucket as an html table.
|Series||Lake Korttajarvi Varve XRD||Jarvykortta River Ice Breakup|
|Characteristic||X-Ray Densities of Lakebed Sediments||Date of Ice Breakup of River|
|Source||Tiljander et al (2003)||Monastary Abbott|
|Low value||1231: 46 (greyscale)||1231: Feb 15 (46th day of year)|
|High value||1967: 172 (greyscale)||1967: Jun 20 (172nd day of year)|
|Influence of temperature on series?||Yes||Yes|
|Source’s interpretation of temp. effects||Harsher winters lead to mineral-rich varves and higher XRDs||Harsher winters lead to later date of ice breakup|
|Non-temperature natural influences on series?||Yes||Yes|
|Source’s interpretation of non-temp. influences||Higher precipitation increases XRD value||Lesser flow of* hot springs upriver increases date of ice breakup|
|Source’s interpretation of human influences||1720 on, farming increased |
sedimentation and XRD values
|1720 on, diversion of hot springs increased ice breakup dates|
|Known artifacts||Late 1920s: Peat cutting increased XRDs|
1967: Bridge reconstruction increased XRD
|Late 1920s: Skating rink increased ice breakup date|
1967: Hockey final increased ice breakup date
|Source’s summary||Higher XRDs mean lower temps, unreliable post-1720||Later ice breakups mean lower temps, unreliable post-1720|
|Mann et al (2008) |
|Computer screening algorithm |
1850-1995 shows that higher XRDs
must mean higher temps
|Common sense interpretation||Higher XRDs mean lower temps. Unreliable post-1720||Later ice breakups mean lower temps. Unreliable post-1720|
* Lesser flow added as clarification.
** 12/23/09 -- Typo fixed; "1389" to "389".
UPDATE -- The Ruritanian "Jarvykortti River" proxy that I concocted is comprised of a set of numbers that is identical to the actual set of Lake Korttajarvi varve X-Ray Density greyscale values that Mia Tiljander reported in the course of her graduate studies in Finland.
For instance, the X-Ray Density of the varve that was deposited in 1220 was 54. So, in 1220, I had the ice on the Jarvykortta River break up on February 23--the 54th day of the year. In the decade of the 1220s, the ice broke up as early as Feb. 17 (1229), and as late as Feb. 28 (1225).
By contrast, when 170 years had passed, the ice in front of the mythical Jarvykortti Monsastery broke up about 5 weeks later in the season. For the 1390s, the earliest year of the ice breakup was 1395 (March 20), while the latest was 1391 (April 15).
Of course, all of these "ice-breakup dates" are nothing other than the Lake Korttajarvi varve greyscale values, translated by Excel into days-of-the-year.
At first, it sounds plausible when defenders of the Upside-Down usage of the Lake Korttajarvi varve proxies claim that "The higher the varve XRD, the warmer the average temperature has been." After all, who goes through the day thinking about varve densities?
But! This assertion about varves maps directly to the claim that "The later in the season that the river ice breaks up, the warmer the average temperature has been."
Everybody knows that when the winter is warm, ice breaks up early--not late!
Winters at the Jarvykortta Monastery had surely been warmer in the 1220s than they were in the 1390s.
The identical logic lets us know what Mia Tiljander's varve data is telling us about the climate of Lake Korttajarvi in central Finland. It was warmer in the 1220s than it was in the 1390s.
Mann et al's trust in their statistical algorithms have fooled them into thinking that the 1220s must have been cooler than the 1390s.
But the Tiljander proxies are clear: Mann and his colleagues are wrong.
Don't manipulate the data to fit the theory--that's backwards!
[Update 9 March 2010 -- these comments are closed; go here instead.]