It’s "interesting times" at realclimate.org where the authors feel the need suddenly to check their sources and the provenance of data in a way that they clearly didn’t before, and advise caution when the latest scare stories of global warming come in.
For students of psychology, this points to an internal conflict of the psyche between the conscience on the one hand and deeply held beliefs on the other. What, I wonder, would a psychologist have made of the post entitled "What if…the Hockey Stick were wrong?" published on the 27th January 2005, the day that the MM05 results were published?
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This is an interesting and amusing comment on factor analysis, a technique very closely related to principal component analysis: J. Scott Armstrong, Derivation of Theory by Means of Factor Analysis or Tom Swift and His Electric Factor Analysis Machine, The American Statistician, 1967, 17-21 Link
This is the first replication note that gets into the meat of our emulation. Previously we’ve noted the non-replicability of certain MBH98 steps, but, since relevant intermediate calculations were archived, we were able to proceed using the archived intermediate calculations. Here we show the key replication step calculating “reconstructed [temperature] principal component” series. Archiving is incomplete. However, we have figured out the mechanics of 5 archived RPCs and have achieved a reasonably accurate replication. However, there are puzzling breakdowns, including a substantial and unexplained difference in the controversial early 15th century, which we do not believe can be resolved without examining source code. Continue reading →
Khim et al. [2002] reported that a core from the Eastern Bramsfield Basin, Antarctic Peninsula showed that the LIA and MWP were the strongest of the Late Holocene cold and warm periods. Continue reading →
Millar, Constance, Robert Westfall, Diane Delany, John King and Harry Alden, Climate As An Ecosystem Architect; Responses Of High-Elevation Conifers To Past Climate Variability. Continue reading →
Here’s an interesting comment from an applied statistician about principal components: Continue reading →
A few comments on Mann’s interview on BBC4 in which Ross McKitrick and I were discussed.
Given the seeming efforts to backpedal on the role of the hockey stick in promoting Kyoto, it was interesting to hear the BBC reporter state that it was "hard to over-estimate how influential that study [MBH98] and that image [the hockey stick] has been".
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One of the fun parts about finding the Hockey Stick is the many guises in which it appears. If you didn’t know what you were looking at, you could easily miss the significance of the information provided for you by people in authority.
Today’s scientific authority is the government of New Zealand.
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The calculation of temperature PC series needs to be distinguished from the calculation of tree ring PC series. Procedures for the handling of missing data in the temperature dataset were described in the MBH98 Corrigendum SI for the first time in July 2004, specifying that linear interpolation was done, but not specifying the handling of missing data at the beginning and end of records.
I show here a fairly close replication of MBH98 results from the temperature dataset archived in July 2004 at the Corrigendum SI. Unlike tree ring PC networks, stepwise methods were almost certainly not used for temperature principal components. Also, centered calculations appear to have been used for temperature PC series, but were not used for tree ring PC series. von Storch et al. [2004] pointed out that MBH98 incorrectly used weight of the cosine of the latitude, rather than the square root of the cosine of the latitude, but did not show the specific effects of the error on MBH98 temperature PC series.
Here I show that the error leads to significant differences in the temperature PC series after the first few series. Link
The Wall Street Journal published this editorial last Friday, on the Hockey Stick controversy and the work of Steve McIntyre:
Hockey Stick on Ice
Politicizing the science of global warming.
Friday, February 18, 2005 12:01 a.m. EST
On Wednesday National Hockey League Commissioner Gary Bettman canceled the season, and we guess that’s a loss. But this week also brought news of something else that’s been put on ice. We’re talking about the "hockey stick."
Just so we’re clear, this hockey stick isn’t a sports implement; it’s a scientific graph. Back in the late 1990s, American geoscientist Michael Mann published a chart that purported to show average surface temperatures in the Northern Hemisphere over the past 1,000 years. The chart showed relatively minor fluctuations in temperature over the first 900 years, then a sharp and continuous rise over the past century, giving it a hockey-stick shape.
Mr. Mann’s chart was both a scientific and political sensation. It contradicted a body of scientific work suggesting a warm period early in the second millennium, followed by a "Little Ice Age" starting in the 14th century. It also provided some visually arresting scientific support for the contention that fossil-fuel emissions were the cause of higher temperatures. Little wonder, then, that Mr. Mann’s hockey stick appears five times in the Intergovernmental Panel on Climate Change’s landmark 2001 report on global warming, which paved the way to this week’s global ratification–sans the U.S., Australia and China–of the Kyoto Protocol.
Yet there were doubts about Mr. Mann’s methods and analysis from the start….
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Climate Audit 
A Reader's Comment about Principal Components
Here’s an interesting comment from an applied statistician about principal components: Continue reading →