Cowtan and Way – The Magician's 'Red Scarf Trick' with Linear Trend Lines

Guest Post by Kip Hansen

There are a lot of good, in-depth technical discussions of Cowtan and Way 2013, Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends. This is not one of them. In this post, I only hope to demonstrate a trick I learned when a young man, when I was a semi-professional performing magician. It is meant to be fun even though is makes a very valid and necessary point. I will use C&W 2013’s results graphic from their Media Summary:

Caption: “Temperature data from the Met Office (thin lines) compared to the optimal Cowtan and Way (2013) global reconstruction (thick lines). The straight red lines indicate the trend over the past 16 years in the respective data. The background image illustrates the coverage of the Met Office data, with colours indicating geographical temperature trends. The Arctic is warming much faster than the rest of the planet.”

It is followed by the statement: 

“The temperature change for any individual year is not very large (and less than the Met Office uncertainty estimates), but together they make a significant difference to recent temperature trends. This highlights the danger of drawing conclusions from trends calculated over short periods.”

As in all good performances of the Magician’s Art – you may have failed to notice that the trick has already taken place. You can read the amazement in the MSM and on the climate blogs – they are all agog at the marvelousness of it. Even their detractors [for the most part, there are exceptions] and the skeptical, see clearly that a low bias in determining missing surface temperature values in the Arctic has caused Global Temperatures to be understated.

Now, please, I make no claims as to the intentions of Cowtan and Way. I only claim to illustrate a simple little point using their recent paper’s abstract and their kindly provided background materials.

It is considered worse-than-poor-form to show how a magic trick is done, either before or after it is performed. But in this case I must – it is the point of this essay.

C&W state explicitly above “This highlights the danger of drawing conclusions from trends calculated over short periods.” Well, of course it does. In the world of performing magic, in the old style, patter, the words spoken by the performer, supplied a great deal of the distraction and misdirection required to make the magic acts work. This bit, used by C&W, is “the denial” — in which the performer formally and explicitly denies that he is going to do something to trick the audience, even at the very moment that he does that exact thing.

If I were performing a similar trick, as a stage magician, you would have heard me say something along the lines of

“Dear friends, you all know that the acts of magic I perform are all tricks – many of you don’t really believe in Magic. You may think I’ll attempt to distract you while fooling you in some way. Rest assured, this is not so….I invite you to watch closely my every move. You may find there is magic after all. Look, there is nothing up my sleeve, nothing in my hat. [Carefully exaggeratedly displaying sleeve and hat] Now, look at this beautiful silk scarf [magician spreads it for all to see, then tosses the three foot square of brilliant red silk high into the air, following with his eyes]. Nothing in there either.”

Note: The manual for this card trick calls for the Magician to switch the deck of cards that has been previously inspected by the dupe, by this method: While displaying the scarf, the magician sweeps the inspected deck of cards into the hidden black well built into the table with the left hand and dropping in its place a new deck, palmed from wherever is convenient. All of this while pointing at the red scarf with the right hand, following the path of the flying scarf with his eyes and an exaggerated tilt of his head. The new deck, of course, contains cards in the carefully pre-arranged order required by the magician for the trick at hand.

Some magicians call this move “the follow”, others simply “the distraction”. The audience’s eyes will follow the scarf, look where the magician points, and look where he looks. I have never had even the most skeptical audience (not even ‘tweenage boys) catch me at this.

Having read a half-dozen or more blog posts on C&W 2013, and hoping to understand it better, I followed links to their Background materials. The instant I saw the graph above, I exclaimed out loud to my wife “Look, they’ve used the old ‘Look at the red scarf’ trick!” (I repeat, I have no information or opinion on whether or not they have done this intentionally.)

Here’s the graphic without the “red scarves”:

Now what do you see?

What we don’t see is what C&W claim: “Temperature data from the Met Office (thin lines) compared to the optimal Cowtan and Way (2013) global reconstruction (thick lines). The straight red lines indicate the trend over the past 16 years in the respective data.”

Quite honestly, you don’t see such a trend or differences in such trends because there is no reason to look at this graph in that particular way and their claim honestly is not clearly demonstrated by their graphic or their work. The two trend lines are the red scarves. Both trend lines are the same trick, in reality, but for their desired effect, the one they want you to focus on is thicker and bolder, to highlight the difference in slope over 16 years. Yet, their whole work is a new calculation of global temperatures using their new technique for evaluating missing data points in spatial coverage of the Arctic, over a 33 year period. They have caused you too look at the red scarves (supplied trend lines) and not the whole graphically presented data set.

And, that, my friends, is the trick using The Red Scarf Follow, C&W got us to see something that without the trick, we would not have seen at all and to not see the rest of what they have done.

[That’s it, Magic Fans….the rest is a bit of commentary on what shows in the graph without the red scarves.]

Here’s what I see in their findings, you may see something different:

[***Image modified 26 Nov 2013 adding in starred blue box: h/t comment from Bill_W ]

From 1979 to around 2005 or 2006, the new technique does not produce anything different than what we already had. Sometimes their data is a few hundredths of a degree higher, sometimes a few hundredths of a degree lower. If it had been any closer a match, I, for one, would have called foul….it would have been suspicious that a major change in the method would produce exactly the same results. There are no signs of a long-term bias—warm or cool—in the Met Office data compared to their new Global.

In 2005, 2006, and the first part of 2007 there seems to be some discernible differences, still in the one or two hundredths of a degree range, which disappear for a year or more beginning what looks like mid-2007 and lasts until 2009 (the right edge of the yellow box). There is something definitely different in the last few years of the data.

What that difference is, I don’t know, nor do I have any idea why it is different and only in those last few years……but it seems highly unlikely to me that a long-standing cool-biasing methodological error (regarding infilling or not of Arctic data) at the MET OFFICE becomes visible only in the last few years of a 33 year data set.

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Moderation Note: This is not a technical thread, and has almost nothing to do with Global Warming, Climate Change, or Arctic temperatures, in-filled, ‘kriged’ or not. It is simply an observation and follows from my recent essays on trends in general. I will follow comments and answer questions on amateur magicianship but not on climate issues. I would like to see your thoughts on what you see in the graph, sans trend lines.

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*** Addendum (26 Nov 2013): Moved up from comment by Bill_W: “There should be another box around the 1998-2001 region [added in blue in image above – kh]. There the new data is lower while in the more recent data it is higher. So the slope changes due to changes at each end in the 16 year time frame. The 16 year period also starts around the year 1998. This is ironic given how often that argument has been used to minimize the pause.” My reply was “Very perceptive ==> That is a good point and I did miss it. Their finding a ‘Met Office warm bias’ in the 1998-2002 period brings the [left]-hand side of their bold trend line down, increasing the slope to the raised ‘Met Office cool biased’ end years.” The combination of the two creates the oft-seen Climate Science graphical “trick” == The Pivot == cool the past and warm the present to make a rising temperature trend. ***

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