Monday, November 30, 2009

DIY - Very Simple "Hockey Stick"

A while back, when I analyzed raw data from Mann & Jones (2003), I came up with my own "hockey stick" graph. I didn't post it then, but I thought it might be interesting now, in light of the CRU incident.

AGW "skeptics" are pushing the idea that Phil Jones' "trick to hide the decline", and the VERY ARTIFICIAL correction I discussed in a prior post are essentially evidence of tampering with the "hockey stick" reconstruction.

In reality, the artificial correction refers to rudimentary, probably temporary code (apparently marked with all-caps comments to caution CRU researchers not to use it as final code) that corrects temperatures derived from tree-ring widths, due to a problem known as "tree-ring divergence." It's highly improbable the artificial correction was ever used in any published paper.



This "hockey stick" does not require you to write any algorithms. The only "tricks" involved in producing it are the following:

  1. Temperature data up to 1980 comes from Mann & Jones (2003) (data made available by NOAA.)
  2. Temperature from 1981 onwards comes from the CRUTEM3v global data set.
  3. The red line is a 25-year central moving average of the temperature series.


You can try this yourself with different data sets. It's not very difficult. If you don't trust CRU temperature data, use GISSTemp. If you don't think the Mann & Jones (2003) reconstruction should be used, there are plenty of other historical reconstructions that use methods other than tree-rings. Do report back if it doesn't work. Comment moderation is never enabled here.

[Errata 11/30/2009: The post initially said the red line was a 75-year central moving average. It's actually a 25-year CMA.]

21 comments:

Sully said...

Does this mean I should buy beachfront property on the Artic Ocean coast of Canada? Naturally I would look for a property with some depth on a rising slope.

Joseph said...

It simply means current warming is unprecedented for at least 1800 years.

Anonymous said...

Joseph,

Would you describe what you did as grafting an instrumental temperature data record onto a proxy reconstruction?

John M

Joseph said...

@John: That's a correct characterization.

Anonymous said...

Joseph,

Thanks for the response. I wanted to make sure that's what you would call it, since Michael Mann, when discussing a claim that he had done just that with what we now know is his "trick", had this to say:

"No researchers in this field have ever, to our knowledge, "grafted the thermometer record onto" any reconstruction. It is somewhat disappointing to find this specious claim (which we usually find originating from industry-funded climate disinformation websites) appearing in this forum."

http://www.realclimate.org/index.php?p=11#comments

John M

Joseph said...

But he goes on to state:

Most proxy reconstructions end somewhere around 1980, for the reasons discussed above. Often, as in the comparisons we show on this site, the instrumental record (which extends to present) is shown along with the reconstructions, and clearly distinguished from them (e.g. highlighted in red as here)

I think that's clear enough. He doesn't consider it grafting because the different series are clearly marked. I've seen the graphs that appear in the published papers. They are.

Anonymous said...

Sorry, Joseph, words have meaning.

From my quote:

"No researchers in this field have ever, to our knowledge..."

From your quote

"Often, as in the comparisons we show on this site..."

Note the difference between "no researchers...have ever" and "often". I've learned one has to read RealClimate RealCareful.

The proxy data was indeed removed and replaced with instrumental data in papers in the late 90s and even in the 2001 IPCC, just as you did. Perhaps Mann decided that "often" was good enough for the argument he was making in 2005, but in 1998, which is the time-frame of the "trick" email, it is clear that "grafted" curves were being used.

http://www.climateaudit.org/?p=7844

But that's OK, you're not the first Mann defender that happily claimed that "grafting" was perfectly acceptable until the Mann quote was pointed out to him. It seems that even Gerry North had to correct himself.

http://camirror.wordpress.com/2009/12/01/gerry-north-doesnt-understand-the-trick/#comments

John M

Joseph said...

@John: Can you show me the specific graph?

I was just looking at this review, and indeed you'll see that the instrumental record appears in black (it stands out from reconstructions) and there's a legend for it.

Either way, this all sounds like nitpicking. The limitations of the procedure are what they are regardless of whether you call it "trick" or "grafting."

Anonymous said...

Joseph,

I believe your figure is from the 4th IPCC report. The "original" hockey stick was shown in the 3rd, and was based on the "trick".

It is shown and discussed here.

http://camirror.wordpress.com/2009/11/26/the-trick/#more-62

The proxy data at the end of the record was removed and replaced with instrumental data.

Perhaps you think it's picky to point out that Michael Mann did something he later called "a specious claim", and to point out that he still appears to be denying it.

I don't.

John M

Joseph said...

That graph also has the instrumental series labeled with a legend. The reconstructed series stop at what appears to be 1980, and there's nothing unusual about that.

I'm not sure I'd call it a specious claim. He has an opinion on what it means to "graft" a series onto another. The concept seems subjective to me, and the discussion as to what it should be called not very interesting.

Anonymous said...

All depends on what your definition of the word "is" is.

kunzang said...

The trick was meant to mislead. So is calling it the "divergence problem." In other fields one would say the tree's are not correlated with the temperature record after 1960. This is problematic because it adds uncertainty to historical reconstruction.

Joseph said...

@kunzang: Show me the published graph where the "trick" described in the emails was applied.

Anonymous said...

The actual graph to which the emails refer using the "trick" is on the first page of this 1999 report.

http://www.wmo.ch/pages/prog/wcp/wcdmp/statemnt/wmo913.pdf

The graphs are a result of truncating/combining/smoothing proxy data with the instrumental temperature record. The original, untruncated/uncombined graphs are here.

http://www.uea.ac.uk/polopoly_fs/1.138393!imageManager/4052145227.jpg

Note: the part of the proxy that was kept was actually blended and smoothed together with the tempeature record, thus making the splice/graft look smooth and uniform, as if it was one temperature record. It was not merely truncating the "bad" proxy data and continuing on with the "good" instrumental data, and it certainly wasn't overlaying all data.

The "trick" is referred to as "Mike's Nature trick" because Mann purportedly used it in a 1998 Nature paper.

Anonymous said...

The above comment was me.

John M

Anonymous said...

Oh hell, that first link should be:

http://www.wmo.ch/pages/prog/wcp/wcdmp/statemnt/wmo913.pdf

If this still doesn't work, google: jones climate wmo 1999

Should be the first hit.

Joseph said...

Right. The "trick" is simply to add the real temps from 1981 onwards, and from 1961 onwards to Keith Briffa's (tree-ring reconstruction) in order to "hide the decline" that was clearly explained in Briffa et al. (1998).

I was confusing the "trick" with the "very artificial correction" which is somewhat related, but not the same thing.

Anonymous said...

Joseph,

No, they weren't merely "added". The proxy data was "truncated", the two data sets (minus the truncated portion) were "merged" or "grafted", and "smoothed" together, and presented as one data set.

Mixing two types of data from two significantly differing techniques with vastly differing uncertainties and errors, eliminating the "bad" portion, and showing them as one is, at a minimum, misleading.

Once again, that is why Mann went out of his way to say:

"No researchers in this field have ever, to our knowledge, "grafted the thermometer record onto" any reconstruction. It is somewhat disappointing to find this specious claim (which we usually find originating from industry-funded climate disinformation websites) appearing in this forum."

It is quite amusing now seeing so many people saying "problem, what problem?"

John M

MartinM said...

The actual graph to which the emails refer using the "trick" is on the first page of this 1999 report.

Well, let's look at this in more detail, then. The green line on that graph comes from this paper. Take a look at the last panel of Figure 1; the Northern chronology average. Looks a lot like the WMO curve, and not particularly like the alleged 'untruncated' one. I think you'll find the discrepancy between the two is simply because the 'untruncated' version is, in fact, truncated. The green line clearly stops at around 1960, whereas both WMO and the Briffa paper go right up to 1999.

I don't have access to the Mann or Jones papers; perhaps someone else can take a look at those ones. But the Briffa series hasn't been 'tricked' at all, as far as I can tell.

Anonymous said...

MartinM,

Do you agree that the instrumental data was spliced onto the proxy data?

John M

MartinM said...

It may have been. I'm not convinced of that for the Briffa series, for reasons already given. I haven't seen the papers the other two derive from.