Wednesday, March 03, 2010

Stephen McIntyre makes false claim to committee, invalidates whole AGW skeptic case

Steve McIntyre, one of the main AGW (Man-made climate change) sceptics, has made a submission to the UK Parliament's Science and Technology Committee into the East Anglia University hacked emails. His submission is here.

In para. 7 he refers to tree ring data. This has a close relationship to temperature, except in the later years of a tree's life, when rings are stretched thinner, and therefore produce a false impression of colder climate. Dendrochronologists therefore have to make an adjustment to the data to allow for this fact.

McIntyre however states in his paper, "there was no scientific basis for such an arbitrary adjustment". (para. 8).

I wrote a polite question on his blog discussion thread asking him about this point.

Posted Feb 28, 2010 at 1:38 PM | Permalink | Reply
Steve, you say “there was no scientific basis for such an arbitrary adjustment” [of the tree ring record], my understanding is that it is a feature of dendrochronology that more recently laid down tree rings are thinner than those buried more deeply within the tree. Which would create a scientific basis for applying an adjustment. Would it not?

Steve: Not this adjustment.

  • MrPete
    Posted Feb 28, 2010 at 7:54 PM | Permalink | Reply
    Re: Richard Lawson (Feb 28 13:38),
    That’s not an arbitrary adjustment. Carefully-constructed mathematical methods, with some physical principles underlying, take care of the general time-related growth changes. Even those engender much discussion. But at least they aren’t completely arbitrary.

So it seems that McIntyre is wrong about tree rings. The charitable interpretation is that he does not understand. But he should do, because he has been banging on about it for years and years.

Now, then, let's get into Daily Express mode: [CAUTION: IRONY WARNING!!]

Canadian engineer Steve McIntyre, the self-styled "scientist" at the heart of the vicious attack on the future of the planet, has an error of science right at the heart  of his submission to respected Science and Technology Parliamentary Committee. He does not understand the basic facts of tree ring data. This latest revelation totally invalidates the case of climate skeptics, and proves that ...


Sorry, I can't keep it up.  But this is indeed a cameo of what is happening.  The sceptics take a single error, inflate it into a general refutation of the whole picture, weak-minded and gullible journalists take it up, and the grasp of the public on what is going on is further diminished.
Goebbles must be giggling in his grave.

Here is a detailed answer to McIntyre by Briffa on this question.


StuartM said...

Richard, Like this one, makes a good point in an amusing (but also terrifying) way.

Anonymous said...

Dear Doc,
As I understand it, nobody knows why there is a divergence in the tree-ring proxies:-

“During the second half of the twentieth century, the decadal-scale trends in wood density and summer temperatures have increasingly diverged as wood density has progressively fallen. The cause of this increasing insensitivity of wood density to temperature changes is not known, but if it is not taken into account in dendroclimatic reconstructions, past temperatures could be overestimated… In the areas where the growth data extend through to the warm late 1980s and early 1990s (NEUR, WSIB, CSIB, ESIB), the divergence is at a maximum in the most recent years. Over the hemisphere, the divergence between tree growth and mean summer temperatures began perhaps as early as the 1930s; became clearly recognisable, particularly in the north, after 1960; and has continued to increase up until the end of the common record at around 1990.”
Briffa et al [Nature 391 1998]

“The causes (of the divergence problem), however are not well understood and are difficult to test due to the existence of a number of co-varying environmental factors that may potentially impact recent tree growth.”
D’Arrigo et al. 2007

Briffa’s big worry was that the decline could cause prior reconstructions to have high values, arguing that the late decline should be excluded in calibration. They seemingly ignoring the elephant in the room: whether these proxies can pick up warm climates at all.

The “divergence problem” has been discussed on many occasions at this site. If ring widths have gone down in the last half of the 20th century despite increasing temperatures, how can we use information from prior periods to reconstruct past temperatures? Kurt Cuffey was much puzzled by this conundrum at the NAS panel hearings.

Your statement:-

“This has a close relationship to temperature, except in the later years of a tree's life, when rings are stretched thinner, and therefore produce a false impression of colder climate. Dendrochronologists therefore have to make an adjustment to the data to allow for this fact.”

seems to assume that this is a well-understood and unproblematic phenomenon, but it is not understood. And if you don’t know why something is happening then you don’t have a “scientific” basis for adjusting it.

Also, why change the end of the graph by substituting the instrumental temperature record for the dendro proxy record without saying that that is what you are doing?

I think you may have mistaken McIntyre’s reply-surely he was disagreeing with you? That is my reading of his reply ‘Not this adjustment’.
I am interested in where McIntyre styles himself a scientist?
You are misspelling his name in some places.

DocRichard said...

Hi JMac

Thank you for this astute and helpful comment. You make some good points.

Sure, it could be that past temperatures could have been OVERESTIMATED. In this case, the MWP would also have been overestimated, which takes out of the sails of the "What about the MWP?" question. Doesn't it?

It puzzles me that more recent tree rings would be thinner. I would have expected them to be fatter - new wood full of juice, later to be compressed. I have phoned an arboriculturalist about this. He had no direct knowledge of bristlecone pines, but mentioned that as well as sunlight, other factors affect tree rings size, primarily water availability. He was sure that older rings could not grow in size with time.

The key thing about all of this is that dendrochronology can be completely taken out of the equation without losing the picture. We can get paleotemperature data from many other sources - corals, stalagmites, and ice cores. All come to the same conclusion - current temperatures are higher than for many thousands of years, higher than the MWP. The only plausible explanation that can account for recent temperatures is enhanced greenhouse effect caused by our GHGs.

Thanks again

DocRichard said...

"Also, why change the end of the graph by substituting the instrumental temperature record for the dendro proxy record without saying that that is what you are doing?"

Are your sure that he did not say what he was doing in that paper? This decline is well discussed in the literature. It might well have been footnoted. And, yes, I admit I have not read the original. If you have, and you cannot find it, give me the reference and I will take a look at it. Reluctantly. I would prefer to leave dedrochronology to the dendrochronologists, in view of the fact that we have other proxies that tell the same story.

I will amend the record wrt spelling &c. McIntyre+McKitrick = McKintyre. doh.

DocRichard said...

JMac, the "scientist" thing is protected by the irony caution at the head of this blog.

It is a pastiche of a Daily Express article, as if that rag were to treat an error from a sceptic in the same way that they treat an error by a climate scientist. The error is meant to represent the kind of error that we get in newspapers. I will put up an irony warning.

DocRichard said...

JMac, I had a poke round to see if I could get back to the source. The reference is 20.Briffa K.R.,Jones P.D. et al. Fennoscandian summer from AD 500: temperature changes on short and long timescales."Climate Dynamics", 1992,7:111-119.
McIntyre gave an incomplete reference, I wonder if I could get the Sunday Times interested in that? (See Getting to the source of the "Amazongate" here)

I would have to buy the paper in, all to find out whether and why there is not a scientific reason for that adjustment, as opposed to others. Sorry, life is short.

Anonymous said...

Yes-sorry about the irony business, I didn't read your post as carefully as I should have.

I cut and paste some relevant comment from climateaudit below:-

“Hide the decline” refers to the decline in the Briffa MXD temperature reconstruction in the last half of the 20th century, a decline that called into question the validity of the tree ring reconstructions. –Mcintyre

In the IPCC Third and Fourth Assessment Reports, IPCC “hid the decline” by simply deleting the post-1960 values of the troublesome Briffa reconstruction

Not only were the post-1960 values of the Briffa reconstruction not shown in the IPCC 2001 report … they were deleted from the archived version of the reconstruction at NOAA.

Briffa 2000 (cited in the caption to IPCC Fig 2.21) did show the decline as shown in Briffa 2000 This series obviously goes down at the end .What Gavin didn’t discuss is how you get from the version below to the IPCC version..

There is no mention in the IPCC report of the deletion of Briffa reconstruction data after 1960. Nor is there any mention of the deletion in the IPCC reference (Briffa 2000) nor, for that matter, in the article cited by Gavin Schmidt (Briffa et al 1998).

When smoothing these time series, the Team had a problem: actual reconstructions “diverge” from the instrumental series in the last part of 20th century. In order to smooth those time series one needs to “pad” the series beyond the end time, and no matter what method one uses, this leads to a smoothed graph pointing downwards in the end whereas the smoothed instrumental series is pointing upwards — a divergence. So Mann’s solution was to use the instrumental record for padding, which changes the smoothed series to point upwards.

DocRichard said...

Hi JMac
All the points made confirm that there is a decline. This is a known issue in dendrochronology - tree rings become thinner towards the end of the tree's life, for whatever reason. Before the terminal years, the rings, especially their density, give good proxies for the temperatures. Towards the end of their life, they get thinner - they decline. I may be being thick here, but I cannot see what the problem is. There is an artefact in the data, and it needs to be corrected to bring it into line with observed temperatures. It would be a problem if dendrochronology diverged from other proxies, but it doesn't.

On another matter, McIntyre says that to not correct the decline would lead to past temps to be "overestimated". Surely he means "underestimated"?? If we ignored the decline, and set the temperature to modern ring densities, that would indeed shove the past temp records way up, which is what McIntyre
wants, is it not?
is a good review source, from the New Scientist.

DocRichard said...

It may be warmer now than for the last million years.
That's a lot. Maybe they are out in their calculations. I would accept a reduction of three orders of magnitude, and I would still want to decarbonise...

Anonymous said...

Global warming is a scam.

DocRichard said...

And a scam is a a fraudulent business scheme. Global warming has several causes, and the component that we can affect is our CO2 emissions. The oil companies who produce the emissions have spent the last 30 years fraudulently challenging the facts using cod "science". First they claimed that warming was not happening, now when it is undeniable that it is happening, they are fraudulently trying to take the blame away from their product. Yes, that is a scam.