Dr. Judith Curry is entering the fray about tree ring proxies and the problems associated with their usage in the IPCC.
Hiding the Decline
by Judith Curry
To date, I’ve kept Climate Etc. a “tree ring free zone,” since the issues surrounding the hockey stick are a black hole for conflict and pretty much a tar baby, IMO. Further, paleoproxies are outside the arena of my personal research expertise, and I find my eyes glaze over when I start reading about bristlecones, etc. However, two things this week have changed my mind, and I have decided to take on one aspect of this issue: the infamous “hide the decline.”
The first thing that contributed to my mind change was this post at Bishop Hill entitled “Will Sir John condemn hide the decline?”, related to Sir John Beddington’s statement: It is time the scientific community became proactive in challenging misuse of scientific evidence.
The second thing was this youtube clip of physicist Richard Muller (Director of the Berkeley Earth Project), where he discusses “hide the decline” and vehemently refers to this as “dishonest,” and says “you are not allowed to do this,” and further states that he intends not to read further papers by these authors (note “hide the decline” appears around minute 31 into the clip). While most of his research is in physics, Muller has also published important papers on paleoclimate, including a controversial paper that supported McIntyre and McKitrick’s analysis.
The question I am asking myself is what is my role as a scientist in challenging misuses of science (as per Beddington’s challenge)? Why or why not should I personally get involved in this? Is hiding the decline dishonest and/or bad science?
Explanations, interpretations, and misrepresentations of “hide the decline”
Realclimate describes the issue as follows:
Phil Jones in discussing the presentation of temperature reconstructions stated that “I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith’s to hide the decline.” The paper in question is the Mann, Bradley and Hughes (1998) Nature paper on the original multiproxy temperature reconstruction, and the ‘trick’ is just to plot the instrumental records along with reconstruction so that the context of the recent warming is clear. Scientists often use the term “trick” to refer to a “a good way to deal with a problem”, rather than something that is “secret”, and so there is nothing problematic in this at all. As for the ‘decline’, it is well known that Keith Briffa’s maximum latewood tree ring density proxy diverges from the temperature records after 1960 (this is more commonly known as the “divergence problem”–see e.g. the recent discussion in this paper) and has been discussed in the literature since Briffa et al in Nature in 1998 (Nature, 391, 678-682). Those authors have always recommend not using the post 1960 part of their reconstruction, and so while ‘hiding’ is probably a poor choice of words (since it is ‘hidden’ in plain sight), not using the data in the plot is completely appropriate, as is further research to understand why this happens.
Steve McIntyre has quite a different intepretation. With regards to Briffa 1998:
Despite relatively little centennial variability, Briffa’s reconstruction had a noticeable decline in the late 20th century, despite warmer temperatures. In these early articles [e.g. Briffa 1998], the decline was not hidden.
For most analysts, the seemingly unavoidable question at this point would be – if tree rings didn’t respond to late 20th century warmth, how would one know that they didn’t do the same thing in response to possible medieval warmth – a question that remains unaddressed years later.
Briffa et al 1998a (Nature 391): 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.
With regards to the IPCC TAR:
In a post-mortem a few weeks later, Coordinating Lead Author Folland wrote that, although a proxy diagram was “a clear favourite for the Policy Makers summary”, the Briffa reconstruction “dilutes the message rather significantly”, adding that this was “probably the most important issue to resolve in Chapter 2 at present”. Mann wrote that “everyone in the room” agreed that the Briffa series was a “potential distraction/detraction from the reasonably consensus viewpoint we’d like to show”. Briffa recognized there was “pressure to present a nice tidy story as regards ‘apparent unprecedented warming in a thousand years or more ’”, but expressed many caveats, in particular that the proxies were not responding the way that they were supposed to and that that the recent warmth was “probably matched” 1000 years ago.
Otherwise, the skeptics have an field day casting doubt on our ability to understand the factors that influence these estimates and, thus, can undermine faith in the paleoestimates. I don’t think that doubt is scientifically justified, and I’d hate to be the one to have to give it fodder! (Mann Sep 22, 0938018124.txt)
And on and on, McIntyre provides substantial documentation for his analysis.
With this context, the media has continued to completely misrepresent the situation, being inconsistent with either the RC or McIntyre analyses. Tim Lambert provides a summary of recent inaccurate media statements, here is a common example:
4 February 2011, Investor’s Business Daily: The ClimateGate scandal was a direct result of scientists — and we use the term loosely — at Britain’s Climate Research Unit and others, such as Michael Mann, conspiring to manipulate data to “hide the decline” in global temperatures.
The obvious inaccuracy of such statements and their easy refutation distracts from addressing the substantive issues raised by McIntyre.
Bad science and/or dishonesty?
There is no question that the diagrams and accompanying text in the IPCC TAR, AR4 and WMO 1999 are misleading. I was misled. Upon considering the material presented in these reports, it did not occur to me that recent paleo data was not consistent with the historical record. The one statement in AR4 (put in after McIntyre’s insistence as a reviewer) that mentions the divergence problem is weak tea.
It is obvious that there has been deletion of adverse data in figures shown IPCC AR3 and AR4, and the 1999 WMO document. Not only is this misleading, but it is dishonest (I agree with Muller on this one). The authors defend themselves by stating that there has been no attempt to hide the divergence problem in the literature, and that the relevant paper was referenced. I infer then that there is something in the IPCC process or the authors’ interpretation of the IPCC process (i.e. don’t dilute the message) that corrupted the scientists into deleting the adverse data in these diagrams.
McIntyre’s analysis is sufficiently well documented that it is difficult to imagine that his analysis is incorrect in any significant way. If his analysis is incorrect, it should be refuted. I would like to know what the heck Mann, Briffa, Jones et al. were thinking when they did this and why they did this, and how they can defend this, although the emails provide pretty strong clues. Does the IPCC regard this as acceptable? I sure don’t.
Can anyone defend “hide the decline”? I would much prefer to be wrong in my interpretation, but I fear that I am not.
State of the paleoreconstruction science
This raises the issue as to whether there is any value at all in the tree ring analyses for this application, and whether these paleoreconstructions can tell us anything. Apart from the issue of the proxies not matching the observations from the current period of warming (which is also the period of best historical data), there is the further issue as to whether these hemispheric or global temperature analyses make any sense at all because of the sampling issue. I am personally having a difficult time in seeing how this stuff has any credibility at the level of “likely” confidence levels reported in the TAR and AR4.
I am really hoping that the AR5 will do a better job of providing a useful analysis and assessment of the paleodata for the last millennium. However I am not too optimistic. There was another Workshop in Lisbon this past year (Sept 2010), on the Medieval Warm Period. The abstracts for the presentations are found here. No surprises, many of the usual people doing the usual things.
I view paleoclimate as a really important subject in the context of understanding climate change. I have no interest in warmest year or warmest decade; rather we need to understand the magnitude and characteristics and causes of natural climate variability over the current interglacial, particularly the last 2000 years. I’m more interested in the handle than the blade of the hockey stick. I also view understanding regional climate variations as much more important than trying to use some statistical model to create global average anomalies (which I personally regard as pointless, given the sampling issue).
I don’t want to throw the baby away with the bath water here. But this whole issue is a big problem for the science and has been an enormous black eye for the credibility of the IPCC and climate science. I suspect that many denizens will be on board with my assessment and are very familiar with McIntyre’s analysis. I would be particularly interested in hearing from any defenders of these global paleotemperature analyses by Mann et al.
If there is a problem, lets get to the bottom of it and fix it.