Trenberth on Statistics

Jan 5, 2006 – 9:26 AM

I don’t think that people entirely appreciate the absurdity of the views of Gavin and Rasmus that consideration of persistence in climate somehow "pitches statistics against physics". If climate scientists are seeking more familiar authority for just how preposterous this claim is, they need look no further than Trenberth [1984], previously discussed on this blog here, which categorically asserts that many statistics will be seriously biased by autocorrelation. The forms of persistence discussed by Trenberth are less severe than the ones considered by Cohn and Lins and Koutsoyannis, but the persistence issue then becomes a matter of degree (rather than of "physics").

Here is an extended excerpt from Trenberth:

Climate is usually regarded as dealing with the average behavior over a relatively long time of the climate system and is not concerned with the daily fluctuations called weather… The focus of many climate studies is the difference between any climatic states that can be distinguished from the climatic noise. This “climatic signal” may arise from influences truly external to the climate system or it may arise from slowly varying modes of the entire climate system…Two other aspects are also important in time series analysis of meteorological parameters…(2) persistence, which gives rise to a lack of independence in the observations. Leith (1973, 1975) discussed the problem of signal-noise ratio in the predictability of climate and showed that the magnitude of the noise was related to persistence in the atmosphere…

However this climatic noise and the persistence, along with the finite size of the samples must be taken into consideration when computing statistics of the circulation or the resulting statistics may be significantly biased…

Trenberth pointed out that”many publications have failed to take note of the potential problems” and goes on to point out severe biases in the estimation of variances, covariances and autocorrelations. He concluded as follows:

“This paper has pointed out the need to take persistence into account in estimating population statistics from a finite sample”.

It’s pretty hard to see a more on-point and more categorical refutation of realclimate’s view of the statistical issues involved with persistence. I’ll probably leave these matters alone for a while, but will conclude by pointing out the following from the Climate Analysis Group, University of Reading:

Climate by definition is the statistics of weather. It therefore makes a lot of sense that climate researchers know something about the important subject of statistics.

It’s too bad that so many climate scientists, who hold themselves out as authorities, actually have such sketchy knowledge of statistics and that, despite this, have generally failed to involve statistical professionals in their work.

By the way, the University of Reading group has some interesting-looking (I haven’t inspected the packages) information on specialized R packages here and here .

Reference: Trenberth, K. [1984], Some effects of finite sample size and persistence on meteorological statistics. Part I: Autocorrelation. Monthly Weather Review, 112, 2359-2368

By Stephen McIntyre | Posted in Statistics | Tagged | Comments (38)

Demetris Koutsoyannis

Jan 5, 2006 – 8:50 AM

I mentioned a few days ago that a serious discussion had threatened to break out at realclimate, where Demetris Koutsoyannis had posted up some astute commentary. He has recently dropped in here as well. I was unfamiliar with his work prior to this recent introduction. He has written extensively on climate, much of which has been from a statistical viewpoint much more advanced than poor old Rasmus.I began writing a commentary on his realclimate post, but instead have simply reproduced it below as it deserves to be read in its entirety, following some short introductory comments. Continue reading →

By Stephen McIntyre | Posted in Statistics | Tagged , | Comments (83)

To Browsing Undergraduates

Jan 5, 2006 – 6:52 AM

Our "blogfather", realclimate, has been celebrating their one-year anniversary (congratulations to them) and have been reflecting on their year. Kenneth Blumenfeld, who’s posted here once or twice, posted an interesting comment at realclimate, about how his undergraduates were now investigating climate change issues online, that they "very badly wanted to get behind RC", but wanted them to "step up to the plate, not just take practice swings", mentioning that they were getting their butts kicked. To any such undergraduates that may have come to this site: welcome. Continue reading →

By Stephen McIntyre | Posted in General | Comments (240)

Another Quandary for Sciencemag

Jan 4, 2006 – 2:32 PM

A few days ago, Science retracted the 2005 Hwang paper. But it turns out that the retraction was wrong, since the retraction left 2 lines pending. Now Science is trying to figure out how to re-retract the paper. You’d think that they could have got the retraction right. Update Jan. 8, 2006: It appears that they did not get to retracting it after all, and it is still unretracted pending finalization of retraction language.

The New York Times describes the comedy as follows:

There is no question in our minds that the stem cell paper published 19 May 2005 by the journal Science needs to be retracted," wrote Donald Kennedy, the journal’s editor in a statement released Thursday. He added that Science asked all 25 authors to sign a retraction and said that if the journal did not receive all the signatures by Friday, it would prepare to retract the paper on its own. By yesterday, said a Science spokeswoman, Ginger Pinholster, all but one had signed.

Then a new problem arose: The retraction did not include information revealed in South Korea at a news conference on Thursday. Until then, it had seemed possible that Dr. Hwang’s group had created 2 cloned stem cell lines, not 11. On Thursday, the investigators in Seoul said that even those two were not clones. Science sought confirmation of the news reports from Roe Jung Hye, dean of research affairs, and got it. That means, Dr. Kelner said, that "the wording of the retraction is not correct." Now the staff needs to meet to discuss how to proceed, she said, because "once a paper is retracted, you can’t retract it again."

By Stephen McIntyre | Posted in Disclosure and Diligence | Comments (4)

Cutting Down the Oldest Living Tree in the World

Jan 3, 2006 – 9:16 AM

Many Americans of a certain age will recall an American radio commentator, called Paul Harvey, who ran ironic commentaries entitled "The End of the Story". They were short segments leading you to expect one answer and Harvey’s closing comment explaining what happened would reverse the field altogether. I once heard a commentary on dendrochronology, in which Harvey reported how a dendrochronologist had cut down and killed the oldest living tree in the world. In my pre-blog days, when I was researching bristlecones, I came across the academic account of this event – which I summarize here. Continue reading →

By Stephen McIntyre | Posted in bristlecones | Comments (36)

A realclimate Advisory

Jan 2, 2006 – 9:47 AM

Warning – a serious discussion has unexpectedly broken out at realclimate. See comments 84 and 85 here. I don’t think that the IID team is faring very well.

By Stephen McIntyre | Posted in General | Comments (56)

Upper and Lower Bristlecone Sites

Jan 1, 2006 – 11:29 AM

A while ago, I discussed the very interesting study by Naurzbaev et al [2004] (co-author Hughes), which calculated growth curves at 34 larch sites in a meridional transect from 55 to 72 N (at a longitude of about 90-100E) and 23 larch sites along an altitudinal transect from 1120 to 2350 m around Tuva (~ 51N, 95E). This appeared to me to be a nicely systematic approach to trying to extract climatic information from tree rings, as opposed to Mann’s peculiar data mining methods. They calculated growth curves by age for various sites and asserted that the parameters were related to latitude and elevation. This represented the simple point that ring widths at higher latitudes/elevations were thinner than for lower latitudes/elevations – which is the premise of using ring widths as a temperature proxy.

Hughes and Funkhouser [Climatic Change, 2003] studied 4 bristlecone/foxtail paired sites at upper and lower elevations. The elevation differences ranges from 200 meters (Timber Gap) to 600 meters (White Mountains). I thought that it would be interesting to do some simple comparisons of ring widths at these paired sites. In order to use bristlecone ring widths directly as a temperature proxy, one would presume that the ring widths at the (cooler) higher sites would be narrower than the ring widths at the (warmer) lower sites. Continue reading →

By Stephen McIntyre | Posted in bristlecones, Proxies | Tagged , , , , , | Comments (18)

Kennedy, Editor of Science, on PBS

Dec 28, 2005 – 10:27 AM

There is an interesting discussion at PBS on peer review, in which Donald Kennedy, editor of Science, defended their existing "rigorous" processes, but re-iterated:

the journal has to trust its reviewers; it has to trust the source. It can’t go in and demand the data books.

If I criticize Science’s due diligence procedures, I don’t think that anyone will accuse me of piling on after the Hwang affair. Here’s something that I wrote last summer:

the underlying issue is that Science does not seem to either have policies that require authors to archive data or administration practices that ensure that their policies are applied. Since NSF then relies ( a reliance which seems to me to be an abdication of their own separate responsibilities) on journals like Science, with either inadequate policy or inadequate administration, there’s a knock-on effect.

Here are some comments on the PBS interview and some re-cap of past commentary. Continue reading →

By Stephen McIntyre | Posted in Disclosure and Diligence | Tagged | Comments (100)

The Hwang Affair: A Chronology

Dec 27, 2005 – 8:46 AM

I’ve planning to discuss Nature and Science policies on archiving and due diligence, I’ve got lots else to do, but have gotten sidetracked in the fascinating details of the unfolding of the Hwang controversy. Here’s a preliminary account. Continue reading →

By Stephen McIntyre | Posted in Disclosure and Diligence | Tagged , | Comments (18)

Washington Post: Stem Cell Debacle Spurs Calls for Improved Oversight

Dec 26, 2005 – 1:22 PM

Lots of people have criticized me for the mere idea of auditing scientific articles. Think of the many blog-posters who have ridiculed this as a total waste of time for scientists, who should be getting on with more "productive" work. Here’s an endorsement for the concept reported in yesterday’s Washington Post. Continue reading →

By Stephen McIntyre | Posted in Disclosure and Diligence | Comments (23)