The long-awaited (and long overdue) PAGES2K synthesis of 57 high-resolution ocean sediment series (OCEAN2K) was published a couple of weeks ago (see here here). Co-author Michael Evans’ announcement made the results sound like the latest and perhaps most dramatic Hockey Stick yet:

Today, the Earth is warming about 20 times faster than it cooled during the past 1,800 years,” said Michael Evans, second author of the study and an associate professor in the University of Maryland’s Department of Geology and Earth System Science Interdisciplinary Center (ESSIC). “This study truly highlights the profound effects we are having on our climate today.”

A couple of news outlets announced its release with headlines like “1,800 years of global ocean cooling halted by global warming”, but the the event passed unnoticed at realclimate and the newest “Hockey Stick” was somehow omitted from David Appell’s list of bladed objects.

The OCEAN2K Reconstruction

One of the reasons for the strange lack of interest in this newest proxy “Hockey Stick” was that the proxy data didn’t actually show “the climate was warming about 20 times faster than it cooled during the past 1,800 years”. The OCEAN2K reconstruction (see Figure 1 below) had a shape that even David Appell would be hard-pressed to describe as a “Hockey Stick”. It showed a small decrease over the past two millennia with the most recent value having a tiny uptick from its predecessor, but, whatever image one might choose to describe its shape, “Hockey Stick” is not one of them.

FAQ Figure 1: Results of the global sea surface temperature compilation from Ocean2k: A cooling over the past two millenium was reversed only in the most recent two centuries. Fifty-seven previously published and publicly available marine sea surface temperature reconstructions were combined and compiled into 200-year brackets, represented by the boxes. The thin horizontal lines dividing each box are the median of the values in that box. The thick blue line is the median of these values weighted for differences in the region of the global ocean in which they were found. (More in Figure 2a in the paper and Supplementary Table S13. ) Link

Technical Comments

The authors have done a really commendable job of archiving their data as used, the original locations of digital data and have even archived (much of) the code for their reconstruction.

As you can see from the above diagram, the authors have “binned” the data into 200-year bins – a decision which makes the results rather uninformative on the relation of modern proxy values to proxy values earlier in the millennium. While series with high-resolution through the 20th century are not as common as one would like or expect, there are some (I keep an eye out for them and have written at CA about such series from time to time). Given the seeming purpose of the study, its silence on this topic is more than a little surprising. It also seems improbable that their ex ante strategy was to use 200-year bins, given their uninformativeness on modern-historical comparisons. This has the hallmarks of a “researcher degree of freedom” (in Wagenmakers’ sense) – or more colloquially, data torture. I presume that they must have done a study using much higher-resolution bins: I’ve done my own calculations with 20-year bins and will report on them in a later post.

Second, their money graphic is denominated in SD Units, rather than deg C anomaly, even though all of the 57 series in their database (alkenone, Mg/Ca, foraminifera) are denominated in deg C. This seems to me (and is) a pointless degradation of the data that ought to be avoided. Particularly when they want to be able to express the decline in deg C (as they do in a later table.) To do so, they convert their composite back from SD Units to deg C (anomaly) using a complicated home-made technique. I think that there’s an easy way of accomplishing what they want to do using conventional statistical techniques. I’ll show this in a subsequent post.

In addition to the publication of their paleoclimate series, the article includes a lengthy section on simulation of ocean SSTs using climate models with volcanic forcing. While the model simulations are an interesting topic, it is not the expertise of the people collecting the ocean sediment data and requires different contributors. In my opinion, the publication of a composite of 57 ocean sediment series is itself a large enough and meritorious enterprise to warrant publication on its own and ought to have been done separately (and much more promptly, as discussed below).

David Appell’s Cherrypick

David Appell recently listed 36 supposed “hockey sticks” (though many of these supposed “hockey sticks” had pronounced medieval periods and, in my opinion, were more similar to the variations that Ross and I showed a decade ago. One of his series (Spielhagen et al 2011) is among the OCEAN2K proxies, shown in their original in the next figure (SI Figure 1). In accordance with the overall non-HSness of the composite, individual HS’s are hard to spot, but there is one. See if you can spot it before looking at the answer.

Figure 2. From OCEAN2K Figure S1a. The 57 SST series.

In the next figure, I’ve highlighted the Spielhagen 2011 series listed as one of Appell’s hockey sticks. Only one of the 57 series has a noticeable HS-shape and, by coincidence, no doubt, it is the only SST series from this collection that was cited by Appell.

Figure 3. From OCEAN2K Figure S1a. The 57 SST series with the Spielhagen series highlighted.

Among the series that I’ve discussed in the past is lead author McGregor’s offshore Morocco series, which goes down in the 20th century as shown in the highlighted version (solid black) below:

When McGregor originally published this series with decreasing SST, she was able to find a cloud in the silver lining, worrying that increasing strength of “offshore currents may be too strong for fish to swim against”, raising the spectre that scarce resources would have to be diverted to providing swimming lessons to impacted fish. The decrease in SST also had a serious negative impact on multiproxy authors seeking to display hockey sticks. Needless to say, the resourceful authors of Trouet et al 2009 mitigated this adverse impact by turning the data upside down – Cape Ghir below (see here)



The Delay

Another curiosity of the present study is its lengthy delay. The OCEAN2K program had been announced in November 2011, stating their intent to synthesize ocean data in time for AR5 as follows:

We plan to generate two outputs in time for consideration in the IPCC’s Working Group I Fifth assessment report, and contributing to the PAGES2K synthesis planned for 2014. The first goal is a metadatabase (Box 2) of Ocean2k-relevant proxy records and model output from publicly-accessible and citable sources, to be completed in January 2012… The second goal is a synthesis paper, based on the metadatabase, addressing the questions in Box 1, and submitted no later than July 2012.

However, the present publication is more than three years behind schedule. According to the SI of the article, the dataset appears to have been mostly collated on schedule (in 2011-12). The calculation of a composite isn’t very hard, so one wonders why there was such a delay.

I’ve taken an interest in high-resolution ocean data for many years and had noticed the OCEAN2K program. I had wondered about its non-publication and had even written to co-author Michael Evans earlier this year (January), wondering what had happened to it:

I notice that the Ocean2K project did not make a synthesis in time for AR5 as had been planned. PAGES2K hasn’t updated the plans for Ocean2K. Are there any updated plans or was it a project that just didn’t work out.

Evans politely wrote back:

the Ocean2k working group did not feel ready to contribute by the AR5 deadline, nor in time to contribute to the PAGES2K Consortium paper published in 2013 (and recently corrected, I understand, with input from you). We’ve recently updated the Ocean2k webpages at the PAGES website (http://www.pages-igbp.org/workinggroups/ocean2k/) to describe progress and future plans. But I see those updates haven’t yet been applied by the system administrator there. I hope they will be shortly

Had the results been more HS-like, it’s hard to believe that the OCEAN2K authors would not have found a way of publishing them in time for AR5. It seems to me that, since the results were “bad”, the authors seem to have felt little urgency.

In making this criticism, I am influenced by my knowledge of the mining business, where promoters are strongly tempted to delay bad drilling results of a program in progress in the hopes that the program gets salvaged by a later hole. For investors and speculators, delayed publication of exploration results are generally a sign of bad results. Influenced by this perspective, I predicted (somewhat acidly) in 2006 that Lonnie Thompson’s delay in publishing Bona-Churchill results indicated that they would not have the Hockey Stick shape of “Dr Thompson’s Thermometer”. They remain unpublished to this day. At the AGU conference last year, Mosley-Thompson’s abstract stated “The δ18O records from the Bona-Churchill and Mount Logan ice cores from southeast Alaska and southwest Yukon Territory, respectively, do not record this strong warming”, confirming my surmise of many years ago.

I plan to do a couple more posts on this study, which, as noted above, has a pretty exemplary SI, thereby facilitating discussion and analysis.



