Though I haven’t posted for a while, I’ve done quite a bit of work on climate recently, though it hasn’t been the sort of work that lends itself readily to blog posts.
I made a presentation at a workshop session in Erice in the third week of August, which, at Chris Essex’ request, was entitled “Year in Review”, focusing on developments in proxy reconstructions. Ross McKitrick made a presentation with an identical title, covering other topics. I spent much of my time on the section on proxy reconstructions in the forthcoming IPCC report, as presaged in the Second Draft, a document which I’ve had for some time, but which I hadn’t yet parsed. In carrying out my own internal review, I re-examined the voluminous literature on individual proxies: ice cores, speleothems, ocean sediments as well as tree rings and “multi-proxy” reconstructions.
The review reminded me of conversations that I had with two prominent though then relatively early/mid-career climate scientists shortly before the announcement of AR4 in January 2007 (mentioned in passing here). The occasion was the AGU conference in December 2006, where there had been a Union session on the NAS panel report on reconstructions, which was then very fresh. Both scientists said that they were convinced by our criticism of the data and methods used by Mann and similar articles and agreed that there would be little progress in the field without the development of new and better data. The more optimistic of the two estimated that this would take 10 years; the more pessimistic estimated 20 years. Although both scientists were tenured, neither was willing to be identified publicly and both required that I keep their identities confidential.
It is now seven years later – 70% of the way through the 10 year process contemplated by the more “optimistic” of the two scientists. This ought to be enough time to see first fruits of any improvement in the proxies themselves. My re-examination of literature on proxies was done with this in mind.
As CA readers are aware, I have been very critical of the repeated use in IPCC studies of proxies with known attributes (e.g. Graybill’s bristlecone chronologies and Briffa’s Yamal). Such “data snooping” – a term used in wider statistical literature – poisons standard statistical tests. In my opinion, real progress in the field will only come when performance and consistency can be demonstrated with out-of-sample proxies of the same “type”.
Conversely, I see little purpose whatever in the application of increasingly complicated and increasingly poorly understood multivariate methods to snooped datasets (e.g. ones with Graybill bristlecones and/or Briffa Yamal). Nor to datasets with gross contamination, such as the Tiljander or Igaliku lake sediments. Nor do I see much chance of progress when specialists are unable to specify the orientation of a proxy ex ante. Or when they use multivariate methods that permit ex post flipping or screening.
Over the past seven years, one sees both tendencies at work.
The production of temperature reconstructions using increasingly complicated multivariate methods on snooped datasets has continued unabated. Mann et al 2008 is the most prominent such article, but there have been others applying very complicated methods to what ought to be a simple problem.
New multiproxy reconstuctions cited by IPCC (e.g. PAGES2K) have also increasingly incorporated lake sediment data, especially since Kaufman et al 2009. Lake sediments have much higher accumulation than ocean sediments and in principle ought to yield higher resolution. However, ocean specialists have focused on a few proxies (O18, Mg-Ca, alkenones) and thereby developed populations that increasingly permit analysis for consistency. In contrast, lake sediment specialists have reported a bewildering variety of proxies (varve thickness, grain size, chironomids, XRay fluorescence, greyscale, pigments, pollen flux, …as well as occasional O18, Mg-Ca and alkenone) without seemingly making any effort at consistency. Lake sediments are also vulnerable to human disturbance e.g. agricultural activity at Korttajarvi (Tiljander) and Igaliku, rendering modern contamination a very real problem. Specialists have rushed to incorporate this still inchoate data into multiproxy reconstructions (Mann et al 2008; Kaufman et al 2009; PAGES2K; Tingley and Huybers 2013), without adequate precautions to ensure that the data is actually a proxy for temperature.
On the other hand, there has also been steady though less publicized progress by specialists on other fronts.
Antarctic ice cores are an “old” proxy, and, in deeper time, O18 data from Antarctic and Greenland ice cores have been perhaps the most important proxy. However, prior to 2013, no annually-resolved Antarctic core with data to the medieval period had been archived. (IPCC AR4 authors refused to show a relatively high (4-year) resolution Law Dome isotope series.) In 2013, three series became available: Law Dome, Steig’s new data from West Antarctic and, miracle of miracles, even an Ellen Mosley-Thompson series from the 1980s – to my knowledge, the first known sighting of Ellen Mosley-Thompson isotope data. (Despite the importance of Antarctica in the Southern Hemisphere, Mann et al 2008 did not use any Antarctic isotope data before the 13th century, instead reconstructing SH temperature with NH data such as bristlecones and contaminated Finnish sediments, as discussed below.) Unfortunately, no Greenland isotope data more recent than 1995 has been archived – the dead hand of Ellen Mosley-Thompson chilling progress in this area.
On a positive note, I am particularly struck by the progress in high-resolution O18 speleothem data, especially in China. This development has passed mostly under the radar, but offers several lines of real progress.
First, some speleothems directly connect the past two millennia to the Holocene. Placement of one- to two-millennium reconstructions in a Holocene context seems to me to be an important somewhat-behind-the-scenes trend in the field. Esper et al 2012, an under-discussed article, has an extremely interesting discussion in respect to tree rings – a topic that I’ve meant to discuss for ages and promise to get to. There has been interesting progress on treelines, including at (of all places) Yamal, again a topic that I’ve meant to discuss and promise to get to.
Second, speleothems provide information on the tropics and subtropics, areas which were abysmally covered by AR4 reconstructions. The interesting population of Chinese speleothems provide important insight into the East Asian monsoon, an insight that is much enhanced by a perspective that extends back through the Holocene to the LGM – a perspective that offers the opportunity to orient the data on a more rational basis that 20th century correlation.
Third, some speleothems are located relatively close to Lonnie Thompson’s tropical ice core data and permit a much clearer perspective on this data – particularly when placed in a Holocene context.
There has also been considerable progress in high-resolution ocean sediment series. Ocean specialists have tended to focus on “deep time”, but in the past decade, “high resolution” data has become more available. Somewhat counterintuitively, the recovery of recent sediments is a serious problem with many ocean cores: uppermost sediments are poorly recovered by piston corers and thus data on the past one-to-two millennia is surprisingly spotty and 20th century data is relatively uncommon.
So there was a both an opportunity and a need for an insightful assessment of work in the field since AR4 by the IPCC AR5 authors. In a recent post, Judy Curry mentioned that a young scientist of her acquaintance had complained of the tension in AR5 between incoming scientists with a fresh perspective and holdovers who were primarily concerned with vindicating/protecting AR4.
The Lead Author roster for the paleoclimate chapter gave grounds for both optimism and pessimism as to whether the section on recent paleoclimate would be insightful.
Giving some grounds for optimism was that Valerie Masson-Delmotte had succeeded Jonathan Overpeck as Coordinating Lead Author. Although committed to IPCC conclusions, Masson-Delmotte is more ecumenical in perspective. Plus, in her own right, she had written competent, interesting and detailed assessments and reconciliations of Antarctic ice cores – precisely the sort of thing that needs to be done with lake sediments and tree rings. For example, Masson et al 2001 canvassed all Holocene Antarctic ice cores, carefully analysing inconsistencies between the information. Some coastal ice cores showed strong recent increases in d18O that were inconsistent with declines in inland sites. Rather than relying on Mannian statistics to sort out inconsistent data, she concluded that the coastal ice cores had been affected by ice flow – with the lower part of the core coming originally from higher elevations. A careful assessment of the proxy literature in accordance with Masson-Delmotte’s own style and standards would have been a welcome change from, for example, Mann’s paean to the Hockey Stick (and Briffa’s obsequious defence).
However, the Lead Author of the section on recent paleoclimatology was Tim Osborn of CRU, a prominent Climategate correspondent. It is impossible to imagine an author more closely allied to Mann, Jones and Briffa and less qualified to provide an independent assessment of their work. In the wake of Climategate, Hans von Storch (among others) had urged CRU authors to step down from IPCC assessment roles, but instead a CRU author was placed in charge of the section that had occasioned the primary past controversy.
In addition, although Briffa, Mann and Jones have attracted most of the attention, Osborn had a personal role in some of the most notorious Climategate incidents and has undeservedly flown beneath the radar. It was Osborn who physically deleted the post-1960 data that hid the decline in the IPCC 2001 report. Osborn was also co-author of the first article that originally deleted the declining data (with the result that the inconsistency between the Briffa and Mann reconstructions was disguised.) It was Osborn who Mann asked not to reveal his “dirty laundry” to the wider community. In a lesser known AR4 hide the decline incident, Osborn suggested that AR4 authors withhold any visual display of the declining Law Dome (Antarctica) isotope series, even though this left the AR4 illustration with only two long Southern Hemisphere proxies (both tree ring series used by Gergis). Osborn was also one of the participants in the delete-all-emails incident. Remarkably, despite his central role in these incidents, Osborn is not listed as having been interviewed by any of the “inquiries” and has sailed pretty much under the radar.
Osborn’s publication record consists almost entirely of joint articles with Briffa – articles which have been rightly reviled on skeptic blogs both for internal inconsistency and assertions that can only be reasonably characterized as cargo cult “science”. I and others have focused on Briffa, but Osborn was also responsible.
Worse, given Osborn’s unrepented complicity in Hide the Decline and similar incidents, no reader can reasonably presume that Osborn has disclosed results adverse to the “message” or that the form of presentation has not been tailored to the advantage of the “message”. As too often, one has to watch the pea.
On balance, the IPCC section on recent paleoclimate mostly lives up to what one would expect from Osborn. Its focus is mainly on multiproxy reconstructions, rather than the data within the reconstructions. Unfortunately, many of these “new” reconstructions use snooped datasets and it takes time to determine what, if anything, is “new” in the reconstruction (or whether it depends on Graybill’s bristlecones or other “old” data). In fairness, AR5 conceded that NH reconstructions prior to AD1200 were heavily dependent on limited data (carefully avoiding the term “bristlecone”) lowering their confidence in reconstructions prior to AD1200, while still displaying them. Remarkably, their NH spaghetti graph ecumenically includes the Loehle and McCulloch 2008 reconstruction. (I haven’t endorsed this reconstruction as being “right” but see no reason why it is unworthy of being in a spaghetti graph.)
Their handling of the Southern Hemisphere is very curious – a topic that I’ll address in detail. However, as a quick preview, readers will recall that Briffa once famously wrote:
I am sick to death of Mann stating his reconstruction represents the tropical area just because it contains a few (poorly temperature representative ) tropical series. He is just as capable of regressing these data again any other “target” series, such as the increasing trend of self-opinionated verbage he has produced over the last few years
Despite presumed awareness of this absurd aspect of Mann reconstructions, IPCC’s Southern Hemisphere disagram relies on Mann et al 2008 reconstructions, which suffer from and exacerbate the defect observed years earlier by Briffa: Mann et al 2008 did not only use bristlecones and contaminated Tiljander sediments for its NH reconstruction, but for its Southern Hemisphere reconstruction. While IPCC did not place great confidence in Mann’s SH reconstruction, it is not clear that it contains any usable scientific information on SH temperature history.
Their section on the tropics is also curious: in the Zero Order Draft, they had observed that there was “nothing unusual” about recent drought or floods in a 1000-year context. At the time, I thought that there was zero chance that this (true) observation would survive the editorial slant. It’s interesting to see how this has evolved. An important new emphasis for recent paleoclimate in AR5 are model-proxy comparisons arising out of the PMIP3 Last Millennium project. I haven’t discussed this interesting enterprise in the past, but it is an important new direction and quite interesting.
In all, there’s lots of fresh material which lends itself to many individual posts. I’ve got much material in inventory and I’ll see what overall conclusions result from the exercise of writing them up.
However, to the extent that I might have hoped that IPCC AR5 would shed fresh insight into the development of recent paleoclimatology, it is mostly very disappointing. Too much rationalization of questionable multiproxy studies and not nearly enough assessment of actual progress on the data front. In a phrase: too much Osborn and not enough Masson-Delmotte.