Over the past few years, I’ve tried to keep an eye on and review new millennium proxies, posting a number of reviews on high-resolution ocean sediments and new tree ring proxies.
I’ve reported on new tree ring data archived by Jacoby, Rob Wlson, David Meko, Connie Woodhouse and others, leading to some interesting interventions here by Rob Wilson and Mike Pisaric. I’ve kept an eye on ice core data, speleothems and lake sediments as well, periodically canvassing the WDCP site for new additions. So I think I can claim to be as up to date as anyone on new 1000-year proxies, and, by extension, Climate Audit readers are relatively well informed on this topic. There are some relevant new proxies, but not as many as one would think. Also, as Wilson and Pisaric were quick to point out, many new tree ring proxies were not collected as temperature proxies. (More on this matter on another occasion.)
So I was a bit startled when Gavin Schmidt boasted of an increase of 800 or so new proxies in Mann et al 2008 calling for “applause” for the paleoclimatological community:
The number of well-dated proxies used in the latest paper is significantly greater than what was available a decade ago: 1209 back to 1800; 460 back to 1600; 59 back to 1000 AD; 36 back to 500 AD and 19 back to 1 BC (all data and code is available here). This is compared with 400 or so in MBH99, of which only 14 went back to 1000 AD. The increase in data availability is a pretty remarkable testament to the increased attention that the paleo-community has started to pay to the recent past – in part, no doubt, because of the higher profile this kind of reconstruction has achieved. The individual data-gatherers involved should be applauded by all.
Where did these 800 or so proxies come from? How could I have missed the addition of 800 new series to WDP when I was keeping track of additions at least every quarter over the past three years?
Of the total increase (about 794, depending a little on how the MBH population is determined), as shown in the pie chart below, about 83% are tree ring proxies. The next largest increase comes from the Luterbacher series, replacing the long Jones-Bradley instrumental series – not really proxy series at all. The additions to ice core, coral, speleo and sediment series are all relevant and I’ll review them separately. Today I want to look at where the additions to the tree ring population came from.
The next pie chart subdivides the tree ring increase by continent, showing that over half of the total increase came form the North American tree ring network, one that we’ve kept a particularly close eye on for obvious reasons. The other interesting aspect of this graphic is that there was actually a slight (and surprising) decrease in the number of Asia tree ring sites. MBH contained 61 Vaganov series; none of these were retained. There were quite a few Briffa MXD grid sites added in Asia which left matters close to being flat, but still a slight decrease. Curiously no Schweingruber RW series – sites chosen to be temperature sensitive – were included. (These were the sites that originally gave rise to worries about divergence. I suppose the argument would be that these sites are covered by the MXD versions but not all sites are so covered (and, for many sites, multiple indices are used, so there is no rule in Mann et al 2008 limiting a site to one series. I’ll do a separate post on this some time.)
As a bit of a change of pace from the North American network, let’s look at the additions to the Australia-New Zealand network. Here the number of series increased by 48 from 18 to 66. How had I missed this explosion of Australian dendro activity in the past 10 years? Well, I hadn’t. Every single “new” series in Mann et al 2008 ends in 1993 or earlier. Some of the “new” Australian sites (ausl005 ausl010 ausl012 ausl013 ausl019) were collected by Lamarche (of bristlecone fame) back in the 1970s. I then checked at the ITRDB version control to see whether the “new” Mann et al 2008 series had perhaps been archived after 1998, which wouldn’t justify Gavin’s boast but might at least explain the addition. Nope. All the Lamarche series were in the original archive and would have been available to MBH. So series that did not qualify for MBH for some reason or other were permitted in to Mann et al 2008, grossing up the count.
While Mann et al 2008 report tree ring selection criterion (“series must cover at least the interval 1750 to 1970″) , they did not include a material change report discussing any changes in selection criteria from MBH98, the reasons for such changes and their impact. Mann etl al 2000 say of MBH98 selections:
The first year of the chronology was before AD 1626, and it contained at least 8 segments by 1680;
It appears that this criterion has been relaxed somewhat in Mann et al 2008 and this has opened the door for many series that were not included in MBH98 (and which are not directly relevant to medieval-modern comparisons).
We get similar patterns in the other networks. Europe increased from 7 to 90 series, but only 4 series are 1995 or later: a 1995 series from Rob Wilson (germ040), the only Rob Wilson series used in the analysis, a 1996 Kirchhefer series and 3 Kuniholm series from the Aegean (not obvious temperature proxies.)
South America increased from 13 to 78 sites, but all are 1995 or earlier and all but 4 1991 or earlier. Again, the addition of these sites appears to result from changed inclusion criteria.
Now for North America. MBH98 used 281 series ( 11 Jacoby sites and mexi001 directly; 3 Stahle precipitation reconstructions and 219 (232 reported to have been used) in 3 PC networks (North American – 232 (219 used), Stahle SWM – 24, Stahle TXOK – 16). Mann08 uses 694 North American series, an increase of 413 series. The majority of the additional series end before 1985, many in the 1970s, and were in existence long before MBH98 publication. Indeed, only 15% of the new North American tree ring series extend after 1995. Of the new North American series, most appear to be located below altitudinal treeline and are at best precipitation proxies.
There are many puzzling omissions: important data from Alaska and Canada archived by Jacoby and d’Arrigo, by Rob Wilson and Greg Wiles is inexplicably not used, while Mann et al 2008 added series after series that are at best precipitation proxies. In part, the failure to include the Jacoby, Wilson, Wiles etc data is because of a very stale cutoff date: Mann et al 2008 say that they used ITRDB data set as of 2003. which left these series out.
But why have a 2003 cutoff for a study published in Sept 2008 (with calculations as of Dec 2007)? It’s not that hard to keep up to date – I’ve regularly collated ITRDB additions into my tree ring data collation and I don’t have hundreds of thousands of dollars of NSF grants. Mann et al have been lavishly funded by NSF to do exactly the sort of collation that they failed to do. Why didn’t they? It’s not even a matter of heavy equipment or Starbucks availability. This is just computer work. So why not use at least a 2007 ITRDB version? Baffling.
In any event, readers (and Gavin Schmidt) should clearly understand this: only a negligible number of new proxies were collected after MBH98 (about 32, mostly U.S. tree ring). So the increase to 1209 proxies in Mann et al 2008 is not a “remarkable testament” to recent paleoclimate work – it has virtually nothing to do with it, even to the extent of ignoring most primary work that has actually been done in the past decade.
I don’t mind acknowledging primary data collectors. Indeed, I’ve generally been positive in such reviews (as opposed to reviews of the narrow Team) and, despite what my critics may think, this has not gone entirely unnoticed among primary collectors. At the 2007 AGU conference, as I mentioned previously, several eminent oceanographers complimented me on my reviews of ocean sediment literature. My point here is not to disparage primary collectors, but merely to observe that the Mann increase has virtually nothing to do with recent work by primary collectors and has a great deal to do with casting a wider net over old collections, even collections made in the 1970s.
Gavin’s boast is an empty one.