Notice of a new reconstruction by Mann and the Team is in many press clippings today, citing a PNAS article that is not (as I write) online. Rather than clutter other threads, here’s a placeholder thread pending my own response which may take a few days.
Update Sep 2, 2008 2:15 pm: Article online here Article is now online here
The most lengthy notice is here. In the pres release, Mann states that tree ring data is inessential to the present reconstruction, unlike the situation 10 years ago:
“Ten years ago, we could not simply eliminate all the tree-ring data from our network because we did not have enough other proxy climate records to piece together a reliable global record,” said Michael Mann, associate professor of meteorology and geosciences and director of Penn State’s Earth System Science Center. “With the considerably expanded networks of data now available, we can indeed obtain a reliable long-term record without using tree rings.”
It’s interesting that Mann characterizes the past studies in this way as the previous studies had, at the time, made pretty specific claims purporting to be robust to the presence/absence of dendroclimatic indicators.
For example, Mann et al 2000 stated:
We have also verified that possible low-frequency bias due to non-climatic influences on dendroclimatic (tree-ring) indicators is not problematic in our temperature reconstructions.
Or here, Mann states:
Whether we use all data, exclude tree rings, or base a reconstruction only on tree rings, has no significant effect on the form of the reconstruction for the period in question. This is most probably a result of the combination of our unique reconstruction strategy with the careful selection of the natural archives according to clear a priori criteria.
Now CA readers know that the presence/absence of tree rings (actually, bristlecones) had a “significant effect” on the AD1400 network – something that Mann knew as well from the analysis in the amusingly titled CENSORED directory (now deleted from his website), but here Mann artfully illustrated the AD1760 network where the results were advantageous. (In a securities offering, disclosure of the adverse AD1400 results would be obligatory, but seemingly not in climate science where authors are apparently permitted to report only results that go their way.)
the long-term trend in NH is relatively robust to the inclusion of dendroclimatic indicators in the network, suggesting that potential tree growth trend biases are not influential in the multiproxy climate reconstructions.
So this isn’t the first time that Mann has claimed that his results are robust to the presence/absence of tree ring data. He is a serial utterer of this particular claim.
As to what’s in the network: a few predictions (and I’ve not seen the article or the data yet.) Here’s an image from the mongaybay article:
1) the entire MBH98 network (415 series) will be in it. This will include the Graybill bristlecone series.
2) the Briffa MXD network (387 series) used in Rutherford et al (some series of which remain unarchived.) These only go back to 1400 or later and don’t affect the MWP
3) the Luterbacher gridded version in Europe
4) Lonnie Thompson’s tropical ice cores
5) miscellaneous series from Mann and Jones
We’ll find out in due course, but squinting at the map, it doesn’t look like there are a lot of MWP proxies or that the proxy versions are going to differ very much from the usual suspects. So we can expect to see:
6) Briffa’s Tornetrask version, NOT Grudd’s
7) Briffa’s Yamal version and NOT the Polar Urals update
8 ) Graybill’s bristlecone version and NOT Ababneh’s
It doesn’t look like there is anything very much from the ocean sediment world.
Overall, I think that the selections are going to prove pretty familiar and that the MWP proxies are going to be the same tired old ones that we’re used to.