IPCC AR4 said that the late 20th century was the warmest in 1300 years, relying not just on the Mann Hockey Stick, but on about 10 reconstructions by a relatively small group of authors (the "Hockey Team" or the "Team"). These reconstructions are typically presented in a smoothed version as what I've called here "spaghetti graph" - a term that has spread into wider usage. The IPCC AR4 spaghetti graph is shown below. Wikipedia has a similar spaghetti graph; the NAS Panel had a simplified spaghetti graph. In detail, these reconstructions seem to agree on very little other than that the modern warm period is slightly warmer than the Medieval Warm Period.
The IPCC spaghetti graph contains 10 "multiproxy" reconstructions, 9 of which go back to the MWP.
One important "family" of spaghetti graph reconstructions are highly dependent on strip bark bristlecones/foxtails (a topic which has been much discussed here and elsewhere) but which do not use Yamal. These are "highly dependent" on strip bark bristlecones/foxtails in the sense that their methods do not yield a HS without them. Examples include MBH98-99, Crowley and Lowery 2000, Esper et al 2002 plus the re-statements of the NBH network in Rutherford et al 2005, Mann et al 2007 and Wahl and Ammann 2007.
A second "family" of spaghetti graph reconstructions are dependent on Briffa's Yamal - again, in the sense, that the equivalent calculation using plausible alternatives (e.g. Esper's Polar Urals version instead of Briffa's Yamal) yield different MWP-modern relationships. Examples include Briffa 2000, the closely related D'Arrigo et al 2006 and very recently, Kaufman et al 2009 (despite its first impression of a very different network.)
A third "family" of reconstructions wears both belt and braces - i.e. using both strip bark and Yamal. Key examples are Mann and Jones 2003, Mann et al (EOS 2003), Osborn and Briffa 2006, Hegerl et al 2007. The recent UNEP graphic uses the Mann and Jones 2003 version. A common stratagem in these studies is a leave one out sensitivity - where they show that they can "get" a similar result by leaving out any individual proxy. They can do so safely because they have both Yamal and bristlecones.
In summary, the apparent problems with Briffa's Yamal series impact multiple other studies:
Briffa 2000, Mann and Jones 2003 (used in the recent UNEP graphic), Mann et al (EOS 2003), Jones and Mann 2004, Osborn and Briffa 2006, D'Arrigo et al 2006, Hegerl et al 2007, Kaufman et al 2009 (and of course, Briffa et al 2008).
And because of the non-robust methods used in these studies,
replacing the Briffa Yamal version with a more defensible alternative (such as Esper Polar Urals either individually or in combination with the subfossil Yamal data and Schweingruber russ035w in Yamal)
is going to have a material impact on the medieval-modern differential.
) korvattiin koko käytettävissä olevalla aineistolla, kuuluisa lätkämaila katosi... <puf>
