Al_U_Card, on 2013-July-01, 05:40, said:
Al is lying again
Quote
Let’s take a closer look at YAD061. In a few years since 1950, this tree had a very high index value of 7 or 8 (meaning these rings are 7 or 8 times wider than would be expected for rings of that age growing in average climate conditions). But this is nowhere near as rare as an 8-sigma value from a Normal distribution, because the TRW index values have strong positive skew (see Fig. PY03 in our SM5) favouring more frequent very high values. It is not the tree with the largest tree index value in the original Briffa (2000) and Briffa et al. (2008) datasets – tree L04551 has larger index values in the 1720s.
There is no clear justification for excluding YAD061, without also excluding other trees with high index values or indeed with low index values – and note the earlier discussion and concerns about post hoc data removal.
However, if you do remove core YAD061 and recreate the old Yamal chronology, the difference is quite limited: see this image. Of course the recent values are lower because you have deliberately searched for and removed the tree with the highest recent index values! But the difference is not enough to affect the main conclusions drawn from that work – clearly not the most influential tree in the world then.
For our new Yamal chronology the inclusion or exclusion of YAD061 makes no perceptible difference to the chronology (see this image; the red line is there, but virtually hidden under the black line). Our conclusions are compatible with those obtained with the old Yamal chronology. So how can YAD06 be the “most influential tree in the world”?!
There are two reasons why YAD061 has no effect on the new chronology and is not an outlier. (1) We have additional data. (2) We have improved tree-ring standardisation processes.
In our new chronology, 17 other trees have peak tree index values that exceed the peak value of YAD061, so it no longer even peaks at the 2nd highest, it peaks at the 18th highest. Of these 18 trees with the highest peak index values, 8 peak values occur in the 20th century and no more than 2 occur in any of the preceding 20 centuries. Clearly the 20th century is a period with enhanced tree-growth, so it is perhaps not surprising to find a tree like YAD061 during this period.
The improved standardisation includes a number of innovations. The key one here is that we now transform the tree index values to follow a normal distribution, which reduces the extremely high index values – e.g. YAD061 peaks around +3.5 standard deviations after this step, compared with the +8 index value before. Together with the expanded dataset, these are the reasons for the lack of sensitivity to inclusion/exclusion of core YAD061. See Fig. 2(a) of this blog to compare “old” and “new” chronologies.
McIntyre overstates the role of this single tree. His post title “YAD06 – the Most Influential Tree in the World” is hyperbole. Maybe he just wants to appear provocative and/or interesting. It has its downsides.
Not least causing others to also overstate things: Booker’s Telegraph piece: “On this astonishing tale, it is no exaggeration to say, could hang in considerable part the future shape of our civilisation.” Really? No exaggeration?
But it can also cause confusion. On 1 March 2010, Lord Nigel Lawson gave evidence to the UK House of Commons Science and Technology Committee that “for a long period before 1421 they relied on one single pine tree” (volume II, evidence EV4, page 9). We don’t know what he meant by this, nor what his source was, and maybe he didn’t really know either – but could he have read a blog post or an article talking about “the most influential tree in the world” and conflated that vague knowledge with questions about tree-ring divergence? It’s possible.
Tim Osborn, Tom Melvin
http://www.realclima...ate/#more-15500