Comments on: Mann's New Divergence "Theory": A Smoothing Artifact

By: Mannomatic Smoothing and Pinned End-points « Climate Audit

Mannomatic Smoothing and Pinned End-points « Climate Audit — Sat, 30 Mar 2013 14:51:13 +0000

[...] to 2007. Recently I discussed Mann’s “explanation” of the Divergence Problem, that it was an artifact of IPCC [...]

By: bender

bender — Thu, 24 Jun 2010 16:05:31 +0000

Grudd’s papers/thesis discuss the divergence problem in detail and indicate that by using the heavily weighted MXD regressions with samples from younger trees in the post 1980 period that the divergence problem is eliminated.

“Eliminated”? As in “rectified”? Or as in “obscured”?

By: bender

bender — Thu, 24 Jun 2010 15:58:03 +0000

If you estimated confidence intervals robustly, then it wouldn’t matter if you reflected or padded the endpoints, because the false information contained at the end of the series would be reflected in an appropriately ever-widening confidence envelope. So the substantive issue here is not how to terminate the series with false data, but how to reflect the appropriate level of uncertainty given lack of knowledge about the future data points beyond the series end.

Trust Mann to dodge the real issue.

By: N Leaton

N Leaton — Wed, 04 Jul 2007 21:06:58 +0000

There is another explanation, and that is that there is a selection bias in the proxies.

If the only proxies are chosen such that the fit the known record, you would expect to see the following.

The proxies are a good fit for the known data – obviously

When the new temperature data comes out, the data diverges.

When you look back at the historical records, the proxies diverge.

Again what is seen. The lack of divergence during the known record, and the extrapolations forward and backward in time showing divergence, is a clear example of this as an explanation.

Nick

By: UC

UC — Tue, 05 Jun 2007 08:05:14 +0000

Here’s a part from Cook et al QRS2004 Fig. 6 :

( http://www.geocities.com/uc_edit/Cook04.jpg )

This kind of divergence, between blue ( proxies 55-70 deg N) and red ( proxies 30-55 deg N) causes bootstrap CIs to expand, am I right? Smaller divergence happens around year 1000, which causes a clear peak in 6.10.c. Loss of growth sensitivity, greater regional variability?

By: jae

jae — Mon, 04 Jun 2007 22:47:45 +0000

95:

My point is that in warm temperate dry climates the tree growth sensitivity is to precipitation not temperature.

I agree that this is usually true. But the claim is that at their altitudinal or latitudinal limits, tree growth is controlled primarily by temperature, not moisture. And this may be true for some locations, but not many, IMHO. Especially in desert-like areas where bristlecone pines live.

By: UC

UC — Mon, 04 Jun 2007 08:48:01 +0000

#84,93 Wasn't that hard to figure out after all, ECS 2002 uncertainty ranges increase in the 1950-1992 period. Bootstrap CIs combined with another divergence problem. See Cook et al QSR2004 Fig. 6

After AD 1950, there is clear divergence, particularly between the North'' and South'' subset chronologies.

By: Philip B

Philip B — Fri, 01 Jun 2007 10:36:57 +0000

More anecdote:

I live in Western Australia and have travelled extensively in the bush. Trees are much larger along watercourses, and away from watercourses tree size clearly declines as you move from higher to lower rainfall areas.

My point is that in warm temperate dry climates the tree growth sensitivity is to precipitation not temperature.

By: UC

UC — Fri, 01 Jun 2007 09:08:48 +0000

#93

No ideas, only a guess (#51):

maybe they didn’t truncate divergent series in 6.10.c

truncated 6.10.b, not truncated 6.10.c, everything is possible

By: Hans Erren

Hans Erren — Fri, 01 Jun 2007 09:01:59 +0000

re 84:
Any idea why the uncertainty band increased recently?