Hiding the Decline in full view

From 2005

From 2006

Briffa et al 2001 – More on Divergence
After several years of trying, Briffa and Osborn have finally listed the sites used in Briffa et al 2001 and related publications. Briffa had reported results on large networks of over 300 sites collected by Schweingruber. Schweingruber had archived over 400 sites at WDCP.

.... One of the first exercises that I carried out was to calculate a simple average of all the available ring width chronologies in the Briffa et al 2001 network (369 sites – 387 less the 18 unavailable sites.) In this case, I just used the Schweingruber chronologies without trying to re-do using RCS chronologies.

Here’s the result. As you see, there is a noticeable decline in the late 20th century – the “divergence problem.” If this is the average of a large sample of 369 sites, what are the odds that a random selection of say 8 sites has a sharp uptick in the late 20th century. Not very

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