February 2, 2010


by John P. Costella

March 8, 2006: email 1141398437

Richard Alley writes to Jonathan Overpeck:

Do you know anything about the "divergence problem" in tree rings? Rosanne D’Arrigo talked to the National Research Council yesterday. I didn’t get to talk to her afterward, but it looked to me that they have redrilled a bunch of the high-latitude tree rings that underlie almost all of the high-resolution estimates, and the tree rings are simply missing the post-1970s warming, with reasonably high confidence. She didn’t seem too worried, but she apparently has a paper just out in the Journal of Geophysical Research. It looked to me like she had pretty well killed the "hockey stick" graph in public forum—they go out and look for the most-sensitive trees at the edge of the treeline, flying over lots and lots of trees that are less sensitive but quite nearby, and when things get a little warmer, the most-sensitive trees aren’t sensitive any more; and so the trees miss the extreme warming of the recent times, and can’t reliably be counted as catching the extreme warmth of the Medieval Warm Period if there was extreme warmth then.
Because, as far as I can tell, the "hockey stick" really was a tree-ring record, regardless of how it was labelled as "multiproxy", this looks to me to be a really big deal. And, a big deal that may bite your Chapter of the Intergovernmental Panel on Climate Change Report …

Overpeck responds:

Hi Richard—this issue is one that we refer to in our key uncertaintytable. I believe Keith Briffa was one of the first to write about it, and it is an important issue. I haven’t seen Rosanne’s paper or results myself, but I bet Keith has. I’m cc’ing this to him to see what he thinks.

Keith Briffa responds:

We do need to say something, but as I said in an earlier message, not without more consideration. We should not write something curt on this—ditto the possible direct effects of carbon dioxide. In the push to do all this other stuff, we have had to leave it—to discuss later how to include an "uncertainty issues" bit about recent environmental mess ups. The D’Arrigo paper is not convincing, but we have to do some work to show why, instead of just saying this.

Indeed! Briffa finally realizes that brief public assertions without any scientific backing will no longer be credible.
He continues:

The divergence issue is not universal, and not unrelated to very recent period bias arising from processing methods.

In other words, the problem is real—and its extent unknown. That "processing methods" can completely bias their results completely undermines their stated public confidence that "the science is settled". Indeed, Briffa explains how little they really know—and this is 2006, not 1986:

It is very likely not the threshold problem that D’Arrigo thinks it is. We need money here to work on this, and losing our last application to Europe has messed us up. For now we cannot include anything. I will work on text for the next Intergovernmental Panel on Climate Change Report.

In other words, as of 2006, they needed funding to begin new research to even determine how reliable any of their previous results were. Is this "settled science"?


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