Severinghaus and “Hide the Decline”
By Steve McIntyre
One of the very first contributions to realclimate was an FAQ from Jeff Severighaus on Dec 3, 2004. A year earlier, Severinghaus attempted (unsuccessfully) to get an explanation of the “divergence” problem from Mann and the rest of the Team. Severinghaus had become interested in the question following a presentation by Tom Karl of NOAA in which he had used a figure from Briffa and Osborn 2002, in which he wondered about the “flat” response of the tree ring proxies in the last half of the 20th century.
In nearly all defences of the deletion of the decline in spaghetti graphs that yield a rhetorical effect of coherence between the Briffa and other reconstructions in the last half of the 20th century, it’s been argued that the divergence problem was fully disclosed in a couple of 1998 Briffa articles and that this disclosure in the original technical literature constituted sufficient disclosure – a point that I contested long before Climategate.
The Severinghaus exchange is highly pertinent to this issue. Severinghaus was a climate scientist who was not a specialist in the area who asked specifically about a diagram in which the decline had been hidden (though Severinghaus was unaware that the decline had been hidden.)
Severinghaus was concerned merely by the flattening of proxy response. One can only imagine how the exchange would have read had Severinghaus been aware that the Briffa reconstruction actually declined sharply. Read and see whether Mann, Jones and/or Briffa drew Severinghaus’ attention to the early articles in which the divergence problem was disclose.
On the afternoon of Feb 1, 2003 California time (emails -2545, 19, 4355 Feb 2, 2003 00:15 GMT), Severinghaus wrote to Tom Karl of NOAA about his presentation at the MIT Global Change Forum the previous day. Severinghaus asked about the “flat” response of tree rings to late 20th century warmth, referring to an article by Briffa and Osborn in Science (2002). The diagram in question would be the following:
Figure 1. Briffa and Osborn (Science 2002) Figure 1.
Severinghaus observed that this lack of response is an “embarrassment” and that it “casts doubt on the integrity of the proxy”:
Subject: tree rings and late 20th century warming
Date: Sun, 2 Feb 2003 16:15:04 -0800
From: Jeff Severinghaus
Dear Dr. Karl,
I enjoyed your presentation yesterday at the MIT Global Change forum. You may recall that I asked about the failure of tree rings to record the 20th century warming. Now that I look at my records, I realize that I remembered this wrongly: it is the LATE 20th century warming that the tree rings fail to record, and indeed, they do record the early 20th century warming.
If you look at the figure in the attached article in Science by Briffa and Osborn, you will note that tree-ring temperature reconstructions are flat from 1950 onward. I asked Mike Mann about this discrepancy at a meeting recently, and he said he didn’t have an explanation. It sounded like it is an embarrassment to the tree ring community that their indicator does not seem to be responding to the pronounced warming of the past 50 years. Ed Cook of the Lamont Tree-Ring Lab tells me that there is some speculation that stratospheric ozone depletion may have affected the trees, in which case the pre-1950 record is OK. But alternatively, he says it is possible that the trees have exceeded the linear part of their temperature-sensitive range, and they no longer are stimulated by temperature. In this case there is trouble for the paleo record. Kieth Briffa first documented this late 20th century loss of response.
Personally, I think that the tree ring records should be able to reproduce the instrumental record, as a first test of the validity of this proxy. To me it casts doubt on the integrity of this proxy that it fails this test.
Severinghaus obviously didn’t know that the Briffa and Osborn diagram had deleted the post-1960 decline from the Briffa reconstruction. Had they shown the actual data, the diagram would have looked more like the one shown below.
Read the full post at Climate Audit