Many CA readers have probably been checking out some interesting post at Lucia’s about Stefan Rahmstorf’s opportunistic smoothing of temperature observations in Copenhagen. See here here and here at Lucia’s. Also see David Stockwell’s recent post here and his recent E&E paper on Rahmstorf et al (Science 2007) (Rahmstorf here). Also see the recent Copenhagen Synthesis Report here.
[Update - Jul 2] David Stockwell had an excellent comment on this issue in April 2008 here – see Rahmstorf comment at #14 (thanks to PaulM for drawing this to my attention).
Rahmstorf, a realclimatescientist (a literal translation of the compound German noun), stated in Rahmstorf et al 2007 that the trends were worse than we thought:
The data now available raise concerns that the climate system, in particular sea level, may be responding more quickly than climate models indicate… The global mean surface temperature increase (land and ocean combined) in both the NASA GISS data set and the Hadley Centre/Climatic Research Unit data set is 0.33°C for the 16 years since 1990, which is in the upper part of the range projected by the IPCC.
This was illustrated with the following figure, which has a couple of interesting features. First, the method of smoothing is described only as follows: “All trends are nonlinear trend lines and are computed with an embedding period of 11 years.”
Commenters at Lucia’s and David’s state that Rahmstorf refused to disclose his smoothing method (which proved ultimately to be a sort of Mannian smoothing) on the basis that he did not hold the copyright. Eventually Jean S figured it out and his method was used in David Stockwell’s E&E paper. David has an R-port of the method online (using an R-package ssa presently unavailable for Windows).
Secondly, Rahmstorf has zeroed both models and observations on 1990. I recall some controversy about Willis Eschenbach zeroing GISS models on 1958; I have a vague recollection of Hansen’s dogs saying that this was WRONG. I don’t vouch for this recollection, but, if the events were as I vaguely recall, I don’t see any material difference in Rahmstorf’s centering here.
In David Stockwell’s E&E article, he observed that Rahmstorf’s method applied to updated GISS and CRU resulted in the smooth tapering off. See the online article for the following image. Obviously the tapering off diminishes the rhetorical impact considerably.
Figure 2. Stockwell’s extension of R2007 using the same methodology.
The new Copenhagen Report has an update of the Rahmstorf 2007 diagram (Rahmstorf is said to have added 2007 and 2008 data). The data is said to be smoothed over 11 years (as in Rahmstorf 2007):
Changes in global average surface air temperature (smoothed over 11 years) relative to 1990. The blue line represents data from Hadley Center (UK Meteorological Office); the red line is GISS (NASA Goddard Institute for Space Studies, USA) data… (data from 2007 and 2008
added by Rahmstorf, S.)
However, the Copenhagen diagram doesn’t taper off – a highly important difference in rhetorical effect from the updated version of the Rahmstorf diagram published by David Stockwell.
Figure 3. Rahmstorf’s extension – note the lack of taper occurring in the Stockwell version.
Jean S once again figured this out – Rahmstorf opportunistically changed the smoothing parameter to one that yielded an image that was rhetorically more effective and failed to disclose the change in accounting procedure, falsely reporting that he used the same parameter as in the prior article. This is what the “Community” calls “GARP” – Generally Accepted Realclimate Procedure.
I’ve done a few experiments comparing AR4 A1B models to updated CRU data. More on this tomorrow. I’ve done my own port of Rahmstorfian smoothing to R without using the ssa package – working from first principles. It uses nothing more complicated than svd and a quasi-Mannian padding. (Rahmstorf’s “copyright” pretext is absurd BTW. The Community really has to tell the Team to stop such nonsense.)