Science published one of the first spaghetti graphs (in Briffa and Osborn 1999 here) as part of an invited comment on the Mann et al 1000-year reconstruction, then hot off the press with its supposed proof that 1998 was the “warmest year” of the millennium. Jones et al 1999, discussed recently here, contained a different spaghetti graph.
Referring to this figure, Briffa and Osborn stated that none of the reconstructions covering the MWP reach modern warmth, and thus the MBH conclusion must “surely be accepted”.
The temperature histories that extend through the medieval period do indicate general warmth (see the figure), although with different maxima (in the 9th, 10th, and 11th centuries). Clearly none of these reach the levels of warmth seen today [although the confidence ranges (not shown here) approach them]. On the basis of their analysis, Mann et al. conclude that the 20th century is anomalously warm. Even with the very limited data available and the problems associated with interpreting many of them as unambiguous measures of hemispheric temperature change, this conclusion must surely be accepted.
The figure from Briffa and Osborn 1999 is shown below with the original caption. It stated that the Briffa version came from Briffa et al 1998 (Nature) and Briffa et al 1998 (Pr Roy Soc London), “processed to retain low-frequency signals”.
Original Caption: Records of past climate… Comparison of NH temperature reconstructions, all recalibrated with linear regression against the 1881-1960 mean April-September instrumental temperatures averaged over land areas north of 20ºN. All series have been smoothed with a 50-year Gaussian-weighted filter and are anomalies from the 1961-90 mean. Instrumental temperatures (1871-1997) are in black, circum-Arctic temperature proxies [1600-1990, from (2 – Overpeck)] are in yellow, northern NH tree-ring densities [1550-1960, from (3 – Briffa et al 1998(Nature); Briffa et al 1998 (Proc Roy Soc London)), processed to retain low-frequency signals] are in pale blue, NH temperature proxies [1000-1992, from (4 – Jones et al 1998)] are in red, global climate proxies [1000-1980, from (5, 6 – MBH99)] are in purple, and an average of three northern Eurasian tree-ring width chronologies [1-1993, from (10 – Briffa et al 2000)] is in green. Although representing a much more restricted spatial coverage than the other series, the last of these (also processed to maintain low-frequency climate information) is included here because of its extended length and because it suggests relatively cooler summer temperatures (at least across northern Eurasia) before A.D. 1000.
The Briffa and Osborn 1999 version of the Briffa MXD reconstruction doesn’t match the version of Briffa et al 1998 or the subsequent version of Briffa et al 2001, both of which were archived. Oddly enough, it does match (after truncation) a version archived at NCDC in December 1998 in connection with Jones et al 1998 (though not used in that article), where it occurs in the second sheet of an Excel file here. To my knowledge, this particular version of the Briffa reconstruction was not otherwise published. (The Briffa reconstruction seems to have been very fluid in this period, as the versions in IPCC TAR Zero Order Draft and First Order Draft appear to be different again and still unaccounted for.)
The following figure overlays a 50-year Gaussian smooth of the digital version at the Jones et al 1998 archive (mean padding after truncation) with approximate rescaling to match the graphic on an excerpt of the figure in Science, proving that the Science figure derives from this version.
Figure 2. Emulation of Briffa and Osborn 1999 Figure 1. The Briffa version is in light blue and is overprinted (thin black) with the Briffa version in the NCDC Jones et al 1998 archive, with 50-year gaussian smooth after truncation to 1960.
As previously reported, this figure, together with Jones et al 1999, are the first two bites of the poison apple of hide the decline. This is what the figure would have looked like, had all the data been shown.
Figure 3. Briffa and Osborn 1999 Figure 1 Excerpt showing the decline (in red).
One can reasonably wonder whether the key conclusion of Briffa and Osborn 1999 – “[despite] the problems associated with interpreting many of them as unambiguous measures of hemispheric temperature change, this conclusion [MBH] must surely be accepted” – would have stood up if the decline had been shown.
As opposed to the other possible conclusion: the “problems associated with interpreting many of them as unambiguous measures of hemispheric temperature change” remain an unsurmounted obstacle and the reason why the Mann reconstruction goes up so sharply when the Briffa reconstruction based on a very large population of temperature sensitive sites goes down remains unexplained and a critical problem within the field.
Briffa and Osborn 1999 contains a very sly reference to the divergence problem:
A number of tree-ring chronologies have displayed anomalous growth or changed responses to climate forcing on different time scales in very recent decades (3 – Briffa et al 1998 (Nature), 9 – Jacoby and D’Arrigo 1995). Understanding the reasons for these changes is important for understanding the causes and limits on past tree growth. Paradoxically, therefore, more work in the recent period is required to better interpret the early proxies. Few of the proxy series run up to the present, however, and updating these will involve considerable effort.
Climategate scientists were well aware of the importance of figures. Briffa and Osborn knew that the graphic with the deletion of the decline would leave a different impression than one that disclosed the decline. The sly wording of the running text compounds the problem. Yes, there are proxies that need updating, but the MXD data used in the Briffa reconstruction came right up to the early 1990s. Unavailability of data is not the reason why the Briffa reconstruction ends in 1960.
Briffa and Osborn 1999 contain a number of sensible caveats about the Mann and other reconstructions, raising caution about the role of bristlecones ( the “amplitude series relating to the first principal component of a group of high-elevation tree-ring chronologies in the western United States”) in the Mann reconstruction and readers are referred to the original here.
These sensible caveats occasioned a flurry of Climategate correspondence among the Team in April and May 1999 ( see 98. 0924120405.txt; 99. 0924532891.txt; 100. 0924613924.txt; 105. 0925829267.txt; 106. 0926010576.txt; 107. 0926012905.txt; 108. 0926026654.txt; 109. 0926031061.txt; 111. 0926681134.txt ) in which Mann objected vociferously to even these reasonable caveats. Even Bradley was nonplussed by Mann’s conduct. In 99. 0924532891.txt on Apr 19, 1999, entitled CENSORED!!!!!, Bradley observed:
As for thinking that it is “Better that nothing appear, than something unnacceptable to us” …..as though we are the gatekeepers of all that is acceptable in the world of paleoclimatology seems amazingly arrogant.
A few weeks later, Bradley commented on Mann’s effort to smooth the waters: “Excuse me while I puke…”
Needless to say, a few years later, when our criticisms appeared, Bradley adopted the attitude that he criticized here: Better that nothing appear, than something unacceptable to us.