I think that Mann et al. are on the horns of an interesting dilemma on variance scaling (and there is no injustice in this.) MàÆàⵢerg et al. , following von Storch et al. , argue that the use of regression-based methods in MBH98/99 result in the lesser variability in the shaft of the hockey-stick. Here are some excerpts:
Different calibration methods (regression in the work of Mann and Jones versus variance scaling in this study) are another reason [for differing variabilities]….Recent findings[von Storch et al., 2004], however, suggest that considerable underestimation of centennial Northern Hemisphere temperature variability may result when regression-based methods, like those used by Mann et al., are applied to noisy proxy data with insufficient spatial representativity…To calibrate the reconstruction, its mean value and variance were adjusted to agree with the instrumental record of Northern Hemisphere annual mean temperatures in the overlapping period AD 1856–1979 (Fig. 2b). This technique avoids the problem with underestimation of low-frequency variability associated with regression-based calibration methods[von Storch et al, 2004]…
The irony of this is that I’m pretty sure that MBH98 contains an unreported variance scaling step. In our emulation of MBH98, we need to carry out a variance scaling after the regression steps in order to get close to their temperature reconstruction so I’m 99% sure that MBH98 has variance scaling as well. (The reason for the hockey stick being the hockey stick is the bristlecone pine imprint as we’ve discussed elsewhere. )
Here’s their dilemma: do they rebut the criticism of von Storch and MàÆàⵢerg by stating that the criticisms are invalid because there is still another undisclosed step in MBH98? But if they do that, then they would have to issue Corrigendum #3 as it were (presuming that a Corrigendum #2 is de facto in place with the incorrectly disclosed PC methods). If they now argued that they included a variance scaling step, would they have to produce their source code (and who knows what lurks there)?