Comments on ''Reconstruction of the Extratropical NH Mean Temperature over the Last Millennium with a Method That Preserves Low-Frequency Variability''

Moberg, Anders,1961-Stockholms universitet,Institutionen för naturgeografi och kvartärgeologi (INK) (författare)

Christiansen and Ljungqvist have presented an extratropical NH temperature reconstruction using a method (LOC) that they claim ''preserves'' low-frequency variability, at the expense of exaggerated high-frequency variability. Using theoretical arguments and a pseudoproxy experiment, it is demonstrated here that the LOC method is not guaranteed to preserve variability at any frequency. Rather, LOC reconstructions will have more variance than true large-scale temperature averages at all frequencies. This variance inflation, however, can be negligible at those frequencies where the noise variance in individual proxies is small enough to be effectively cancelled when computing an average over the available proxies. Because the proxy noise variance at low frequencies cannot be directly estimated, and thus has to be regarded as unknown, it is safer to regard a reconstruction with the LOC method as providing an estimate of the upper bound of the large-scale low-frequency temperature variability rather than one with a correct estimate of this variance.

NATURVETENSKAP Geovetenskap och miljövetenskap Klimatforskning hsv//swe
NATURAL SCIENCES Earth and Related Environmental Sciences Climate Research hsv//eng
Paleoclimate
Surface temperature
Climate records
Statistical techniques
Climate variability
Physical Geography
naturgeografi

Stockholms universitetInstitutionen för naturgeografi och kvartärgeologi (INK) (creator_code:org_t)

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