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Comments on ''Reconstruction of the Extratropical NH Mean Temperature over the Last Millennium with a Method That Preserves Low-Frequency Variability''
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
2012 (English)In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 25, no 22, 7991-7997 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2012. Vol. 25, no 22, 7991-7997 p.
Keyword [en]
Paleoclimate, Surface temperature, Climate records, Statistical techniques, Climate variability
National Category
Climate Research
Research subject
Physical Geography
URN: urn:nbn:se:su:diva-82860DOI: 10.1175/JCLI-D-11-00404.1OAI: diva2:572693
Swedish Research Council, 90751501Swedish Research Council, B0334901
Available from: 2012-12-19 Created: 2012-11-28 Last updated: 2012-12-19Bibliographically approved

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Moberg, Anders
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