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| Titel |
The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability |
| VerfasserIn |
B. Christiansen, F. C. Ljungqvist |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 8, no. 2 ; Nr. 8, no. 2 (2012-04-18), S.765-786 |
| Datensatznummer |
250005483
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| Publikation (Nr.) |
 copernicus.org/cp-8-765-2012.pdf |
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| Zusammenfassung |
| We present two new multi-proxy reconstructions of the extra-tropical
Northern Hemisphere (30–90° N) mean temperature: a
two-millennia long reconstruction reaching back to 1 AD and a 500-yr
long reconstruction reaching back to 1500 AD. The reconstructions are
based on compilations of 32 and 91 proxies, respectively, of which
only little more than half pass a screening procedure and are included
in the actual reconstructions. The proxies are of different types and
of different resolutions (annual, annual-to-decadal, and decadal) but all
have previously been shown to relate to local or regional temperature. We
use a reconstruction method, LOCal (LOC), that recently has been shown
to confidently reproduce low-frequency variability. Confidence intervals
are obtained by an ensemble pseudo-proxy method that both estimates
the variance and the bias of the reconstructions. The two-millennia
long reconstruction shows a well defined Medieval Warm Period, with a
peak warming ca. 950–1050 AD reaching 0.6 °C relative to the
reference period 1880–1960 AD. The 500-yr long reconstruction confirms
previous results obtained with the LOC method applied to a smaller
proxy compilation; in particular it shows the Little Ice Age cumulating
in 1580–1720 AD with a temperature minimum of −1.0 °C
below the reference period. The reconstructed local temperatures,
the magnitude of which are subject to wide confidence intervals,
show a rather geographically homogeneous Little Ice Age, while more
geographical inhomogeneities are found for the Medieval Warm Period.
Reconstructions based on different subsets of proxies show only small
differences, suggesting that LOC reconstructs 50-yr smoothed extra-tropical
NH mean temperatures well and that low-frequency noise in the proxies
is a relatively small problem. |
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