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| Titel |
Dendroclimatic transfer functions revisited: Little Ice Age and Medieval Warm Period summer temperatures reconstructed using artificial neural networks and linear algorithms |
| VerfasserIn |
S. Helama, N. G. Makarenko, L. M. Karimova, O. A. Kruglun, M. Timonen, J. Holopainen, J. Meriläinen, M. Eronen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 3 ; Nr. 27, no. 3 (2009-03-04), S.1097-1111 |
| Datensatznummer |
250016442
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| Publikation (Nr.) |
 copernicus.org/angeo-27-1097-2009.pdf |
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| Zusammenfassung |
| Tree-rings tell of past climates. To do so, tree-ring chronologies
comprising numerous climate-sensitive living-tree and subfossil time-series
need to be "transferred" into palaeoclimate estimates using transfer
functions. The purpose of this study is to compare different types of
transfer functions, especially linear and nonlinear algorithms. Accordingly,
multiple linear regression (MLR), linear scaling (LSC) and artificial neural
networks (ANN, nonlinear algorithm) were compared. Transfer functions were
built using a regional tree-ring chronology and instrumental temperature
observations from Lapland (northern Finland and Sweden). In addition,
conventional MLR was compared with a hybrid model whereby climate was
reconstructed separately for short- and long-period timescales prior to
combining the bands of timescales into a single hybrid model. The fidelity
of the different reconstructions was validated against instrumental climate
data. The reconstructions by MLR and ANN showed reliable reconstruction
capabilities over the instrumental period (AD 1802–1998). LCS failed to
reach reasonable verification statistics and did not qualify as a reliable
reconstruction: this was due mainly to exaggeration of the low-frequency
climatic variance. Over this instrumental period, the reconstructed
low-frequency amplitudes of climate variability were rather similar by MLR
and ANN. Notably greater differences between the models were found over the
actual reconstruction period (AD 802–1801). A marked temperature decline, as
reconstructed by MLR, from the Medieval Warm Period (AD 931–1180) to the
Little Ice Age (AD 1601–1850), was evident in all the models. This decline
was approx. 0.5°C as reconstructed by MLR. Different ANN based
palaeotemperatures showed simultaneous cooling of 0.2 to 0.5°C,
depending on algorithm. The hybrid MLR did not seem to provide further
benefit above conventional MLR in our sample. The robustness of the
conventional MLR over the calibration, verification and reconstruction
periods qualified it as a reasonable transfer function for our forest-limit
(i.e., timberline) dataset. ANN appears a potential tool for other
environments and/or proxies having more complex and noisier climatic
relationships. |
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