Dendroclimatic transfer functions revisited: Little Ice Age and Medieval Warm Period summer temperatures reconstructed using artificial neural networks and linear algorithms
| Autor: | Jouko Meriläinen, N.G. Makarenko, L. M. Karimova, Mauri Timonen, O. A. Kruglun, Jari Holopainen, Matti Eronen, Samuli Helama |
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| Rok vydání: | 2009 |
| Předmět: |
010506 paleontology
Atmospheric Science 010504 meteorology & atmospheric sciences 01 natural sciences Transfer function Proxy (climate) Paleoclimatology Linear regression Earth and Planetary Sciences (miscellaneous) Dendrochronology lcsh:Science Holocene 0105 earth and related environmental sciences Artificial neural network lcsh:QC801-809 Geology Astronomy and Astrophysics 15. Life on land lcsh:QC1-999 lcsh:Geophysics. Cosmic physics 13. Climate action Space and Planetary Science lcsh:Q Climate model Algorithm lcsh:Physics |
| Zdroj: | Annales Geophysicae, Vol 27, Iss 3, Pp 1097-1111 (2009) Annales Geophysicae, Vol 27, Pp 1097-1111 (2009) |
| ISSN: | 1432-0576 |
| DOI: | 10.5194/angeo-27-1097-2009 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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