| 1. |
- Charpentier Ljungqvist, Fredrik, et al.
(author)
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Assessing non-linearity in European temperature-sensitive tree-ring data
- 2020
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In: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 59
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Journal article (peer-reviewed)abstract
- © 2019 The Authors We test the application of parametric, non-parametric, and semi-parametric calibration models for reconstructing summer (June–August) temperature from a set of tree-ring width and density data on the same dendro samples from 40 sites across Europe. By comparing the performance of the three calibration models on öpairs” of tree-ring width (TRW) and maximum density (MXD) or maximum blue intensity (MXBI), we test whether a non-linear temperature response is more prevalent in TRW or MXD (MXBI) data, and whether it is associated with the temperature sensitivity and/or autocorrelation structure of the dendro parameters. We note that MXD (MXBI) data have a significantly stronger temperature response than TRW data as well as a lower autocorrelation that is more similar to that of the instrumental temperature data, whereas TRW exhibits a öredder” variability continuum. This study shows that the use of non-parametric calibration models is more suitable for TRW data, while parametric calibration is sufficient for both MXD and MXBI data – that is, we show that TRW is by far the more non-linear proxy.
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| 2. |
- Støve, Bård, et al.
(author)
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A Test for Nonlinearity in Temperature Proxy Records
- 2012
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In: Journal of Climate. - 0894-8755 .- 1520-0442. ; 25:20, s. 7173-7186
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Journal article (peer-reviewed)abstract
- Are temperature proxy records linear recorders of past temperature conditions? A statistical test for linearity is applied to 15 millennial-long proxy records with an annual resolution that was shown to significantly respond to Northern Hemisphere annual mean temperature selected from a collection of 30 proxies. The test, based on generalized additive modeling, shows that most of the proxies can indeed be shown to be linear functions of annual mean temperature, but two proxy records do not appear to have a linear relationship with temperature—this supports the assumption of linearity in most climate reconstruction work. The method tests for nonlinearity in a proxy relative to the group of proxies with which it is being used together. The robustness of the results is tested, and it was found that the results are stable to the choice of proxies. The linearity-testing method is quite general and could in the future be used for larger and more extensive sets of proxies.
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