Multi-centennial tree-ring record of ENSO-related activity in New Zealand

Journal name:
Nature Climate Change
Volume:
2,
Pages:
172–176
Year published:
DOI:
doi:10.1038/nclimate1374
Received
Accepted
Published online

It is not known how global warming will affect the El Niño/Southern Oscillation (ENSO). The instrumental record is too short to discern centennial-scale trends and modelling results are inconclusive1, 2, 3, 4, 5. Proxy reconstructions indicate that ENSO activity was relatively high during the late twentieth century6, 7, 8, 9, 10, but whether this was unusual in the millennial context remains uncertain. Here we present insights into these issues derived from rings of the kauri tree (Agathis australis), a rare long-lived conifer endemic to the forests of northern New Zealand. Our results indicate that the twentieth century was the most ‘ENSO-active’ century of the past 500 years, but may not be unique in the context of the past 700 years, and that ENSO activity comparable to or elevated above that experienced during the late twentieth century is plausible under warmer-than-present conditions. We also find evidence that there may have been significant changes in the ENSO teleconnection to the New Zealand region during the fourteenth and fifteenth centuries, and of multi-decadal fluctuations in ENSO-related activity building up to the present day. Although these two features may delay the expression of increased ENSO activity in the New Zealand region, our results indicate that New Zealand climate is likely to be more dominated by ENSO-related inter-annual variability as the world continues to warm.

At a glance

Figures

  1. Correspondence between the timing of kauri growth and the characteristic life cycle of ENSO events.
    Figure 1: Correspondence between the timing of kauri growth and the characteristic life cycle of ENSO events.

    a, Median monthly fractional growth of 43 trees at one site over three growing seasons (lines)19. Box-and-whisker plots show inter-tree variance for the 1999–2000 season (10, 25, 50, 75, 90th percentiles). b, Life cycle, in terms of the standardized SOI, of two large El Niños (1982–83, 1997–98) and two large La Niñas (1973–1974, 1988–1989). Dots are correlations (R) of AGAUc10c with concurrent (yellow highlighting) and lagged seasonal mean SOI, plotted against the central month of the season.

  2. Kauri master chronology AGAUc10c composition, statistical quality, spectral character, and evolutive variance and correlation structures.
    Figure 2: Kauri master chronology AGAUc10c composition, statistical quality, spectral character, and evolutive variance and correlation structures.

    a, Mix of source material and estimated expressed population signal29 (EPS). The number of sites, trees and radii at the end of each century is across the top (‘S_T_R:’). The number of radii is accurate, but site and tree numbers are estimates when archaeological timbers contribute (see Supplementary Information for details). b, Annual indices and decadal-scale trend. c, Smoothed, sample-depth-adjusted, running 31-year standard deviation (STD) of AGAUc10c (KauriSTD*, thick line), with estimated 10% and 90% confidence limits (thin lines), superimposed on the results of a Morlet wavelet analysis25 (http://paos.colorado.edu/research/wavelets). Darker greys show increasing spectral power at the corresponding period (right axis) and cross-hatching denotes the ‘cone of influence’, where zero padding has reduced the variance. d, 31-year mean inter-series correlations. Thin red lines are mean inter-radii (RR) and inter-tree (TT) correlations. Thin blue lines are mean correlations of radii (RM) and trees (TM) with the kauri master. The thicker black line (arc-mod) is the correlation between archaeological and modern sub-masters. Smoothed lines in b and c are splines with 50% frequency response at 25 years.

  3. Variance structure of the SOI and selected ENSO proxies, and coincident warming (global and Nino 3 region).
    Figure 3: Variance structure of the SOI and selected ENSO proxies, and coincident warming (global and Niño 3 region).

    a, Smoothed 31-year STD of the SOI (thick grey line, right axis) and five recent multi-proxy ENSO reconstructions (Niño3, ref. 6; R5, ref. 8; UEP, ref. 10; COA, ref. 9; TEL, ref. 9). To facilitate inter-comparison, each multi-proxy STD is plotted as a ratio to the mean STD (that is, averaged over all possible 31-year windows) for the common period 1650–1977. Results for COA and TEL are truncated to the ‘robust’ period defined by ref. 9 and the thick dashed line (3+mean) is the mean through 3–5 multi-proxy analyses. Note that the modern kauri data set is one of the five proxy records used to construct R5 (ref. 8). b, Comparable STD results for ENSO reconstructions based on TEXMEX tree rings9 and NADA-PC1 (ref. 26). Kauri STD* is replotted for comparison, using the same ratio-scaling method. c, Multi-proxy reconstructions of global and Niño-3 region surface temperature16, adjusted to the 1650–1977 base period. Smoothed lines were derived using a 31-year Hanning window30.

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Author information

Affiliations

  1. School of Environment, The University of Auckland, Auckland 1020, New Zealand

    • Anthony M. Fowler,
    • Gretel Boswijk,
    • Maryann Pirie &
    • Jan Wunder
  2. National Institute of Water and Atmospheric Research, Auckland 1010, New Zealand

    • Andrew M. Lorrey
  3. School of Earth Sciences, University of Melbourne, Melbourne, Victoria 3010, Australia

    • Joelle Gergis
  4. Centre de Bio-Archéologie et d’Écologie (UNR 5059), Institute de Botanique, Montpellier 34090, France

    • Shane P. J. McCloskey
  5. Gondwana Tree-Ring Laboratory, Canterbury 7546, New Zealand

    • Jonathan G. Palmer
  6. Forest Ecology, Institute of Terrestrial Ecosystems, Department of Environmental Systems Science, ETH Zurich, CH-8092 Zurich, Switzerland

    • Jan Wunder

Contributions

G.B. led the dendrochronology and was responsible for developing most of the archaeological data set. A.M.L., J.G., S.P.J.M., J.G.P. and J.W. contributed to one or both tree-ring data sets. A.M.L. and J.W. contributed to the kauri seasonal growth study work. M.P. provided pith meta-data for the near-pith truncation resampling experiment. A.M.F. undertook all analyses and wrote the paper (with input from G.B., A.M.L. and J.W.).

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The authors declare no competing financial interests.

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