Reconstruction of New Zealand summer temperatures to 1730 ad using dendroclimatic techniques

Abstract

AbstractThe first statistically calibrated and verified reconstructions of past New Zealand temperatures are presented. The reconstructions of summer (December‐March) temperature are derived from a grid of ten subalpine Nothofagus menziesii (Hook. f.) Oerst. and N. solandri (Hook. f.) Oerst. tree‐ring chronologies using dendroclimatological techniques. A regression model where climate in year i is estimated as a function of tree growth in years i−1, i and i + 1 for each chronology is used. Two reconstruction models are developed (for 1853–1915 AD and 1916–1979 AD) and account for 55 per cent and 66 per cent of the temperature variance respectively. Verification of these models accounts for 34 per cent and 42 per cent of the temperature variance over an independent time period. Analysis of the spectral properties of the reconstructions indicates that relatively short‐period variability (<30 years) is better reconstructed than is longer period variability (>60 years). The reconstructions, extending back to 1730 AD, provide statistically reliable estimates of annual to decadal temperature variations. The relative coolness of the 1780s and late 1840s and warmth of the 1750s appear to be notable features of the reconstruction. The reconstructions indicate a far more complicated sequence of palaeotemperature variations than have previously been inferred for New Zealand.