TREE-RING RECORDS FROM NEW-ZEALAND - LONG-TERM CONTEXT FOR RECENT WARMING TREND

Distinct periods of warmth have been identified in instrumental record s for New Zealand and the surrounding southwest Pacific over the past 120 years. Whether this warming is due to natural climate variability or the effects of increasing greenhouse gases is difficult to determin e given the limited length of instrumental record. Longer records deri ved from tree rings can help reduce uncertainties in detection of poss ible causes of climatic change, although relatively few such records h ave been developed for the Southern Hemisphere. In this work, we descr ibe five temperature-sensitive tree-ring width chronologies for New Ze aland which place the recent warming trend into a long-term (pre-anthr opogenic) context. Included are three pink pine (Halocarpus biformis) chronologies, two for Stewart Island and one for the North Island of N ew Zealand. Two silver pine (Lagarostrobus colensoi) series, one each from the North and South Islands, are updated from previous work. The length of record ranges from AD 1700 for Putara, North Island to AD 14 00 for Ahaura, South Island. The pink and silver pine are different sp ecies from those used previously to reconstruct temperatures for New Z ealand. All five chronologies are positively and significantly correla ted with warm-season (November-April) individual station temperature r ecords, a New Zealand-wide surface air temperature index and gridded l and/marine temperatures for New Zealand and vicinity. The highest 20 a nd 40-year growth periods in all five tree-ring series coincide with t he New Zealand temperature increase after 1950. An exception is found for the 40-year interval at Ahaura, the least temperature-sensitive of the five sites. A t-test comparison indicates that these recent growt h intervals are significantly higher (0.01 to 0.0001 level) than any o f those prior to the twentieth century for three of the five sites, da ting as far back as AD 1500. The results suggest that the recent warmi ng has been distinctive, although not clearly unprecedented, relative to temperature conditions inferred from tree-ring records of prior cen turies.