以棲蘭山區臺灣扁柏樹輪最大密度重建臺灣北部近千年年均溫

Abstract

樹輪氣候學已廣泛應用於重建具高時間解析度的長期氣候紀錄，有助於釐清區域氣候變異，以及自然與人為氣候驅動因子的相對影響。然而，相較於中高緯度地區，東亞低緯地區之重建年表仍相對稀缺。臺灣位於熱帶與副熱帶交界，地形陡峻，擁有豐富高山環境與適合建構年表之針葉樹種，具備發展長期高解析度氣候重建的潛力。 本研究以臺灣棲蘭山區所採集之臺灣扁柏(Chamaecyparis obtusa var. formosana)樹輪最大密度(Maximum Density)資料為基礎，透過叢集經驗模態分解法(Ensemble Empirical Mode Decomposition)移除非氣候訊號與分離資料所含的內秉模態函數(Intrinsic Mode Functions, IMFs)，並經由各IMF之聚合，嘗試重建以臺北氣象站所代表的臺灣北部地區的年均溫距平序列。研究結果顯示，IMF1–6與IMF789組合可最佳地反映臺北氣象站實測自1897至2020的年均溫距平（以1961至1990年平均為基準）的變異，繼而重建自公元1064年至2020年，長達957年臺灣北部地區年均溫距平序列。 重建結果指出，臺灣北部在11世紀中葉至12世紀中葉與小冰期期間（約公元1650年至1900年）出現顯著冷期，與北半球高緯地區之氣候變異趨勢一致。此外，公元1256年至1414年間則呈現極端高溫現象，多數年份年均溫距平值超過重建模式兩倍RMSE的門檻，顯示極端高溫事件亦可能源於自然氣候變異。 進一步探討重建溫度與外在自然因子的關聯性，顯示Maunder與Dalton等太陽極小期與重建冷期具有一致性，火山爆發事件如1257年Samalas及1600年Huaynaputina火山爆發後亦對應短期降溫現象。遙相關(Teleconnections)分析亦指出，重建序列與歐亞大陸大部分地區、西太平洋暖池與黑潮延伸區等區域呈正相關，顯示可反映東亞季風系統與熱帶海洋熱輸變化。相較之下，與聖嬰南方振盪代表指標Niño4之相關性空間結構較零散，推測其氣候影響可能具非線性與時間滯後特性；而與大西洋多年代際振盪則呈現顯著之「領先」關係，顯示臺灣北部地區氣候變異可能與大西洋跨洋遙相關機制有所關聯。 綜上所述，本研究不僅建立目前臺灣最長的高解析溫度重建序列，亦初步釐清低緯度地區氣候與太陽活動、火山事件及海氣交互作用之關聯，對理解東亞低緯度地區的長期氣候變異具有一定應用價值。

Dendroclimatology has been widely applied to reconstruct long-term climate variability with high temporal resolution, contributing to the understanding of regional climate change and the relative roles of natural versus anthropogenic forcing. However, high-resolution tree-ring-based climate reconstructions remain scarce in the low-latitude regions of East Asia. Taiwan, situated at the boundary of the tropics and subtropics and characterized by steep topography and abundant coniferous forests in high mountain areas, holds great potential for long-term climate reconstruction. This study presents a high-resolution temperature reconstruction for northern Taiwan spanning 957 years (1064–2020 CE) based on maximum latewood density data from tree-rings of Chamaecyparis obtusa var. formosana collected in the Chilan Mountain Area. This study applied the ensemble empirical mode decomposition (EEMD) technique to remove non-climatic trends and isolate different intrinsic mode functions (IMFs). The combination of IMF1–6 and IMF789 best reflected the variability of the mean annual temperature anomaly (relative to the average of 1961 to 1990 annual means) at Taipei Station between 1897 and 2020. This study thus used the combination to reconstruct the annual temperature anomaly between 1064 and 2020 CE for northern Taiwan. The reconstructed series captured major climate episodes. The reconstruction results indicated two pronounced cooling periods, one in the mid-11th to the mid-12th centuries and the other one in the Little Ice Age (ca. 1650–1900 CE), which aligned closely with other reconstructed temperature anomalies in high-latitude regions of the Northern Hemisphere. Additionally, a distinct warm phase was also detected between 1256 and 1414 CE, during which the mean annual temperature anomalies for most years exceeded the two times reconstruction model's RMSE threshold, underscoring the role of natural climate variability. Examinations of external forcing factors revealed a clear correspondence between the reconstructed series and solar activity minima (e.g., Maunder and Dalton), suggesting that solar activity may influence the climate of low latitudes. Short-term cooling periods were also observed following certain significant volcanic eruptions (e.g., the 1257 Samalas eruption and the 1600 Huaynaputina eruption), although the responses appeared regionally heterogeneous and inconsistent. Teleconnections revealed that the reconstructed temperature series were positively associated with most of the Eurasia regions, the western Pacific warm pool, and the Kuroshio Extension, indicating that the reconstruction reflected the coupled dynamics of ocean-atmosphere systems. In contrast, correlations with Niño4 region sea surface temperature were spatially weak and fragmented, suggesting a nonlinear and time-lagged El Niño-Southern Oscillation influence on northern Taiwan. A significant leading relationship was observed with the Atlantic Multidecadal Oscillation, indicating a possible trans-basin teleconnection. In summary, this study presents the longest high-resolution temperature reconstruction for Taiwan to date, offering new insights into the relationships between low-latitude climate variability, solar forcing, volcanic activity, and ocean-atmosphere interactions. The findings enhance the understanding of long-term climate variability in East Asia.