在全球暖化的趨勢下，本研究圖顯了台灣氣溫季節的循環在20世紀早期有顯著的 變化，並且在較暖的未來仍有持續變遷的訊號。使用台灣六個百年測站(台北、台中、 台南、恆春、花蓮、台東)的觀測資料，我們發現自1900-2014年間台灣的夏季有變長 的訊號，各測站定量分析顯示季節大約增長5.29-12.51天/10年，主要歸因於夏季起始 時間的提前與夏季結束時間的延後。相反的，冬季由於起始時間延後與結束時間提前， 因此冬季的長度是有縮短的訊號(2.74-4.63天/10年）。長期的趨勢上測站結果顯示與 全球暖化相同的趨勢，但從台灣測站資料發現1950年代早期，夏季有突然增長的訊號， 其中南部測站特別明顯，但這部分還需要另外研究以找出原因。 利用美國國家環境預測中心與日本氣象廳所產製的重分析資料(20C與JRA55)分析 季節變遷趨勢也呈現與觀測類似的結果。但是相對於觀測資料，重分析資料在夏季變 遷結果較為低估，而在冬季部分又稍微高估。第五階段耦合氣候模式對比計畫(CMIP5) 中15個模式也模擬出類似的趨勢，夏季的季節變遷較為顯著，有超過半數的模式顯示 夏季有劇烈的擴張情況；但多數模式對於冬季的季節變遷估計較弱。雖然模式結果之 間有相當大的差異，但是仍可提供有參考價值的未來季節變遷資訊。以1961-1990年間 的氣候值做季節轉變門檻，在輻射強迫力達到每平方公尺8.5瓦(RCP8.5)的情境下，台 灣氣溫季節變遷的幅度將會比現在還要更大。21世紀末的結果顯示，台灣全年將有超 過50%的日子為夏季，而冬季將減少到最多僅持續一個月左右，甚至有部分模式顯示 2050年後，台灣將沒有冬季存在。

This research reveals, under the influence of global warming tendency, the characteristics of seasonal cycle of temperature in Taiwan have changed significantly since the early 20th century and will continue to change in the warming future. Using six CWB stations (Taipei, Taichung, Tainan, Hengchun, Hualian, and Taitung) daily temperature data, we identify a lengthening (5.29-12.51 days/10years) of the summer duration due to the earlier onset and delayed termination of the season from the1900s to 2014. By contrast, the winter has shortened by 2.74-4.63 days/10years because of delayed onset and early termination. A sudden lengthening of summer season, stations in southern Taiwan in particular, in the early 1950s is also reported. The long-term trend is evidently associated with the global warming trend, whereas the sudden lengthening in the 1950s needs further study to attribute the cause. Similar tendencies are also found in the 20C and JRA55 reanalysis. Both reanalyses exhibit an underestimated (overestimated) 50-year trend in summer (winter) relative to the observed. Most of the CMIP5 models in the historical experiments also simulate a significant expanding trend in the summer duration. However, the winter trend is weaker in the CMIP5 models. Based on the climatological thresholds in current climate, the CMIP5 models project an enhancement of the current trends under the RCP8.5 scenario with high consensus among models. By the end of the 21st century, the summer will last for more than half a year while the winter duration will be shortened to only one month. Some CMIP5 models even project a climate without winter in the late 21st century.