北魏孝文帝將首都從平城遷到洛陽，史家認為是拓跋宏考量當時政治、經濟、軍事、文化等多元因素所做的決定，也有認為是他的漢化思維所誘發的舉動。然而司馬光在資治通鑑所載「魏主以平城地寒，六月雨雪，風沙常起，將遷都洛陽」，強調當時之惡劣氣候是南遷的主因。 本文採三個步驟來比較平城古今氣候：(1)利用近年之地面氣象觀測紀錄，了解大同之氣候現況。(2)演譯古詩詞及古文獻中之環境信息，重塑平城之古氣候。(3)根據樹輪、冰芯、及湖泊沉積物等具有時間序列的地球科學資料，展現出西元五百年左右的氣候環境。 研究結果顯示，不論是演譯史籍文獻或是根據地球科學資料，平城在北魏時代的氣溫低於現今。從文史記載分析北魏時代霜期的長短，推估408AD-537AD間的平均最低溫度，至少比今日低0.820℃，而在479AD-509AD的最冷時期，其平均最低溫度則比今日低2.66℃。寒冷氣候應是拓跋宏南遷的重要原因之一。 歷史文獻對古環境之描述存在著定性之氣候信息，而技術逐漸成熟的地球科學分析又能提供時間序列的數化依據，若能妥善利用此兩項工具，對重建二千年來氣候變化的時間序列資料是具有重大意義的。

About 1500 years ago, Emperor Tuo-ba-hong of the Bei-wei Dynasty moved his capital from Ping-cheng, in Shan-xi province to Luo-yang. Questions were raised as to why he decided to relocate his capital. Was it because of political, economic, military and cultural factors? Or was it because of his Han-cultured personality that drove him to do so? Or was it because of the cold climate? Three sets of analyses were performed to seek answers to these questions. The first analysis examines the climatic situation by using temporal surface meteorological records. The second analysis infers the ancient climatic environment based on poems and historical documents. The third analysis looks at evidence provided by tree-ring, ice core and lake sediment data available over the time span going as far back as the Bei-wei dynasty. The results from these three approaches revealed that the climate of Ping-cheng in the past was colder than the present situation. The mean minimum temperatures are estimated to be lower by 0.82℃ during 408AD-537AD and by 2.66℃ during 479AD-509AD respectively when compared with the present In evaluating climate change, it is suggested that both qualitative and quantitative methods should be used as analytical tools for the reconstruction of historical climate in the past 2000 years.