隨著全球暖化問題日益嚴重，世界各國開始重視溫室氣體減量議題，希望能減緩氣候變遷的速度。循環經濟藉由建立封閉供應鏈來減少原物料開採、加工製造所需之能源，在產品壽命結束後也可以藉由回收系統重新投入產業鏈，大幅減少產品生命週期前後端的能源消耗，因此循環經濟也被認定是一個具有溫室氣體減量潛力的方法。在諸多物質中，塑膠價格便宜且功能廣泛，是帶動經濟發展不可或缺的物質之一，在循環經濟上，塑膠回收再利用不僅可以減少溫室氣體排放，塑膠再生料也可作為塑膠原料投入產業中，因此塑膠也被認為是具有循環減碳的物質。循環經濟涉及產業經濟與廢棄物回收面相，須以較全面的視野來檢視整個產業系統和廢棄物之間的關係。本研究希望以廢棄物投入產出的觀點評估不同塑膠循環情境的減碳潛力，藉由整合產業經濟數據和廢棄物流動數據，建立廢棄物投入產出模型，並結合溫室氣體排放數據評估產業的溫室氣體排放量。因台灣多數原物料仰賴進口，本研究建立之模型亦利用產業關聯程度矩陣，進口品和國產品佔經濟產出的比例，以區分成國內和國外的減碳效益。本研究情境設定分為兩個區塊，以環保署的塑膠包裝循環減量目標和循環經濟情境(加強廢棄物管理、建立封閉供應鏈、延長產品壽命、提升資源使用效率)作為模型分析情境。研究結果顯示，塑膠循環對塑膠製品以外的產業有較大的減碳效果，塑膠製品被回收製成再生料並重新投入塑膠原料相關產業，可以有效減少石油化工與相關化學材料產業的溫室氣體排放量，且塑膠循環再利用比單純減少塑膠使用量更具減碳效益。

As the impacts of global warming have become obvious, countries worldwide have begun to mitigate greenhouse gas (GHG) emissions, hoping to slow down the speed of climate change. Many think tanks have recognized the transition toward circular economies with significant GHGs reduction potential in many countries. The closed supply chains and maximized resource efficiency can reduce the energy requirements in raw material extraction, processing, and manufacturing. In a circular economy, the recycling system can also reuse the materials at the end of the product life cycle. Thus, the carbon footprint of the second life cycle might be significantly reduced. To assess the reduction potential for a circular economic system, a comprehensive analysis should consider the relationship between the industrial and waste management systems. This study evaluated the carbon reduction potential for different plastic circulation policy goals with scenario analyses from the waste input-output perspective. First, we integrated various industrial and waste stream datasets to establish a waste input-output model. Then, we combined GHG emissions data to evaluate the GHG emissions for each sector. The scenarios being analyzed include the plastic packaging reduction goals proposed by the Taiwan EPA and the four circular patterns mentioned in an article of the Journal of Economic Structures. The results show that improvement in plastic recycling has a more carbon reduction on other upstream industrial sectors than the “plastic products” sector. Looking at the inter-industrial linkages, the reduced demand for plastic could effectively reduce the GHG emissions from the petrochemical and chemical material industries.

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