Abstract

Two metrics are typically used to quantify the full greenhouse gas (GHG) balance of biofuel production: the GHG footprint (in kg CO₂-eq/MJ bioenergy produced) and the GHG payback time (in years). The goal of the present study was to quantify and compare spatially explicit GHG footprints and payback times of crop-based bioethanol and biodiesel production, focusing on locations where the four main feedstocks – corn, sugarcane, soybean and rapeseed – are currently cultivated. The largest GHG footprints and longest payback times were found for sugarcane in the tropics, owing to large original carbon stocks in the tropical ecoregions. The lowest GHG footprints and shortest payback times were found in the temperate ecoregions of the USA and Europe, with relatively low initial carbon stocks. For corn, GHG footprints were below the fossil reference and payback times were shorter than 30 years in 71–74% of cumulative production (for sugarcane, in 29–30% of the cumulative production). Soybean and rapeseed have intermediate results, at 49–62% of the cumulative production. The two metrics were highly correlated, except for locations where an infinite payback time was calculated. Overall, GHG footprints and payback times yield similar results when it comes to quantifying GHG balances of biofuels.

摘要

通常使用两个指标来量化生物燃料生产的完整温室气体 (GHG) 平衡：GHG 足迹（以 kg CO _{2 为单位）}-eq/MJ 生物能源生产）和温室气体投资回收期（以年为单位）。本研究的目标是量化和比较基于作物的生物乙醇和生物柴油生产的空间明确的温室气体足迹和投资回收时间，重点是目前种植四种主要原料——玉米、甘蔗、大豆和油菜籽的地点。由于热带生态区的原始碳储量很大，因此热带地区的甘蔗温室气体排放量最大，回收期最长。美国和欧洲的温带生态区具有最低的温室气体足迹和最短的投资回收期，初始碳储量相对较低。对于玉米，温室气体足迹低于化石参考值，并且在 71-74% 的累积产量（对于甘蔗，累积产量的 29-30%）中，回收期少于 30 年。大豆和油菜籽的结果居中，占累计产量的 49-62%。除了计算无限回收时间的位置外，这两个指标高度相关。总体而言，在量化生物燃料的温室气体平衡时，温室气体足迹和投资回收期会产生类似的结果。