环境足迹的核算与整合框架——基于生命周期评价的视角

环境足迹及其与生命周期评价(LCA)的关系是工业生态学关注的新热点。从探讨环境足迹与LCA的关系入手,以碳足迹、水足迹、土地足迹和材料足迹为例,分别对每一项足迹指标两个版本的核算方法进行了比较。根据清单加和过程的特点,将所有足迹指标划分为基于权重因子和基于特征因子两类,总结了两者的适用性和局限性。在此基础上提出了一个环境足迹核算与整合的统一框架。该框架基于LCA视角建立,但对系统边界和清单数据的要求相对灵活,因而也适用于生命周期不甚明确的情形。研究在一定程度上揭示了足迹指标的方法学实质,同时也为环境影响综合评估提供了一条规范化的途径。

A framework for quantification and integration of environmental footprints: From the perspective of life cycle assessment

Over the past few years, there has been a growing interest in environmental footprints and their relationship to life cycle assessment (LCA), particularly in the field of industrial ecology. Environmental footprints and LCA have much in common, and it is clear that the strengths of LCA in assessing environmental impacts would allow many footprint topics to be addressed under an LCA look-alike framework. This paper starts with the idea of bringing clarity to the nexus between environmental footprints and LCA, an area that remains ambiguous and thus poses an obstacle to the robustness of footprint methods. Methods for accounting for environmental footprints have been reviewed using a selection of existing footprint indicators, including the carbon footprint, the water footprint, the land footprint, and the material footprint. The results demonstrate that each of the four footprints has two versions that apply weighting factors and characterization factors to inventory aggregation, respectively. The distinction between weighting factors and characterization factors is distinct. The former reflect the relative importance they are assigned in a study based on stated or revealed preferences and judgments, whereas the latter are derived from science-based mechanism models that communicate the relative contributions of inventory results to specific impact categories. Consequently, two broad categories of environmental footprints are identified, namely, Version 1.0 (hereafter EF_1.0) and Version 2.0 (hereafter EF_2.0). EF_1.0 and EF_2.0 differ in aspects other than the way they address inventory aggregation. Whereas the two footprint categories have own pros and cons, we argue that only EF_2.0 has the potential to constitute an integrated footprint family due to the risks of double counting and double weighting in the EF_1.0 model. Inspired by the results of two decades of intense debate in the LCA community, this paper establishes a unifying framework consisting of a four-step sub-framework for the accounting of environmental footprints and a three-step sub-framework for the integration of environmental footprints. Although this framework follows the general logic of LCA, it allows for wider applicability than current LCA frameworks as it can be implemented in contexts where there is no clear life cycle or even without an LCA. This paper proposes a composite index for environmental footprints, with the aim of providing decision makers with a holistic picture of the overall environmental impacts of investigated systems at multiple scales, ranging from individual products to the whole world. Our study offers novel insights into the fundamental nature of environmental footprints, particularly for those without LCA expertise. More importantly, it may serve as a starting point for clearing the footprint jungle, and for sparking discussion between research communities that are currently quite disparate, such as those of LCA, the water footprint, and the ecological footprint.