Aggregated indicator to assess land use impacts in life cycle assessment (LCA) based on the economic value of ecosystem services

摘要

Soils are one of earth's essential natural resources, supporting nearly all terrestrial life. By and large, current life cycle impact assessment (LCIA) methodologies are limited in their assessment of potential land use impacts in terms of terrestrial biodiversity loss. The land use life cycle impact assessment (LULCIA) project spearheaded by the United Nations Environment Programme/Society of Environmental Toxicology and Chemistry (UNEP/SETAC) Life Cycle Initiative recently broadened the scope of land use evaluation in life cycle assessment (LCA) by encompassing six additional indicators that represent ecosystem provision and regulation services, as defined in the Millennium Ecosystem Assessment (2005). Although LCIA methodology is more comprehensive with regards to relevant impact pathways linked to land use, the development could potentially decrease the capacity of LCA as a decision support system by increasing the number of indicators from one to seven for the assessment of the land use impact category alone. To overcome this limitation, the project proposes a new LCIA method to estimate the decrease in value of the ecosystem services provided to society due to land use. The six midpoint land use indicators proposed by the LULCIA project are further modeled into a new area of protection, resources and ecosystem services, based on a functional approach. To do so, indicators expressed in biophysical units are converted into monetary units based on the economic valuation of the reduction of a given ecosystem service. The loss of provision services biotic production and fresh water recharge are estimated through productivity loss and water supply cost, respectively. The regulation services erosion resistance and mechanical and physicochemical water filtration are estimated through the cost of erosion mitigation measures and water purification process costs, respectively. The climate regulation potential is estimated through the social carbon cost: a decrease in carbon sequestration by soils is considered equivalent to an amount of carbon emitted in the atmosphere. We also propose to consider the local socioeconomic context by evaluating the economic adaptation capacity of countries: impacts on the resources and ecosystem services area of protection are only accounted for when the country has the capacity to adapt (while indirect impacts would be calculated by assessing the burdens of the adaptation scenario by performing a full LCA of these adaptation measures). The application of the method is illustrated through a case study evaluating the cradle-to-gate land use impacts of three bio-based polymers (biopolyethylene, polylactic acid and thermoplastic starch) produced in Brazil, Italy, Thailand and the United States. Impact scores are not only influenced by the biophysical specificity of the studied systems (e.g. crop yield affecting the inventory flow, type of biome affecting impact characterisation) but also by the local socioeconomic capacity to compensate for an ecosystem service loss and available compensation measures and technologies. In this case study, thermoplastic starch appears to have fewer impacts on land use and ecosystem services than biopolyethylene or polylactic acid. Overall, the research demonstrates the feasibility of further modeling the biophysical indicators of land use into an economic metric.