Does car sharing reduce greenhouse gas emissions? Life cycle assessment of the modal shift and lifetime shift rebound effects

Car-sharing platforms provide access to a shared rather than a private fleet of automobiles distributed in the region. Participation in such services induces changes in mobility behaviour as well as vehicle ownership patterns that could have positive environmental impacts. This study contributes to the understanding of the total mobility-related greenhouse gas emissions reduction related to business-to-consumer car-sharing participation. A comprehensive model which takes into account distances travelled annually by the major urban transport modes as well as their life-cycle emissions factors is proposed, and the before-and-after analysis is conducted for an average car-sharing member in three geographical cases (Netherlands, San Francisco, Calgary). In addition to non-operational emissions for all the transport modes involved, this approach considers the rebound effects associated with the modal shift effect (substituting driving distances with alternative modes) and the lifetime shift effect for the shared automobiles, phenomena which have been barely analysed in the previous studies. As a result, in contrast to the previous impact assessments in the field, a significantly more modest reduction of the annual total mobility-related life-cycle greenhouse gas emissions caused by car-sharing participation has been estimated, 3-18% for three geographical case studies investigated (versus up to 67% estimated previously). This suggests the significance of the newly considered effects and provides with the practical implications for improved assessments in the future.Comment: 10 pages, 4 figures (in the end of the file

Consistent Incorporation of Multiple Background Scenarios Into One Background Database: Proposition of a New Approach

When analyzing future impacts of emerging technologies, one has to account for future developments in the background system to ensure temporal consistency between the foreground and background system. This can be achieved by incorporating scenarios into a background database, such as ecoinvent. Combining multiple scenarios can cause conflicts if several scenarios adapt the same process, and can result in an intransparent generation of scenario databases. We propose an approach which enables a transparent and reproducible incorporation of multiple scenarios into a single background database. It builds on and extends already existing brightway libraries, such as wurst and the superstructure. The recently developed brightway library wurst allows to systematically incorporate electricity scenarios from one source, i.e., the integrated assessment model of IMAGE. Incorporating additional scenarios, e.g., with higher regional resolution or for more sectors, such as greener steel production, extends the scope and accuracy of future background databases. An example for regional conflicts would be the incorporation of both average electricity scenarios for Europe and specifically for Germany. Our approach builds on the superstructure principle which produces one scenario database combining the background database with the processes and flows required for the scenarios. Secondly, it generates excel sheets which specify the values of flows for all scenarios. The scenario database and scenario excel sheets can be imported into the activity-browser, the graphical user interface for Brightway. The activity-browser enables a scenario-based LCA calculation and interpretation, which is easy-to-use also for nonpythonic LCA practitioners. Moreover, the generated superstructure database along with the scenario excel sheets can be easily shared. Our approach provides an extension to the superstructure principle to resolve conflicts caused by different scenario sources. We aim at creating a reliable and reproducible workflow to transparently generate a superstructure database which consistently combines scenarios from multiple sources. The goal is to make this approach available to the LCA-community as an open-source tool. Thus, our proposed approach contributes to the usability of background scenarios, and facilitates the cooperation as well as the exchange of scenarios between LCA practitioners

An environmental optimization model for bioenergy plant sizes and locations for the case of wood-derived SNG in Switzerland

Bioenergy from woodfuel has a considerable potential to substitute fossil fuels and alleviate global warming. One issue so far not systematically addressed is the question of the optimal size of bioenergy plants with regards to environmental and economic performance. The aim of this work is to fill this gap by modeling the entire production chain of wood and its conversion to bioenergy in a synthetic natural gas plant both with respect to economic and environmental performance. Several spatially explicit submodels for the availability, harvest, transportation and conversion of wood were built and joined in a multi-objective optimization model to determine optimal plant sizes for any desired weighting of environmental impacts and profits. We find a trade-off between environmental and economic optimal plant sizes. While the economic optima range between 75 – 200 MW, the environmental optima are with 10 – 40 MW significantly smaller. Moreover, the economic optima are highly location specific and tend to be smaller if the biomass resource in the geographic region of the plant is scarcer. The results are robust with regards to the effect on global warming as well as with respect to the aggregated environmental impact assessment methods Ecoindicator ’99 and Ecological Scarcity 2006

Heat, Electricity, or Transportation? The Optimal Use of Residual and Waste Biomass in Europe from an Environmental Perspective

The optimal use of forest energy wood, industrial wood residues, waste wood, agricultural residues, animal manure, biowaste, and sewage sludge in 2010 and 2030 was assessed for Europe. An energy system model was developed comprising 13 principal fossil technologies for the production of heat, electricity, and transport and 173 bioenergy conversion routes. The net environmental benefits of substituting fossil energy with bioenergy were calculated for all approximately 1500 combinations based on life cycle assessment (LCA) results. An optimization model determines the best use of biomass for different environmental indicators within the quantified EU-27 context of biomass availability and fossil energy utilization. Key factors determining the optimal use of biomass are the conversion efficiencies of bioenergy technologies and the kind and quantity of fossil energy technologies that can be substituted. Provided that heat can be used efficiently, optimizations for different environmental indicators almost always indicate that woody biomass is best used for combined heat and power generation, if coal, oil, or fuel oil based technologies can be substituted. The benefits of its conversion to SNG or ethanol are significantly lower. For non-woody biomass electricity generation, transportation, and heating yield almost comparable benefits as long as high conversion efficiencies and optimal substitutions are assured. The shares of fossil heat, electricity, and transportation that could be replaced with bioenergy are also provided

Life cycle assessment of SNG from wood for heating, electricity, and transportation

The conversion of wood to synthetic natural gas (SNG) via gasification and catalytic methanation is a renewable close to commercialization technology that could substitute fossil fuels and alleviate global warming. In order to assure that it is beneficial from the environmental perspective, a cradle to grave life cycle assessment (LCA) of SNG from a first-of-its-kind polygeneration unit for heating, electricity generation, and transportation was conducted. These SNG systems were compared to fossil and conventional wood reference systems and environmental benefits from their substitution evaluated. Finally, we conduct sensitivity analysis for expected technological improvements and factors that could decrease environmental performance