Environmental assessment of biomass based materials : With special focus on the climate effect of temporary carbon storage

Abstract

Goal and scope The goal of this PhD project is to contribute to a more consistent methodology for life cycle assessment (LCA) of biomaterials and to address the environmental performance and perspectives of biomaterials. In particular, it is the goal to develop an approach for dealing with temporary carbon storage in biomaterials, in a way that quantifies the potential climate change benefit in relation to avoiding crossing near-term climatic targets. The geographical scope in this PhD project is global, as the focus is on methodology development and assessment of biomaterials at a global level. The temporal scope is defined by the impact category considered. The technological scope includes both current environmental performance of biomaterials and a discussion of future perspectives, including potentials for future change in their environmental impacts compared to fossil based materials. Background The society today is highly dependent on fossil oil and gas for producing fuels, chemicals and materials, however many of those can alternatively be produced from biomass. The potential of biomaterials to substitute fossil based materials receives increased attention, and their global production is increasing. As the demand for biomaterials increases, so does the need for knowledge about their environmental performance – both in absolute terms and relative to the petrochemical counterparts that they may replace. LCA is a commonly used tool for assessing environmental sustainability of products and systems, accounting for the environmental impacts during their entire lifecycle. However, there are still important gaps in the methodology for LCAs of biomaterials. One such gap is the handling of the potential climate change mitigation value of the temporary storage of carbon that takes place in biomaterials, on which there is currently no consensus. Other important environmental aspects related to biomaterials that are currently not generally included in LCAs are land use and land use change (LULUC) related impacts, such as changes in biogenic carbon stocks (especially including soil organic carbon), surface albedo and biodiversity, as well as potential indirect land use changes (ILUC) of biomaterial production. Potential value of (temporary) carbon storage Due to the existence of climate tipping points, expected to induce dangerous and potentially irreversible changes in the climate system if crossed, temporary carbon storage may have a potential for contributing to mitigating climate change. This potential is in terms of either avoiding the crossing of such expected tipping points (assuming the mitigation scenario RCP3PD, where the atmospheric CO2 concentration peaks within the coming decades) or substantially postpone the crossing (assuming the medium stabilization level scenario RCP6 with a continuous growth in the atmospheric CO2 concentration towards year 2100). Besides the value of the temporary carbon storage in single products, resulting stock changes are expected if petrochemical materials are substituted with biomaterials. These stock changes are more long-term or even permanent, leading to a reduction of carbon fluxes from fossil resources, while potentially increasing fluxes from the atmosphere to the biosphere and via this to the anthroposphere. This leads to a decrease in atmospheric carbon stock and increase in biosphere carbon stock, as well as an increase of biogenic carbon storage in the anthroposphere. This is a trend that will be permanent as long as the biomaterial production is not decreased or phased out again. The CTP approach The general used metric in LCA for assessing climate change, the GWP, does not take into account the need for staying below climatic target levels, and it does not reflect the increased importance of short-lived GHGs in terms of near-term target levels. An approach has been developed in this PhD project for inclusion of the urgency of avoiding crossing dangerous climatic tipping points in the assessment of GHG emissions – the Climatic Tipping Potential (CTP). This approach assesses impacts of GHG emissions up until the potential crossing of a predefined climatic target level. This impact is expressed as a fraction of the atmospheric ‘capacity’ for absorbing the impact without exceeding the target level. The CTP should be seen as complementary to GWP, which should still account for long-term climate change impacts. The CTP method has been further developed to consider the aspect of temporary carbon storage, and illustrate the potential mitigation value of this in relation to avoid crossing dangerous climatic target levels. CTP characterization factors for several GHG development scenarios and a number of other important model parameters are given, making the approach operational for direct inclusion in LCA. Influence of selected non-standard impacts from land use and land use change (LULUC) Some of the impacts associated with LULUC for biomass production, which are often not addressed in LCAs have been addressed through a theoretic case study in this PhD project. These impacts are changes in surface albedo, biogenic carbon fluxes (including SOC) and biodiversity. All three impacts are here found to be potentially important for the environmental performance of the biobased production. Further, potential tradeoffs are found between these impacts. This supports the need for including the best possible assessment of these impacts in LCA, in order to get a realistic picture of the overall impacts from a biomass feedstock crop establishment, and thus downstream products. However, there is a challenge in terms of e.g. the preliminary state of methods, and the requirements to availability of local data. Available biomass potential When discussing the environmental preference of biomaterials relative to fossil-based materials, an important aspect is the sustainable availability of biomass for the production of the biomaterials. It is estimated that there will be enough biomass feedstock available for future biomaterial production without competing with food for the land, even if the entire global need for organic chemicals (including polymers) is based on biomass in the future. However, there is likely to be a competition with bioenergy, including biofuels, for the biomass. Environmental performance of biomaterials Biomaterials generally perform better than equivalent petrochemical materials in terms of fossil fuel savings and reductions in GHG emissions. However in other impact categories they often perform worse, e.g. in terms of eutrophication and acidification, while also entailing land use and related environmental impacts. If using second generation biomass, some of those aspects are likely to improve. It is important to understand that the group of biomaterials is very diverse, both in terms of life cycle pathways and end-products. This gives different environmental profiles within the group, and one should thus be careful with a ‘one profile fits all’ mindset when it comes to environmental assessment of biomaterials. Future perspectives As biomaterials are often based on new, and hence immature, technologies, large improvement potentials are expected for those technologies relative to the competing petrochemical technologies, which are rather mature. Further, potential future shifts in feedstock for both biomaterials and fossil based materials may change their relative environmental performance.