Conceptualising attributional LCA is necessary for resolving methodological issues such as the appropriate form of land use baseline

Purpose

The purposes of this commentary are to further an on-going debate concerning the appropriate form of land use baseline for attributional life cycle assessment (LCA) and to respond to a number of arguments advanced by Soimakallio (Int J Life Cycle Assess 20:1364–1375, 2016). The commentary also seeks to clarify the conceptual nature of attributional LCA.

Methods

The overarching approach for resolving the question of the appropriate form of land use baseline for attributional LCA is to clarify what attributional LCA is seeking to represent, i.e. methodological questions can only be resolved if it is clear what the method is seeking to do. An illustrative example is used to explore the different results produced by ‘natural regeneration’ and ‘natural’ baselines.

Results and discussion

It is proposed that attributional LCA should be conceptualised as an inventory of anthropogenic impacts, conceptually akin to other forms of environmental inventory, such as national GHG inventories. The use of natural regeneration baselines is not consistent with this conceptualisation of attributional LCA, and such baselines necessitate further ad hoc or arbitrary adjustments, such as arbitrary temporal windows or the inconsistent treatment of natural emissions.

Conclusions

The use of natural regeneration baselines may be motivated by the impulse to make attributional LCA both an inventory-type method and an assessment of system-wide change. Pulling attributional LCA in two different directions at once results in a conceptually and methodologically incoherent method. The solution is to recognise attributional LCA as an inventory-type method, which therefore has distinct but complementary uses to consequential LCA, which is an assessment of system-wide change.

     

Critical review of guidelines against a systematic framework with regard to consistency on allocation procedures for recycling in LCA

Purpose

Multifunctionality in LCA can be solved by several allocation procedures. Various official guidelines give divergent recommendations in which allocation procedure to apply, and up to now, no consensus has been reached. We aim to identify the obstacles to a consistent allocation approach that can be applied to all product categories and is supported by a broad range of stakeholders.

Methods

Based on a systematic framework for consistent allocation, developed by Schrijvers et al. (Int J Life Cycle Assess, 2016), we identify five review criteria that indicate the degree of consistency in the proposed allocation procedure of official guidelines. Several relevant guidelines, i.e. ISO 14044, ISO/TR 14049, ISO/TS 14067, the ILCD Handbook, BP X30-323-0, PAS 2050, the Greenhouse Gas Protocol, EN15804, PEF Guide and guidance documents for EPDs and PCRs, are reviewed according to these criteria.

Results and discussion

None of the investigated guidelines fully follows the systematic framework for allocation. Often, different approaches are recommended for co-products and recycled materials, although the boundary between these flows is not always clear. Many guidelines do not recognize the existence of different LCA goals; therefore, elements of attributional and consequential LCAs are often mixed. The market situation of the recycled material is not always taken into account, e.g. in the mandatory 50/50 method of the PEF Guide. The ILCD Handbook and the General Programme Instructions for the International EPD® System provide most consistent guidance. We argue that consistency does not require a one-formula-fits-all method, as this would favour some product categories and only responds to a certain LCA goal.

Conclusions and perspectives

A critical review of guidelines against a systematic framework for allocation of co-products and recycled materials shows that few guidelines propose a consistent allocation approach. The main obstacles for consistency are the different approaches for co-production and (different types of open-loop) recycling and disregarding of different LCA goals and recycled material markets. We recommend to include material specific guidance in Product Category Rules on the determination of market prices, quality determining factors and relevant material properties for different applications.

     

Customizing CO<Subscript>2</Subscript> allocation using a new non-iterative method to reflect operational constraints in complex EU refineries

Purpose

Developing a robust method for CO₂ allocation in oil refineries is an ongoing debate within the life cycle assessment (LCA) community. Several methodologies reported in the literature, mostly performing sequential and iterative calculations, tend to be biased toward diesel at the expense of gasoline, failing to properly consider the role played by hydrogen. This paper develops a new non-iterative refinery CO₂ allocation method to explore the concept of customized allocation to overcome the inherent bias in standard methods.

Methods

The allocation methodology is based on a system of linear equations built around the material and energy balances of a refinery. After describing the process of building such system, it is shown that the carbon allocation values of all final products and intermediate streams are directly obtained by solving it. A numerical example of CO₂ emission allocation to major refinery products is provided from an optimized refinery linear programming (LP) case for the European refining industry, based on literature projections for 2020.

Results and discussion

The paper presents the key emission sources in the European refinery sector, and by using a standard mass-based allocation technique, we show that the carbon intensities of refined petroleum products derived using the non-iterative method are consistent with other studies. We confirm the findings that the standard allocation typically used in attributional refinery LCA tends to reward diesel to the detriment of gasoline. We attempted reconciling this by applying a reallocation factor to customize the CO₂ allocation to represent the “real” economic purposes of process units reflecting the constraints European refineries face today. This moderated the octane production effects given the important role the reformer plays in hydrogen co-production, where the emission burden of highly knock-resistant reformate is redistributed to hydrogen and carried through to diesel.

Conclusions

By customizing the allocation of CO₂, we demonstrated that the differences between a consequential and an attributional approach in refinery LCA can partly be reconciled. We now run into the risk of increasing the subjectivity of the attributional method by using “judgment calls” to decide on the choice of weightage to be applied. We invite the wider LCA practitioners to further investigate the use of this new non-iterative method for allocating CO₂ and explore the concept of reallocation factors as means to customize emission allocation.

     

Attributional and consequential LCA in the ILCD handbook

Purpose

This discussion article aims to highlight two problematic aspects in the International Reference Life Cycle Data System (ILCD) Handbook: its guidance to the choice between attributional and consequential modeling and to the choice between average and marginal data as input to the life cycle inventory (LCI) analysis.

Methods

We analyze the ILCD guidance by comparing different statements in the handbook with each other and with previous research in this area.

Results and discussion

We find that the ILCD handbook is internally inconsistent when it comes to recommendations on how to choose between attributional and consequential modeling. We also find that the handbook is inconsistent with much of previous research in this matter, and also in the recommendations on how to choose between average and marginal data in the LCI.

Conclusions

Because of the inconsistencies in the ILCD handbook, we recommend that the handbook be revised.

     

Estimation of the size of error introduced into consequential models by using attributional background datasets

Purpose

A systematic comparison is made of attributional and consequential results for the same products using the same unit process database, thus isolating the effect of the two system models. An analysis of this nature has only recently been made possible due to the ecoinvent database version 3 providing an access to both unallocated and unlinked unit process datasets as well as both attributional and consequential models based on these datasets. The analysis is therefore limited to the system models provided by ecoinvent.

Methods

For both system models, the analysis was made on the life cycle inventory analysis (LCIA) results as published by ecoinvent (692 impact categories from different methods, for 11,650 product/activity combinations). The comparison was made on the absolute difference relative to the smallest absolute value.

Results and discussion

The comparison provides quantified results showing that the consequential modelling provides large differences in results when the unconstrained (marginal) suppliers have much more/less impact than the average, when analysing the by-products, and when analysing determining products from activities with important amounts of other coproducts.

Conclusions

The analysis confirms that for consequential studies, attributional background datasets are not appropriate as a substitute for consequential background. The overall error will of course depend on the extent to which attributional modelling is used as part of the overall system model. While the identified causes of differences between the attributional and consequential models are of general nature, the identified sizes of the errors are specific to the way the two models are implemented in ecoinvent.

     

Are we still keeping it “real”? Proposing a revised paradigm for recycling credits in attributional life cycle assessment

Purpose

End-of-life (EoL) recycling poses a challenge to many practitioners today due to the availability of different calculation approaches and the lack of scientific consensus, which is fueled by academic research and vested industry interests alike. One of the main challenges in EoL modeling is the credible calculation of the appropriate recycling credit in open-loop and closed-loop situations.

Methods

We believe that part of the challenge is caused by a lack of understanding of the underlying recycling paradigm, which refers to the meaning that is assigned to the recycling credit. Referred to as “system expansion through substitution” and “future displacement of primary production,” the two predominant paradigms are delineated from each other followed by a discussion of their remaining challenges.

Results and discussion

Based on these considerations, we propose a revised paradigm based on embodied burdens that is able to alleviate many of the most pressing issues associated with material recycling in attributional life cycle assessment.

Conclusions

With this discussion paper, we look forward to a productive and lively debate on the matter.

     

Choice of land reference situation in life cycle impact assessment

Purpose

Land use life cycle impact assessment is calculated as a distance to target value—the target being a desirable situation defined as a reference situation in Milà i Canals et al.’s (Int J Life Cycle Assess 12(1):2–4, 2007) widely accepted framework. There are several reference situations. This work aims to demonstrate the effect of the choice of reference situation on land impact indicators.

Methods

Various reference situations are reported from the perspective of the object of assessment in land in life cycle assessment (LCA) studies and the modeling choices used in life cycle land impact indicators. They are analyzed and classified according to additional LCA modeling requirements: the type of LCA approach (attributional or consequential), cultural perspectives (egalitarian, hierarchist or individualist), and temporal preference. Sets of characterization factors (CF) by impact pathway, land cover, and region are calculated for different reference situations. These sets of CFs by reference situation are all compared with a baseline set. A case study on different crop types is used to calculate impact scores from different sets of CFs and compare them.

Results and discussion

Comparing the rankings of the CFs from two different sets present inversions from 5% to 35% worldwide. Impact scores of the case study present inversions of 10% worldwide. These inversions demonstrate that the choice of a reference situation may reverse the LCA conclusions for the land use impact category. Moreover, these reference situations must be consistent with the different modeling requirements of an LCA study (approach, cultural perspective, and time preference), as defined in the goal and scope.

Conclusions

A decision tree is proposed to guide the selection of a consistent and suitable choice of reference situation when setting other LCA modeling requirements.

     

Consequential and attributional environmental assessment of biofuels: implications of modelling choices on climate change mitigation strategies

Purpose

The study aims to assess climate change mitigation potentials when using biomass-based fuels to replace fossil energy under consequential and attributional modelling approaches. The objectives are also to determine policy implications and to recommend the specific contexts suitable for each modelling choice by using specific illustrative cases on biofuels.

Methods

Consequential and attributional modelling approaches are chosen for life cycle greenhouse gas emission assessment of several bioenergy options. The assessed functional unit is 1 MJ of energy from molasses-based ethanol, palm-based biodiesel and electricity production from rice straw. The fossil fuel comparators are gasoline (for molasses-based ethanol), diesel (for palm-based biodiesel) and coal and gas (for rice straw). The substituted and substituting product systems are modelled under the global and national markets depending on the market delimitation of each product.

Results and discussion

The climate change mitigation potentials when using different approaches are dissimilar, because the affected product systems being included in the analysis are not the same. The palm biodiesel could reduce greenhouse gas emissions. The molasses-based ethanol and rice straw-based electricity may or may not mitigate the climate change, since it depends on the methodological choices as well as the baseline situations of the product systems being investigated. The main characteristics of consequential modelling as additionality and the inclusion of only actually affected processes under market-based mechanisms while those of attributional modelling as specification and attribution/allocation have limitations. The limitations lead to potential risks on unintended and undesirable consequences (for the attributional model), unfairness and sub-optimisation (for the consequential model) in policy recommendations.

Conclusions

This research clearly illustrates how certain modelling choices affect the climate change mitigation potentials of biomass-based fuels in comparison with fossil energy. Specific questions and conditions which could be more suitable for each modelling choice are addressed. The attributional modelling is more suitable for national environmental taxation and emission labelling/accounting for import-export, while the consequential modelling is more appropriate for new production development and eco-design. Due to the potential environmental risks arising from the modelling limitations, the consideration of both the widely applied approaches could support decisions more comprehensively.

     

Notions on the Design and Use of an Ideal Regional or Global LCA Database

Goal, Scope and Background

More and more national and regional life cycle assessment (LCA) databases are being established satisfying the increasing demand on LCA in policy making (e.g. Integrated Product Policy, IPP) and in industry. In order to create harmonised datasets in such unified databases, a common understanding and common rules are required. This paper describes major requirements on the way towards an ideal national background LCA database in terms of co-operation, but also in terms of life cycle inventory analysis (LCI) and impact assessment (LCIA) methodology.

Methods

A classification of disputed methodological issues is made according to their consensus potential. In LCI, three main areas of dissent are identified where consensus seems hardly possible, namely system modelling (consequential versus attributional), allocation (including recycling) and reporting (transparency and progressiveness). In LCIA the time aspect is added to the well-known value judgements of the weighting step.

Results and Discussions

It is concluded that LCA methodology should rather allow for plurality than to urge harmonisation in any case. A series of questions is proposed to identify the most appropriate content of the LCA background database or the most appropriate LCI dataset. The questions help to identify the best suited approach in modelling the product system in general and multioutput and recycling processes in particular. They additionally help to clarify the position with regard to time preferences in LCIA. Intentionally, the answers to these questions are not attributed to particular goal and scope definitions, although some recommendations and clarifying explanations are provided.

Recommendations and Perspective

It is concluded that there is not one single ideal background database content. Value judgements are also present in LCI modelling and require pluralistic solutions; solutions possibly based on the same primary data. It is recommended to focus the methodological discussion on aspects where consensus is within reach, sensible and of added value for all parties.

     

Environmental and energy assessment of the substitution of chemical fertilizers for industrial wastes of ethanol production in sugarcane cultivation in Brazil

Purpose

Vinasse and filter cake are residues of bioethanol processing that are used to be recycled as fertilizers in sugarcane plantation. Studies related to the environmental dimension on this practice are concerned only with the effects on water and soil. The present study examines the systemic effects of replacing chemical fertilizers with vinasse and filter cake on the environmental performance of ethanol, via life cycle assessment (LCA).

Methods

The analysis was carried out by comparing various scenarios structured from two control variables: crop management techniques (manual and mechanized harvesting) and source of nutrients (for supplying the nutritional needs of sugarcane crops): chemical fertilizers, chemical fertilizers + vinasse, and chemical fertilizer + vinasse + filter cake. Impact assessment was carried out in terms of primary energy demand, climate change, terrestrial acidification, freshwater eutrophication, human toxicity, and terrestrial ecotoxicity. LCA has been applied according to both attributional and consequential perspectives. Moreover, a sensitivity analysis was performed in order to verify the effects of the varying amounts of nitrogen (N), phosphorus (P), and potassium (K) in the composition of vinasse on the results obtained for the impact profile.

Results and discussion

From the attributional LCA perspective, the most expressive contributions regarding primary energy demand occurred in terms of depletion of non-renewable fossils. Replacing chemical fertilizers with vinasse and filter cake was beneficial for the environmental performance of ethanol as it reduces climate change, terrestrial acidification, and human toxicity impacts and sustains freshwater eutrophication and terrestrial ecotoxicity unaltered in relation to scenarios using only fertilizers. In terms of consequential LCA, ethanol’s environmental performance is influenced by the inclusion of the production of calcium fluorite to compensate the hexafluorosilicic acid deficit occurring in conjunction to the decrease of phosphate fertilizer and is compensated by the benefits provided by the general reduced consumption of chemical fertilizers for most of the impact categories. The exception occurred for primary energy demand.

Conclusions

The reuse of residues from bioethanol production—vinasse and filter cake—as primary nutrient suppliers for the cultivation of sugarcane instead of chemical fertilizers is a valid practice that improves the environmental performance of ethanol, even if it is analyzed under a consequential LCA perspective. The transport of these inputs to the field must be managed, however, in order to minimize primary energy demand and climate change impacts.

     

Shift in the marginal supply of vegetable oil

Background, Aims and Scope

The consequential approach to system delimitation in LCA requires that consideration of the technologies and suppliers included are ‘marginal’, i.e. that they are actually affected by a change in demand. Furthermore, coproduct allocation must be avoided by system expansion. Vegetable oils constitute a significant product group included in many LCAs that are intended for use in decision support. This article argues that the vegetable oil market has faced major changes around the turn of the century. The aim of this study is to study the marginal supply of vegetable oil as it has shifted to palm oil and describe the product system of the new supply.

Methods

The methods for identification of marginal technologies and suppliers and for avoiding co-product allocation are based on the work of Weidema (2003). The marginal vegetable oil is identified on the basis of agricultural statistics on production volumes and prices. A co-product from palm oil production is palm kernel meal, which is used for fodder purposes where it has two main properties: protein and energy. When carrying out system expansion, these properties are taken into account.

Results

The major vegetable oils are soy oil, palm oil, rapeseed oil and sun oil. These oils are substitutable within the most common applications. Based on market trends, a shift from rapeseed oil to palm oil as the marginal vegetable oil is identified around the year 2000, when palm oil turns out to be the most competitive oil. It is recommended to regard palm oil and its dependent co-product palm kernel oil as the marginal vegetable oil. The analysis of the product system shows that the demand for 1 kg palm oil requires 4.49 kg FFB (oil palm fruit) and the displacement of 0.035 kg soybeans (marginal source of fodder protein) and 0.066 kg barley (marginal source of fodder energy).

Discussion

The identification of the marginal vegetable oil and the avoidance of co-product allocation by system expansion showed that several commodities may be affected when using the consequential approach. Hence, the product system for vegetable oils is relatively complex compared to traditional LCAs in which average technologies and suppliers are applied and in which co-product allocation is carried out by applying an allocation factor.

Conclusions

This article presents how the marginal vegetable oil can be identified and that co-product allocation between oils and meal can be avoided by system expansion, by considering the energy and protein content in the meal, which displaces a mix of the marginal sources of energy and protein for animal fodder (barley and soy meal, respectively).

Recommendations and Perspectives

The implication of a shift in the marginal vegetable oil is significant. Many LCAs on rapeseed oil have been conducted and are being used as decision support in the bio energy field. Thus, based on consequential LCA methodology, it is argued that these LCAs need to be revised, since they no longer focus on the oil actually affected.

     

Identifying marginal suppliers of construction materials: consistent modeling and sensitivity analysis on a Belgian case

Purpose

The identification of marginal suppliers is a key element of consequential LCA. This study investigates how systematically the identification of marginal suppliers can be performed across different products, while maintaining consistent modeling choices. Some products relevant for the Belgian construction sector are taken as a case study.

Methods

To gain insight in the current practice of identifying marginal suppliers, 30 recent studies have been reviewed. Based on the findings of the review, a method was proposed to identify geographical market boundaries from trade data and sensitive suppliers from production data. Both retrospective and prospective approaches to anticipate the future effect of a change in demand were taken into account. The method was applied to compute both a retrospective and a prospective marginal supplier’s mix per product. Finally, the effect of the modeling choices on the size of geographical market boundaries and marginal mixes was estimated via regression analysis.

Results and discussion

The forecasts and marginal mixes obtained matched with those from the existing literature, although clear differences in results are observed between the retrospective and prospective approach. Deviations from default assumptions in LCA were observed as well, such as large regional geographical markets for cement and aggregates instead of local ones. The statistical sensitivity analysis showed that identifying geographical market boundaries has the largest effect on the final marginal mix and that these markets are relative stable over time.

Conclusions

The proposed method and corresponding sensitivity analysis is an attempt to gain insight into the effect of modeling choices in the context of the identification of marginal suppliers for consequential LCA. It can in principle be applied to any product for which trade and production data are available. The proposed method helps to identify marginal mixes on a consistent and transparent way, to improve the robustness of the results in future consequential LCAs.

     

Life cycle assessment in the furniture industry: the case study of an office cabinet

Purpose

In an effort to reduce the environmental impacts of the furniture sector, this study aimed to diagnose the environmental performance of an office cabinet throughout its life cycle.

Methods

An attributional life cycle assessment (LCA) was used, based on the ISO 14044 Standard and ILCD Handbook. The scope of the study considered the entire supply chain, from cradle to grave, including the steps of pre-manufacturing, manufacturing, use, and post-use of the product. The impact assessment method was the International Reference Life Cycle Data System (ILCD) 2011 midpoint.

Results and discussion

The results identified that the most significant environmental impact of the furniture life cycle was due to the distances covered and production of the main raw material, wood medium-density particleboard (MDP). The evaluation of transport scenarios showed environmental tradeoffs for truck fuel switches and environmental gains for the distribution of MDP from closer suppliers by truck, as well as from current supplier by truck and ship in the major categories. Furthermore, evaluation of the office cabinet post-use options showed that reuse, recycling, or energy recovery from waste cause significant environmental gains in the major categories. Wooden furniture is a potential carbon sink if its life cycle does not emit more greenhouse gases than its materials can store. The impacts of substitution scenarios varied depending on the type of product avoided.

Conclusions

The LCA proved a powerful method to diagnose and manage environmental impacts in complex product systems. The sensitivity analysis showed that it is possible to reduce the environmental impacts and, at the same time, make the furniture industry increase its economic gains and net carbon stock in the anthroposphere.

     

Identifying marginal supplying countries of wood products via trade network analysis

Purpose

The consequential inventory modeling approach for life cycle assessment implies that an increase in the demand for a specific product is met by the marginal suppliers within the market. The identification of marginal suppliers is however complicated by difficulties in defining appropriate geographical market delimitations. In this study, an advanced system thinking approach is proposed to address this challenge in the identification of marginal supplying countries of wood products.

Methods

Groups of countries which represent geographical markets are identified from trade data by using a network analysis-based clustering technique. Within these markets, marginal supplying countries are selected based on positive historical increments. The analysis covers 12 different products and all countries in the world using trade data for the period 1998–2013.

Results and discussion

Global indices allow differentiating how product-specific trade networks are separated into communities and how interconnected these networks are. Large differences between products and minor differences between trade years are observed. Communities identified for each product tend to overlap with existing geographical regions and seem thus realistic. By combining this information with product-specific production increment rankings, marginal supplying countries of wood products were identified.

Conclusions

The identified geographical market delimitation is a key for proper consequential life cycle assessment (LCA) inventory modeling in areas such as timber-based construction and biomass-based energy production. The method can in principle be applied to any product for which trade network data are available and ideally should be accompanied by a detailed analysis of technological constrains within the identified supplying country.

     

Life cycle inventories of electricity generation and power supply in version 3 of the ecoinvent database—part II: electricity markets

Purpose

Representative, consistent and up-to-date life cycle inventories (LCI) of electricity supply are key elements of ecoinvent as an LCI background database since these are often among the determining factors with regard to life cycle assessment (LCA) results. ecoinvent version 3 (ev3) offers new LCI data of power supply (electricity markets) in 71 geographies. This article gives an overview of these electricity markets and discusses new ecoinvent features in the context of power supply.

Methods

The annual geography- and technology-specific electricity production for the year 2008 specifies the technology shares on the high-, medium- and low-voltage level electricity markets. Data are based on IEA statistics. Different voltage levels are linked by transformation activities. Region-specific electricity losses due to power transmission and voltage transformation are considered in the market and transformation activities. The majority of the 71 power markets are defined by national boundaries. The attributional ecoinvent system model in ev3 with linking to average current suppliers results in electricity markets supplied by all geography-specific power generation technologies and electricity imports, while the consequential system model generates markets only linked to unconstrained suppliers.

Results and discussion

The availability of LCI data for 71 electricity markets in ev3 covering 50 countries reduces the “Rest-of-the-World” electricity supply not covered by country- or region-specific inventories to 17 % for the year 2008. Specific power supply activities for all countries contributing more than 1 % to global electricity production are available. The electricity markets show large variations concerning contributions from specific technologies and energy carriers. Imports can substantially change the national/regional power mix, especially in small markets. Large differences can also be observed between the electricity markets in the attributional and the consequential database calculation. Region-specific total power losses between production on the high voltage level and consumer on the low voltage level are on the order of 2.5–23 %.

Conclusions

Electricity supply mixes (electricity markets) in the ecoinvent database have been updated and substantially extended for v3. Inventories for electricity supply in all globally important economies are available with geography-specific technology and market datasets which will contribute to increasing quality and reducing uncertainties in LCA studies worldwide and to allow more accurate estimation of environmental burdens from global production chains. Future work should focus on improving the details of country-specific data, implementation of more countries into the database, splitting of large countries into smaller regions and on developing a more sophisticated approach specifying country-specific electricity mixes in consequential system models.

     

Uncertainty in LCA case study due to allocation approaches and life cycle impact assessment methods

Purpose

Uncertainty is present in many forms in life cycle assessment (LCA). However, little attention has been paid to analyze the variability that methodological choices have on LCA outcomes. To address this variability, common practice is to conduct a sensitivity analysis, which is sometimes treated only at a qualitative level. Hence, the purpose of this paper was to evaluate the uncertainty and the sensitivity in the LCA of swine production due to two methodological choices: the allocation approach and the life cycle impact assessment (LCIA) method.

Methods

We used a comparative case study of swine production to address uncertainty due to methodological choices. First, scenario variation through a sensitivity analysis of the approaches used to address the multi-functionality problem was conducted for the main processes of the system product, followed by an impact assessment using five LCIA methods at the midpoint level. The results from the sensitivity analysis were used to generate 10,000 independent simulations using the Monte Carlo method and then compared using comparison indicators in histogram graphics.

Results and discussion

Regardless of the differences between the absolute values of the LCA obtained due to the allocation approach and LCIA methods used, the overall ranking of scenarios did not change. The use of the substitution method to address the multi-functional processes in swine production showed the highest values for almost all of the impact categories, except for freshwater ecotoxicity; therefore, this method introduced the greater variations into our analysis. Regarding the variation of the LCIA method, for acidification, eutrophication, and freshwater ecotoxicity, the results were very sensitive. The uncertainty analysis with the Monte Carlo simulations showed a wide range of results and an almost equal probability of all the scenarios be the preferable option to decrease the impacts on acidification, eutrophication, and freshwater ecotoxicity. Considering the aggregate result variation across allocation approaches and LCIA methods, the uncertainty is too high to identify a statistically significant alternative.

Conclusions

The uncertainty analysis showed that performing only a sensitivity analysis could mislead the decision-maker with respect to LCA results; our analysis with the Monte Carlo simulation indicates no significant difference between the alternatives compared. Although the uncertainty in the LCA outcomes could not be decreased due to the wide range of possible results, to some extent, the uncertainty analysis can lead to a less uncertain decision-making by demonstrating the uncertainties between the compared alternatives.

     

Evaluating the carbon footprint of the cork sector with a dynamic approach including biogenic carbon flows

Purpose

The aim of the present study is to assess the influence of two different attributional life cycle assessment (LCA) approaches, namely static LCA (sLCA) and dynamic LCA (dLCA), through their application to the calculation of the carbon footprint (CF) of the entire cork sector in Portugal. The effect of including biogenic carbon sequestration and emissions is considered as well.

Methods

sLCA is often described as a static tool since all the emissions are accounted for as if occurring at the same time which may not be the case in reality for greenhouse gases. In contrast, dLCA aims to evaluate the impact of life cycle greenhouse gas emissions on radiative forcing considering the specific moment when these emissions occur.

Results and discussion

The results show that the total CF of the cork sector differs depending on the approach and time horizon chosen. However, the greater it is the time horizon chosen, the smaller the difference between the CF results of the two approaches. Additionally, the inclusion of biogenic carbon sequestration and emissions also influences significantly the CF result. The cork sector is considered a net carbon source when biogenic carbon is excluded from the calculations and a net carbon sink when biogenic carbon is included in the calculations since more carbon is sequestered than emitted along the sector.

Conclusions

dLCA allows an overview of greenhouse gas emissions along the time. This is an advantage as it allows to identify and plan different management approaches for the cork sector. Even though dLCA is a more realistic approach, it is a more time-consuming and complex approach for long life cycles. The choice of time horizon was found to be another important aspect for CF assessment.

     

The EcoSpold 2 format—why a new format?

Purpose

This paper introduces the new EcoSpold data format for life cycle inventory (LCI).

Methods

A short historical retrospect on data formats in the life cycle assessment (LCA) field is given. The guiding principles for the revision and implementation are explained. Some technical basics of the data format are described, and changes to the previous data format are explained.

Results

The EcoSpold 2 data format caters for new requirements that have arisen in the LCA field in recent years.

Conclusions

The new data format is the basis for the Ecoinvent v3 database, but since it is an open data format, it is expected to be adopted by other LCI databases. Several new concepts used in the new EcoSpold 2 data format open the way for new possibilities for the LCA practitioners and to expand the application of the datasets in other fields beyond LCA (e.g., Material Flow Analysis, Energy Balancing).

     

Bridge processes: a solution for LCI datasets independent of background databases

Introduction

New platforms are emerging that enable more data providers to publish life cycle inventory data.

Background

Providing datasets that are not complete LCA models results in fragments that are difficult for practitioners to integrate and use for LCA modeling. Additionally, when proxies are used to provide a technosphere input to a process that was not originally intended by the process authors, in most LCA software, this requires modifying the original process.

Results

The use of a bridge process, which is a process created to link two existing processes, is proposed as a solution.

Discussion

Benefits to bridge processes include increasing model transparency, facilitating dataset sharing and integration without compromising original dataset integrity and independence, providing a structure with which to make the data quality associated with process linkages explicit, and increasing model flexibility in the case that multiple bridges are provided. A drawback is that they add additional processes to existing LCA models which will increase their size.

Conclusions

Bridge processes can be an enabler in allowing users to integrate new datasets without modifying them to link to background databases or other processes they have available. They may not be the ideal long-term solution but provide a solution that works within the existing LCA data model.