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N. D. Mortimer
N. D. Mortimer
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The scene is set for understanding the potential role of life cycle assessment as a metric for circular economy in Chapter 1 of this book, which introduces the theories and tools for assessing the impact of human activities on resources and the environment. The increasing magnitude of these impacts is traced to the growth of the human population and the continued industrialisation of human society. Ongoing responses, largely based on economic, social and environmental sustainability, are summarised, with those concluding the need for circular economy as a means of extending resources and reducing environmental damage, being highlighted. The importance of quantifying progress with the transition from linear to circular economy is clearly established. The relevance of life cycle assessment as a suitable tool for such quantification is explored through its historical development and its links with theories concerning planetary carrying capacity and boundaries, industrial ecology and cleaner production. Whilst demonstrating such relevance, notable methodological challenges are raised regarding the consistent and transparent application of full life cycle assessment, which covers all resource and environmental impacts, to circular economy.

The foundations for appreciating the fundamental aspects of circular economy are laid in Chapter 2. The negative impacts of existing linear economy are contrasted with the potential benefits of circular economy. However, despite these well-known attractions, the current slow progress with implementing circular economy is illustrated. Although the many definitions of circular economy are acknowledged, the most helpful are recognised as those that apply practical perspectives to maximising utility, whilst creating value from the cycling of resources. Key principles are identified, which entail adopting cradle-to-cradle approaches in the provision of products and services, taking into account loops in what are referred to as technical and biological materials. Important aspects of circular economy are summarised for the specific industries addressed by case studies in subsequent chapters. Tools for assessing circular economy are introduced, including materials flow analysis, environmental extended input-output analysis and life cycle assessment. It is noted that, in order to provide adequate evaluation of circular economy, such tools must often be used in combination with careful consideration of their contexts, systems boundaries, metrics, indicators, documented data sources and methodological limitations. Three principles are described for business models, which are intended to untap opportunities for value creation from circular economy. Stages for implementing circular economy in businesses are summarised and examples of policy intervention in the European Union and China are provided. The chapter concludes by outlining some of the conditions that will promote and challenge the widespread adoption of circular economy.

An essential introduction to the application of life cycle assessment in the implementation of circular economy is given in Chapter 3. To those who do not work with or encounter life cycle assessment on a regular basis, this technique can sometimes seem to be an impenetrable specialism. This may be largely due to the use of its own dedicated terminology. It is, of course, important to understand the specific terms that are used in life cycle assessment to appreciate the meaning of its results. However, it is helpful to appreciate that life cycle assessment is based on regarding any individual activity or collection of activities as a system in which there are flows of inputs and outputs. Once such systems thinking is embraced and understood, much of the apparent complexities of life cycle assessment should become more accessible. Amongst the four distinct stages of any life cycle assessment exercise, it can be argued that the most crucial is the first. This is because, as well as identifying the system under investigation, this first stage should involve specifying, in a clear, coherent and comprehensive manner, the purpose of the investigation which, in turn, determines all aspects of the methods of calculation and analysis subsequently used. In doing so, this ensures that the actual results answer the particular question being asked. Subsequent stages consist of producing reliable estimates of the inputs and outputs of the system, translating inputs and outputs into indicators of impact, and, finally, interpreting results for communication and eventual use in decision-making. An extensive summary of the variety of international and national standards and guidelines for the life cycle assessment of products and organisations is provided. Possible extension of life cycle assessment from resource and environmental considerations to economic and social concerns is outlined. Practical challenges in applying life cycle assessment to circular economy are addressed, especially in relation to potential trade-offs between environmental impacts and materials circularity.

Both concrete and steel are very important components in the construction of buildings and infrastructure. They have contrasting features, as explained in Chapter 4, which provides a life cycle assessment case study of two designs for an office building in France: one constructed mainly in concrete (with reinforced steel) and one mainly in steel (with concrete foundations and floors). By unit weight, the manufacture of concrete generally has lower impacts, particularly in terms of fossil fuel consumption and greenhouse gas emissions, than the production of steel. However, in the different designs, a lower weight of steel is required relative to the weight of concrete. The combination of these two factors is shown to give a slight advantage for the steel design over the concrete design. As well as the construction phase, the use phase and end-of-life phase, including the potential for materials recovery and recycling, of these designs are evaluated in the case study. Both designs have the same ongoing energy demands and satisfy the same environmental regulations, and, as is typical currently, the use phase dominates the magnitude of impacts in the case study. The role of Environmental Certification of Buildings is considered, especially in relation to reducing operational energy demands. Future widespread deployment of passive, near zero and net zero energy building designs is expected to reduce the importance of the use phase, thereby elevating the relevance of the construction phase in the life cycle assessment of buildings. Hence, Environmental Product Declarations, which incorporate information from life cycle assessment of specific building components, should become increasingly important as a means to reduce the impacts of the construction phase. However, the limitations of current approaches that are unable to accommodate other concerns, including social value, are emphasised.

The construction industry will play an important part in establishing the infrastructure necessary for the transition to the net zero carbon economy. Hence, it is necessary to determine the magnitude of possible reductions in the greenhouse gas emissions associated with the main materials, such as cement and steel, consumed by this industry. The use of life cycle assessment in evaluating greenhouse gas emissions savings in the production of cement, aggregates and concrete is explored, using case studies from Hong Kong, in Chapter 5. Significant potential for reducing greenhouse gas emissions, along with savings in non-renewable energy consumption, are reported by adopting the principles of circular economy in the relevant production processes. This involves considering alternatives to clinker based on limestone, sand and iron ore, in the form of fly ash and waste glass powder, alternative fuel to coal, in the form of co-fired pellets made from waste wood, alternatives to natural aggregates, in the form of construction and demolition wastes and waste glass sand, and alternative supplementary cementitious materials, in the form of fly ash, granulated blast furnace slag and silica fume. The importance of avoiding landfilling, as a particularly local concern, is emphasised and taken into account in these life cycle assessments. It is recognised that realisation of estimated benefits by the construction industry is only developing slowly due to the lack of necessary methodologies, guidelines and indicators.

Chapter 6 gives a closer look at the application of life cycle assessment to the use of waste glass powder as a supplementary cementitious material in concrete. This is achieved by means of a case study involving the provision of a pedestrian bridge deck over a 100-year period in Canada. As such, the use of waste glass powder is an example of open-loop circular economy and life cycle assessment is adopted to derive indicators of resource and environmental impacts of new concrete mixes relative to conventional concrete. In generating appropriate results for meaningful comparison, the need to specify the essential details of life cycle assessment carefully is clearly emphasised and suitably demonstrated. In particular, it is established that a whole range of environmental impacts, and not just global warming potential, must be taken into consideration to avoid possible trade-offs between different burdens. Additionally, locational and technological variations may have to be addressed. Furthermore, the choice of any co-product allocation must be relevant and properly justified. Most critically, the correct functional unit must be selected. In this specific case study, in which different concrete mixes have different properties of strength and durability, the lifespan of the bridge deck, rather than the volume of concrete or the structure of an individual bridge, becomes an important element of the functional unit. This has a fundamental influence on the results, which are tested for robustness using sensitivity and uncertainty analyses, allowing subsequent outcomes to be qualified accordingly.

Chapter 7 focuses on the application of life cycle assessment to specific polymer materials and packaging, in the form of food trays, which incorporate starch derived from biomass feedstocks. Two case studies are reported, which demonstrate the need to consider quite a large variety of factors in the life cycle assessment of new materials and products. This is mainly because polymers produced from both biomass feedstocks and petrochemicals have the potential to exhibit circular economy regarding possible recycling of biogenic and fossil carbon, respectively. It is shown that whether such potential can be achieved depends crucially on the recyclability of the packaging, which can affect the practical choice of end-of-life treatment. At present, some biopolymers cannot be recycled, unlike a number of conventional plastics derived from petrochemicals. This can tip the balance of comparative environmental benefits away from certain biopolymers and towards their established petrochemical alternatives. However, other factors are capable of swinging the balance back the other way. In the case studies examined, the particular type of biomass feedstock used to produce biopolymers and the specific technique for forming packaging trays from biopolymers are found to exert important influences on the comparative outcomes from life cycle assessment.

Both the complexity and rapidly evolving nature of the textiles industry present important difficulties for its successful transition to circular economy. These difficulties are compounded by increased pre- and post-consumer waste generation due to traditionally short product lifetimes, which are being exacerbated by the growth of fast fashion. Nevertheless, such transition is regarded as a possible solution for an industry that can be viewed as unsustainable, not only environmentally but also economically. Chapter 8 demonstrates the complexity of this industry by reviewing the wide variety of processes involved in producing textiles from natural and synthetic fibres. The general results of life cycle assessment studies are summarised to present a picture of the daunting array of resource and environmental impacts from textile production, use and end-of-life phases. A specific case study is used to demonstrate the practical work involved in determining the impacts of polyethylene terephthalate yarn production in Turkey. The role of life cycle assessment is emphasised as a means of providing the necessary information for environmental performance labels which can initiate and maintain wider application of circular economy to textiles.

Processing of a range of different biomass feedstocks in biorefineries provides the means to create many different chemicals and/or fuels. If these chemicals, in particular, can be converted into plastics, which are equivalent to those currently produced from fossil fuels, an intriguing window of opportunity is opened for establishing a circular economy in biogenic carbon, which will be needed by a world tackling global climate change seriously within the short timescale to 2050. The possibility of achieving this is investigated in Chapter 9, which adopts inventory analysis from life cycle assessment to determine the annual mass balance of biogenic carbon between global sources of relevant biomass feedstocks and their potential conversion into chemicals and fuels in biorefineries. Very promising results are reported, especially for chemicals. However, caution is also noted regarding the practicalities of realising such promise. Specifically, further development is required to design bioplastics with use and end-of-life phases similar to those of existing products derived from petrochemicals, so that loops can be closed through present waste management practices. Additionally, further research is needed to exploit all the biogenic carbon components available in biomass feedstocks and to resolve the currently unfavourable economics of future biorefineries.

There is a well-established focus on the resource and environmental impacts of packaging, which is mainly due to its routine visibility to almost all members of society. This has resulted in a long history of applying life cycle assessment to packaging and its potential circular economy. Hence, Chapter 10 is able to draw on an extensive body of literature in the form of case studies covering many types of packaging from across the world. This provides the basis to identify key issues and challenges associated with the application of life cycle assessment to the circular economy of packaging. In particular, it is apparent that there is ongoing debate about the definition of appropriate functional units and the establishment of suitable systems boundaries. Packaging may have more than one function since it is not only an outer layer to a given product but is also a potential source of recyclable material. Repeated recycling of packaging materials with possible degradation introduces the need to consider temporal as well as spatial systems boundaries especially in dynamic rather than static circular economies. Using numerous examples, it is explained that these and other matters are not simply methodological problems for life cycle assessment practitioners. This is because effective means are required to enable any comparative resource and environmental benefits from the circular economy of packaging identified by life cycle assessment to be translated into product design, to influence business organisation and to be communicated to consumers.

Valorisation, or the re-classification and transformation of previously regarded wastes into useful resources, is the main subject of Chapter 11, which focuses on agricultural crop production. In its current form, agriculture is viewed as unsustainable due to its use of non-renewable energy and minerals, and its unacceptable environmental impacts. Improvements in efficiency are needed by adopting the principles of circular bioeconomy, which involves turning former wastes into more valuable co-products and by-products. Life cycle assessment can assist this process by evaluating the options available and by identifying those which result in the lowest resource and environmental impacts and/or the greatest economic and social benefits. It is proposed that this requires an approach based on different levels of detail in life cycle assessment, which reflects the level of maturity of the technologies needed to transform agricultural wastes into suitable feedstocks. The potential of this approach is demonstrated using five case studies from America, Asia and Europe, which exhibit features of linear systems, and open- and closed-loop circular systems. General principles are drawn for applying the circular economy to food production systems. Limitations are also identified with the application of life cycle assessment which is currently unable to capture the restoration and regeneration of natural systems.

Some of the complexities in evaluating the impacts of activities on a global scale illustrated in Chapter 12, which considers livestock production. The main challenges are identified as food security and climate change with a growing global population increasing the demand for meat production. The context of livestock production and its impacts are illustrated by case studies based on beef production in Brazil and dairy production in Kenya. The many different sources of greenhouse gas emissions that have to be taken into account for both local and global systems modelling are outlined. These sources include enteric emissions from the animals themselves, emissions from their manure, net carbon dioxide emissions or absorption from soil and biomass caused by land use changes, and greenhouse gas emissions associated with the use of fossil fuels in the processes involved in producing and delivering food for eventual consumption. Since competition for land for different uses is important, such modelling must accommodate not only livestock production but also alternatives such as crop and bioenergy production. Additionally, the behaviour and preferences of consumers must be addressed. Variations in these and other factors result in different outcomes, as exemplified by estimated global greenhouse gas emissions from livestock production up to 2050. In particular, these estimates are shown to be influenced most strongly by levels of daily meat consumption by individuals, the choice of type of meat and livestock yields.

Bioenergy, as a potentially renewable form of energy based on the use of biomass as a feedstock, can be regarded as an example of the circular economy applied to the recycling of biogenic carbon. In the case of fuels made from such feedstocks, this is because the carbon dioxide released during their combustion will have been absorbed during the original growth of the biomass. However, this does not necessarily mean that, in practice, bioenergy is carbon neutral. There are many possible sources of greenhouse gases that have to be taken into account when considering the production and use of biofuels. Life cycle assessment is ideally suited to evaluating the relevance and magnitude of these sources in the essentially closed loop circular biogenic economy of bioenergy systems. The synergy of the methodology of life cycle assessment and the principles of circular economy to maximise resource efficiency and minimise environmental impacts is demonstrated in Chapter 13, which presents five case studies of biofuel production and use. Overall, these case studies illustrate the importance of determining significant negative and positive factors on the calculation of total greenhouse gas emissions. Negative factors include greenhouse gas emissions from the fossil fuels, fertilisers, chemicals and other products used in the provision and conversion of biomass feedstocks, leakages due to the burning of agricultural wastes, direct land use change which occurs when land is converted to biomass feedstock cultivation, and indirect land use change which might arise when cultivation of a biomass feedstock displaces an existing crop to another location. Positive factors include the use of agricultural residues as biomass feedstock and the co-production of other outputs from the biomass conversion process, which substitute for products previously made from and/or with fossil fuels.

The necessarily rapid transition from current energy systems based on fossil fuels to those depending on renewable energy technologies and their supporting storage systems will have a significant effect on the demand for relevant materials. In addressing this important consideration, Chapter 14 shows clearly that transforming energy systems from fossil fuels to renewables will not so much alleviate concerns over depletion, but will rather switch attention from resources of fossil fuels to the availability of metals. This is achieved by estimating the metal requirements up to 2050 of five energy scenarios based on assumptions about the mix of different renewable energy technologies and battery storage options. Two methods are used to derive depletion scores in terms of life cycle impact characterisation. This enables critical metals to be identified and possible options for avoiding problems to be outlined. Such options include the possible use of alternative storage methods, the direct substitution of critical metals, and the potential for metal recovery and recycling by introducing circular economy to the life cycle of renewable energy systems. Additionally, it is noted that competition for other uses of critical metals is a relevant factor that has to be taken into account.

Beyond the details of specific case studies and their particular conclusions there is a wider debate about the concept of circular economy and the application of life cycle assessment. This necessary debate, which challenges any possible nebulous thinking over the claimed benefits of circular economy and their apparently precise quantification by life cycle assessment, is thought-provokingly addressed in Chapter 15. Areas of fundamental problems are identified with reference to strong versus weak sustainability, relative versus absolute sustainability, incorporation or separation of humans and the environment, and negative and positive interpretations of sustainability. Unless properly resolved, some of the underlying issues that are revealed have the potential to undermine the practical realisation of any actual environmental, economic and social benefits from circular economy. Such resolution recognises that, at this particularly critical time, the most appropriate concepts and tools must be adopted and adapted to support serious decision-making. It is argued that life cycle assessment, as a tool to assist implementation of the concept of circular economy, needs to evaluate absolute, rather than relative, sustainability with regard to unbreachable planetary boundaries as part of its impact assessment. Additionally, economic aspects need to be incorporated into life cycle assessment to demonstrate whether circular economy has economic benefits and, if not, what alternative economic systems are required to ensure they can be realised. Ideally, an encompassing relationship is envisaged between the inspiring vision of circular economy and the thorough testing of its environmental and economic outcomes by life cycle assessment.

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