By John Mulrow & Victoria Santos
One of the great battles of modern scientific understanding was fought in the 17th century among “chymists” who claimed to be deciphering the composition and workings of nature. Many of these chymists – or alchemists as we now call them – believed that everything was composed of one or more of four elements: air, water, fire and earth. And indeed, alchemists could demonstrate that the burning of wood yielded all four, in the form of rising smoke, bubbling vapors, flames, and ash. This was one of their most common experiments. But in 1661 Robert Boyle, a young Oxford scientist, published The Sceptical Chymist, a work which threw the alchemists’ definitions and lines of inquiry into question and helped to birth the modern scientific method.
Boyle urged chymists to seek deeper explanations for physical transformations beyond the four elements, writing that alchemists’ explanations were too vague to yield valuable knowledge. They “write darkly, not because they think their notions too precious to be explained, but because they fear that if they were explained, men would discern that they are far from being precious”[i] Boyle put his skepticism to use, developing repeatable laboratory methods for investigating the nature of the “elements” and he is most well-known today for developing Boyle’s Law, which describes the relationship between the pressure and volume of a gas.
This little history of Robert Boyle and the alchemists provides some framework for considering the recently-published issue of the Journal of Industrial Ecology titled, “Exploring the Circular Economy.” In it, academics and practitioners alike pick apart the Circular Economy buzz, its history, and its underlying theory. Like Boyle, the authors in this issue have largely focused on the Circular Economy’s main “elements” – as they are commonly stated in popular and corporate literature – but point out that these elements are far too simplistic to yield the global sustainability results that motivate CE practitioners. Some authors even claim that this simplicity risks moving us away from desired outcomes.
The issue contains 25 articles, written mostly by academics based in Europe, the United States, Australia, and China (in order of frequency), with some industry consultants, non-profit, government, and business representation. Many of the authors have been promoters of circular economy thinking, or have been researching material flows and innovative solid waste management systems for many years. Nevertheless, they are skeptical circular economists, in the spirit of Boyle, with many suggestions for improving the concept going forward.
The summary of the issue that follows is also a virtual tour of circular economy definitions and current directions. The authors discuss and derive new definitions of “circularity.” They cover fundamental determinants of material lifespan, such as economic demand, thermodynamics, product design, and durability. There is a large focus on aspects of the circular economy’s “validity test” – the challenging territory of rebound effects, psychology, and social dynamics that must be traversed in the service of global sustainability. Finally, we attempt to connect the dots along the way, summarizing solutions and deriving the conclusion that, in order to head toward true sustainability, material lifetimes must grow (slowing loops) and total material dependency must decline (shrinking loops) as more material loops are “closed” through CE initiatives. We argue that these are key checkpoints on the journey beyond simplistic alchemy and toward robust validity.
Elements of Circularity
The general purpose of the CE concept is to bring into focus the transformation of a linear economy to a circular economy. The classic image here shows a single arrow connecting take, make, use, and dispose, implying that materials are extracted and flow through the economy once, then are left behind at “dispose” with no further thought to their usefulness. In the circular economy vision, this straight arrow becomes a circle, bending back upon itself and implying that materials can be reclaimed and put to use again and again. Many of the special issue’s authors, in defining the central theme of the CE, referenced the Ellen MacArthur Foundation and the “butterfly diagrams” they have developed to demonstrate the real or potential flow of byproduct materials back into production phases. The EMF has funded major publications on CE in recent years, fueling widespread popularity of the CE transformation, especially among the business community. These publications, or the EMF website, were referenced 82 times among 20 of the 25 articles in this issue.
Table 1: Key terms discussed throughout Exploring the Circular Economy, including the number of times a term appears in the issue and the number of articles in which it appears. Word count analysis included article abstracts, main body and references.
|Limits / Boundaries||27||55|
|Ellen MacArthur (Foundation)||20||82|
In analyzing the impact of linear-to-circular framework, researchers ask: What kinds of solutions, or lines of questioning, are motivated by the concept? Nancy Bocken and her team mined ten years’ worth of press releases from 101 companies listed on the Standard and Poor’s 500 stock index.[ii] Using text mining, they analyzed the number of times a CE-related concept was mentioned in the more than 90,000 press releases. Two words – maintenance and recycl(-e and –ing) – were the clear winners, with 6,850 and 4,326 total mentions, respectively. The next six were refurbish (392), waste management (169), compost (134), reduce waste (126), closed-loop (96) and zero waste (96). Notably, the term “circular economy” was absent from all 90,000 documents examined by Bocken’s research team.
Several authors put forward methodologies for measuring the “circularity” of a product. Jonathan Cullen looked at a set of energy-intensive materials and devised a Circularity Index, or CI, (Table 1) based on industry data for recycling volumes and recycling energy requirements.[iii] The CI scores for Steel, Concrete, Plastic, Paper and Aluminum are listed, with 0 being no circularity and 1 being perfect circularity (a thermodynamically impossible score). Aluminum, the top scorer, benefits from the massive energy savings involved in substituting recovered aluminum for raw material – recovery requires just 4% of the energy required for primary production. But Aluminum still scores only 0.2 on the Circularity Index, given that recovered material meets only 21% of global Aluminum demand.
Table 2. Circularity Index (CI) of Selected Materials. Adapted from Cullen 2017
|Energy-Intensive Materials||Circularity Index
This circularity measure communicates a sense of the product’s circularity based on production costs. Like Cullen, Linder’s team shows that a perfect circularity score is almost unimaginable, as repurposing inherently requires additional material and energy inputs at a cost. Here, the skeptical circular economists are reminding us that there is no free lunch. An indefinite circularity is not possible; not within the laws of thermodynamics. And this is precisely why Cullen’s article is titled, “Circular Economy: Theoretical Benchmark or Perpetual Motion Machine?” in reference to the many engineers who tried to patent machines that supposedly produced motive power with no external fuel source. This was before 1911 when the US Patent Office stopped accepting applications for perpetual motion machines. Has enough time passed that we are again vulnerable to promises of free and indefinite circularity?
Marcel den Hollander and colleagues ask how product design can still aim for the circular economy’s aspirational goals of keeping materials in use for as long as possible, minimizing the need for new extraction and production activities.[v] Their proposed product design framework is based on the Inertia Principle initially proposed by long-time circularity thinker Walter Stahel. It says:
Do not repair what is not broken, do not remanufacture something that can be repaired, do not recycle a product that can be remanufactured. Replace or treat only the smallest possible part in order to maintain the existing economic value of the technical system. [vi]
Hollander and team’s design guidance includes the usual list of “R’s” such as repair, refurbish and remanufacture, but their most hard-hitting recommendation is to “resist obsolescence”, which designers can do by creating products that are both physically and emotionally durable. The researches note that this latter concept of emotional durability has not gotten the attention it deserves. How and why we become attached, and eventually detached, to our products is a complex topic that cannot be entirely controlled by a product designer. However, circular economists are called to note that the physical durability, or circularity, of a product can be almost meaningless in the face of a culture adapted to product novelty and high turnover in possessions.
In asking what exactly the transformation from a linear economy to a circular economy looks like, researchers have uncovered plenty of factors that aren’t quite as simple as bending an arrow into a circle and dreaming of infinitely useful material flow. If CE is to contribute to the global sustainability effort, it must show real credentials on reducing total material demand at a planetary-scale. These circularity and design principles, armed with reproducible methodology, provide just such a reality check on the circular economy, and through them we see that CE cannot simply be a matter of “closing loops” but also of shrinking material throughput and changing cultures.
The Validity Challenge
Resource Life-Extending Strategies, or RLES’s, is the term Blomsma and Brennan use to describe the array of concepts developed through a long history of industrial and environmental thinking that the CE aims to join together into a single “umbrella concept.”[vii] Much as Boyle wrote of the evolution in alchemical methods and frameworks, Blomsma and Brennan recount the ways in which RLES concepts came about and how writers and researchers have built on each other’s ideas over the years.
They classify most of this history as either preamble or excitement, noting in their timeline that the coherence of the CE concept has yet to be determined. The Circular Economy, they say, is just entering its validity challenge phase, as:
An umbrella concept usually sees its validity challenged when attempts at operationalizing the concept bring to the surface unresolved issues regarding its definition and assessment. A plurality of definitions, a lack of tools, and the existence of different indicators surface during this stage, raising questions regarding the nature of the binding capacity of the umbrella concept.
Blomsma and Brennan call on their fellow industrial ecologists to tackle the validity challenge head-on. They make the point that the tools of industrial ecology – life cycle assessment, material flow analysis, and input-output models – have done the job of identifying what circular economy means, and must now turn to the how. Their biggest recommendation for making this leap is to incorporate social dynamics into the literature, via partnerships with “law, ethics, economics, system dynamics, and sociology and organizational studies” communities.
Other missing variables in the popular conception of CE that were explored in this special issue include the rebound effect and the decoupling of economic well-being from environmental impact. The rebound effect shows up in four articles in this issue and is a growing concern that circular economy researchers and practitioners cannot continue to ignore. A simple thought exercise illustrates this effect. Think of any resource or energy efficiency initiative you have heard about promoting a “win-win” for the environment and the economy. The logic goes: Make a process or product more efficient and both resource use and costs come down. But, what actually happens in the real world when costs come down? Depending on the good, and the time scale, total consumption may actually rise in the face of lower costs. And indeed, when we look back at the fuel efficiency and manufacturing productivity gains of recent history, they tend to be linked to an overall increase in resource use and environmental impact. The fuel economy of a Model T Ford averaged 17 miles per gallon in 1908, and in 2014 the average passenger vehicle in the US ran at 22 miles per gallon.[viii],[ix] Obviously, today’s motor technology is far more sophisticated than the old days, but all the efficiency gains have gone into car features and durability – the reason modern mpg looks unimpressively similar to the Model T’s. Furthermore, the usability features gained from better motor technology has made cars more attractive and affordable to use, driving up total fuel consumption over time.
Zink and Geyer, in their article, “Circular Economy Rebound,” describe a criteria for testing the rebound effect. They ask, does total production rise as a result of a given CE intervention?[x] If so, then you have rebound. This simple question puts many growth-oriented CE scenarios into perspective. If the point of the Circular Economy is to enable increased material throughput, in the form of increased production, then it cannot credibly claim to be reducing impacts at the planetary scale. The authors also mention potential rebound effects for virtualization and product recovery, two commonly promoted CE interventions. In their words,
Video-on-demand, which is virtualization of media delivery, often has lower per-use impacts than physical video delivery… however, video-on-demand has also increased consumption of video content. Recoverable rocketry, such as that being pioneered by SpaceX and Virgin Galactic, has lower per-launch and per-rocket material and energy requirements, but also makes rocketry cheaper and therefore may increase the number of launches.
These seem like obvious conclusions. Isn’t the whole point of technology to make things easier and cheaper for more people around the world? Perhaps, but if the stability of the Earth system for all 7.5 billion folks on the planet is a concern, then the global material impact of technological progress cannot be ignored. This is why many CE researchers have focused on the idea of decoupling achievements in well-being from their resource requirements. In other words, the goal is to grow well-being without growing impact.
Tisserant et al. point out that relative decoupling of raw material use and economic growth has occurred in most developed economies.[xi],[xii] However, relative decoupling just means that raw material use is growing at a slower rate than the country’s gross domestic product (GDP). Absolute decoupling – when the two growth rates become uncorrelated – would be a more robust goal if planetary limits are of concern. Tisserant and colleagues’ article on the circularity of global solid waste management asks how economic size and consumption are related to the “waste footprint” of nations, i.e. material generated, reused, recycled or landfilled. By crediting waste generation to final consumers, rather than the territory in which the waste was generated, they show that waste footprints are closely correlated with personal affluence rather than prevalent waste handling systems. This means, for example in the United States, that our recycling promotion initiatives weigh far less heavily on global environmental outcomes than would initiatives to reduce consumption.
The Circular Economy’s validity challenge requires a serious confrontation with long-standing assumptions about “green” and sustainable initiatives. As we have seen, a deeper examination shows that some assumptions – especially concerning efficiency and decoupling – are very limited, if not backwards. So how do we turn these lessons into enlightened solutions, preserving the inspirational power of the Circular Economy? We turn to this question next.
It may seem, up to now, that this entire issue of the Journal of Industrial Ecology was dedicated to dashing CE advocates’ hopes and dreams for a healthy planet. This can often feel like the case in academia where there is a constant need to refine, or sharpen, terms and methods. Buzzwords, especially, do not survive the academic fray with ease. Luckily, this sharpening process can yield more powerful tools for getting after hopes and dreams in a more honest and operable fashion. Here are some of the tools and solutions presented by the authors:
Enable circularity through design. Several authors confront circularity through the lens of design principles. Baxter et al. propose the term contaminated interaction to convey an important circularity obstacle to consider when designing products and systems.[xiii] Contaminated interaction describes the fact that knowledge of an object’s past use changes its value, or even its function, for the current user. This change can be positive (think of the value of celebrity-autographed items) or negative (think of second-hand underwear). But as Baxter and team point out, contaminated interaction “originates from an individual’s perception of an object, is socially constructed, and guides how the object is interacted with.” The need for cultural shift – involving the perception of used goods – is cited as a route to enabling durability, a point also made by Hollander et al. Baxter’s article suggests that designers should work on ways of ensuring that objects can be transferred between users while maintaining perceived value. Durability and customizability are two design features highlighted.
Other design guidance comes from Peiró et al. who suggest five strategies that enable disassembly and/or easy repair of a product.[xiv] These strategies, summarized, are: (1) Use modular construction, (2 & 3) Minimize the number of disassembly operations and connections, (4) Use tools as simple and generic as possible, (5) Make connectors durable and reusable.
Find solutions before and after production. The application of CE principles to mining and the built environment provide viewpoints outside of the typical realm of products, production, byproducts, and waste management. Ness and Xing encourage CE practitioners to think about the embodied energy and materials of existing building stock, proposing a methodology that is focused on long-term management of buildings and their potential uses and re-uses.[xv] They make a special point about the human labor intensity and ingenuity required for continual adaptive reuse of buildings, which makes the built environment less vulnerable to automation, as well as a potential job creator.
Lèbre and colleagues also focus on longevity, and prolonging/slowing of operations, but in the context of mining sites.[xvi] This is an eye-opening perspective for the CE practitioner who is typically concerned with the method and rate of material usage, only after extraction. But, as Lèbre’s research shows, there are many opportunities to increase both efficiency and durability at mining sites.
Pursue global policy cooperation. Some important CE background not yet mentioned is the fact that both China and the European Union have official policies that reference the Circular Economy as a basis for state-sponsored economic and environmental programs and regulation. McDowall et al. examine their CE-related policies, considering similarities and differences.[xvii] They choose two quotes from official government documents as representative of this comparison:
Ultimately, the authors suggest that the two governments should engage in “mutual learning” going forward, sharing best practices between themselves and with the rest of the world.
Implement locally-tailored solutions. The term “local” appears 77 times and in 15 articles throughout the special issue (see Appendix A), alluding to a link between circularity and the geographic scale and scope of analysis. In an article by John Mulrow (also an author of this review) and other Chicago-based researchers, a framework is outlined for “Industrial Symbiosis at the Facility Scale.”[xviii] Industrial Symbiosis (IS) describes the exchange of materials among firms so that the byproducts of some businesses become inputs for others. The facility-scale IS framework accounts for the fact that co-located businesses exchange material byproducts, but they also exchange and share other forms of capital such as building amenities, client networks, product innovation costs, and marketing and reputation. The hyper-locality of such a scheme provides both social and geographic proximity that can be a powerful tool for the kind of culture-shifting changes called for by other authors.
Use social principles to unlock circularity. Vincent Moreau and his team provide an apt summary of the Circular Economy, its validity challenge, and its future potential in their article, “Coming Full Circle: Why Social and Institutional Dimensions Matter for the Circular Economy.”[xix] They first point out that our modern inclination toward biomimicry and inspiration from natural systems can lead to short-sightedness in pursuing true global sustainability:
Analogy with natural systems allows practitioners and researchers in [Industrial Ecology] to disengage, for the most part, with questions related to people and power relations.
In other words, there is a kind of danger in using ecological analogy to describe innovation and design goals. In human-centered systems, personal philosophies, emotions, debate, and interpersonal conflict are factors in nudging along our production and material systems. The pursuit of ecologically-inspired system design, or biomimicking product design, can thus lead to major blind spots in the quest for better resource management. The authors urge CE practitioners to consider the full circle of factors, including tough subjects like wealth inequality and the “economic constraints of competitiveness.” They trace the history and current status of the Social and Solidarity Economy, a set of guiding principles for communities, governments and businesses that places emphasis on social rather than financial outcomes. These principles, they claim, could help to lower the cultural and political barriers that hamstring the CE’s potential. For example, if equipment sharing among small businesses or neighbors became normalized, the contaminated interaction calculus would change, enabling higher rates of sharing, durability and repair. In the authors’ words, “social and solidarity principles fill the gap toward CE opportunities that would otherwise be cost-ineffective.”
Slowing and Shrinking the Circle
In the introduction to this issue of the Journal of Industrial Ecology, the editors state:
The basic premises of the CE appear to be closing and slowing loops. Closing loops refers to (postconsumer waste) recycling, slowing is about retention of the product value through maintenance, repair and refurbishment, and remanufacturing, and narrowing loops is about efficiency improvements, a notion that already is commonplace in the linear economy.[xx]
Taking in the collected observations of the authors in Exploring the Circular Economy, it seems we should add shrinking loops to the list of CE premises. Many authors, in citing rebound effects and the historical failure of recycling initiatives to reduce aggregate global impacts, stress the need to shrink material throughput. Quoting once more from Zink and Geyer, “it is necessary that circular economy activities either have no effect on or decrease aggregate demand for goods.”
Additionally, most seem to agree that this shrinking cannot simply be left to products and technology, as social aspects play a large role in enabling solutions like reuse, refurbishment, and the “emotional durability” of materials. Neither can we rely on virtualization – the moving of information and services to the digital realm – to dematerialize the economy, as rebound effects are strong there too.
Our reading of this special issue of the Journal of Industrial Ecology, leads us to conclude that there are two major gaps in the Circular Economy’s relevance for achieving global sustainability. It has not developed language or methods, or necessarily acknowledgement, of the need to shrink and slow material throughput. These gaps are clearly shown by industrial ecology experts examining CE from many scales and angles. Figure 3 describes the transition to a circular economy by closing, slowing and shrinking loops, and conceptualizes a combined pathway forward.
There are many potential paths to slowing and shrinking, some defined in this issue, and many more needing research and refinement. If such refinement is not pursued, Circular Economy practitioners will be remembered as Alchemists, or as Blomsma and Brennan might say, they will experience “construct collapse.” The introduction to a 1911 re-print of Robert Boyle’s Sceptical Chymist reads:
When a man’s words mean anything, or everything, or nothing, and neither he nor any hearer of them knows exactly what they mean, they cover every possible contingency, and are full of solace to himself and to many others, because each hearer has his own particular way of allowing the words to reverberate in his brain and stir his emotions.
Hence, let this be a call to heed the advice of industrial ecologists to not ignore rebound effects, to consider aggregate global impacts, and to incorporate social dimensions into Circular Economy aims and initiatives. This moment in the publishing history of the Journal of Industrial Ecology is also an enabling one for the Circular Economy. Here is an honest inquiry into CE’s alchemical past and potentially rigorous future, aimed at understanding and better managing material flow in the service of global sustainability.
A shorter version of this article was previously published at the Worldwatch Institute blog: http://blogs.worldwatch.org/circular-economy-sustainable/”
John Mulrow is a PhD Candidate in Civil & Materials Engineering at the University of Illinois at Chicago, USA.
Victoria Santos is a PhD Candidate in Energy & Environmental Planning, at the Federal University of Rio de Janeiro, Brazil, and is a Visiting Researcher at Delft University of Technology, The Netherlands.
[i] Boyle, Robert. 1935. The Sceptical Chymist. London: J.M. Dent & Sons. (originally published 1661)
[ii] Bocken, Nancy M. P., Paavo Ritala, and Pontus Huotari. 2017. “The Circular Economy: Exploring the Introduction of the Concept Among S&P 500 Firms.” Journal of Industrial Ecology 21 (3): 487–90. doi:10.1111/jiec.12605.
[iii] Cullen, Jonathan M. 2017. “Circular Economy: Theoretical Benchmark or Perpetual Motion Machine?” Journal of Industrial Ecology 21 (3): 483–86. doi:10.1111/jiec.12599.
[iv] Linder, Marcus, Steven Sarasini, and Patricia van Loon. 2017. “A Metric for Quantifying Product-Level Circularity.” Journal of Industrial Ecology 21 (3): 545–58. doi:10.1111/jiec.12552.
[v] Hollander, Marcel C. den, Conny A. Bakker, and Erik Jan Hultink. 2017. “Product Design in a Circular Economy: Development of a Typology of Key Concepts and Terms.” Journal of Industrial Ecology 21 (3): 517–25. doi:10.1111/jiec.12610.
[vi] Stahel, W. R. 2010. The Performance Economy, 2nd ed. London: Palgrave Macmillan.
[vii] Blomsma, Fenna, and Geraldine Brennan. 2017. “The Emergence of Circular Economy: A New Framing Around Prolonging Resource Productivity.” Journal of Industrial Ecology 21 (3): 603–14. doi:10.1111/jiec.12603.
[viii] “Model T Facts | Ford Media Center.” 2017. Accessed August 16. https://media.ford.com/content/fordmedia/fna/us/en/news/2013/08/05/model-t-facts.html
[ix] “Table 4-23: Average Fuel Efficiency of U.S. Light Duty Vehicles | Bureau of Transportation Statistics.” 2017. Accessed August 16. https://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/html/table_04_23.html.
[x] Zink, Trevor, and Roland Geyer. 2017. “Circular Economy Rebound.” Journal of Industrial Ecology 21 (3): 593–602. doi:10.1111/jiec.12545.
[xi] Tisserant, Alexandre, Stefan Pauliuk, Stefano Merciai, Jannick Schmidt, Jacob Fry, Richard Wood, and Arnold Tukker. 2017. “Solid Waste and the Circular Economy: A Global Analysis of Waste Treatment and Waste Footprints.” Journal of Industrial Ecology 21 (3): 628–40. doi:10.1111/jiec.12562.
[xii] OECD (Organization for Economic Cooperation and Development). 2011. “Resource productivity in the G8 and the OECD—A report in the framework of the Kobe 3R Action Plan.” Accessed August 16. www.oecd.org/env/waste/47944428.pdf.
[xiii] Baxter, Weston, Marco Aurisicchio, and Peter Childs. 2017. “Contaminated Interaction: Another Barrier to Circular Material Flows.” Journal of Industrial Ecology 21 (3): 507–16. doi:10.1111/jiec.12612.
[xiv] Peiró, Laura, Fulvio Ardente, and Fabrice Mathieux. 2017. “Design for Disassembly Criteria in EU Product Policies for a More Circular Economy: A Method for Analyzing Battery Packs in PC-Tablets and Subnotebooks.” Journal of Industrial Ecology 21 (3): 731–41. doi:10.1111/jiec.12608.
[xv] Ness, David A., and Ke Xing. 2017. “Toward a Resource-Efficient Built Environment: A Literature Review and Conceptual Model: Towards a Resource Efficient Built Environment.” Journal of Industrial Ecology 21 (3): 572–92. doi:10.1111/jiec.12586.
[xvi] Lèbre, Éléonore, Glen Corder, and Artem Golev. 2017. “The Role of the Mining Industry in a Circular Economy: A Framework for Resource Management at the Mine Site Level: The Role of the Mining Industry in a Circular Economy.” Journal of Industrial Ecology 21 (3): 662–72. doi:10.1111/jiec.12596.
[xvii] McDowall, Will, Yong Geng, Beijia Huang, Eva Barteková, Raimund Bleischwitz, Serdar Türkeli, René Kemp, and Teresa Doménech. 2017. “Circular Economy Policies in China and Europe.” Journal of Industrial Ecology 21 (3): 651–61. doi:10.1111/jiec.12597.
[xviii] Mulrow, John S., Sybil Derrible, Weslynne S. Ashton, and Shauhrat S. Chopra. 2017. “Industrial Symbiosis at the Facility Scale.” Journal of Industrial Ecology 21 (3): 559–71. doi:10.1111/jiec.12592.
[xix] Moreau, Vincent, Marlyne Sahakian, Pascal van Griethuysen, and François Vuille. 2017. “Coming Full Circle: Why Social and Institutional Dimensions Matter for the Circular Economy: Why Social and Institutional Dimensions Matter.” Journal of Industrial Ecology 21 (3): 497–506. doi:10.1111/jiec.12598.
[xx] Bocken, Nancy M. P., Elsa A. Olivetti, Jonathan M. Cullen, José Potting, and Reid Lifset. 2017. “Taking the Circularity to the Next Level: A Special Issue on the Circular Economy.” Journal of Industrial Ecology 21 (3): 476–82. doi:10.1111/jiec.12606.