A paradigm shift in sustainability: from lines to circles

The concept of sustainability is attracting great attention as societies become increasingly aware of the environmental consequences of their actions. One of the most critical challenges that humankind is facing is the scarcity of resources, which are expected to reach their limits in the foreseeable future. Associated with this, there is increasing waste generated as a consequence of rapid growth in the world population (particularly inurban areas) and aparallel rise in global income. To cope with these problems, a linear strategy has been applied to increase efficiency by reducing the use of materials and energy in order to lessen environmental impacts. However, this cradle to grave approach has proven inadequate, due to a lack of attention to several economic and social aspects. A paradigm shift is thus required to re-think and innovate processes (as early as inthe design phase) in such a way that materials and energy are used more effectively within aclosed-loop system. This strategy, known as the cradle to cradle approach, relies on the assumption that everything is aresource for something else since no waste is ever generated in nature. In line with the cradle to cradle approach, the bio-inspired circular economy concept aims at eco-effectiveness, rather than eco-efficiency. While the circular economy has neither a confirmed definition nor a standardized methodology, it nonetheless carries significant importance, since it “is restorative and regenerative by design and aims to keep products, components, and materials at their highest utility and value at all times, distinguishing between technical and biological cycles,” in accordance with the goals of the 2030 Agenda for Sustainable Development. Despite some controversial opinions that “circles are not spirals, and for growth to occur, spirals with ever-increasing radii are required,” the circular economy concept is taking a central role in the sustainable development debate and, for this reason, deserves attention. The aim of this paper is to shed light on this debate, pointing out the main features of the emerging circular paradigm along with sustainability transition theories and circularity evaluation tools