Circular Cities, the way to urban sustainability

Circular Cities, the way to urban sustainability

Speech by Prof. Fabrizio Zucca, coordinator of the Eurispes Laboratory on Sustainability

Meeting “The future of western metropolis: what’s next?”

Milan, 20 October 2022 – Catholic University of the Sacred Heart

Promoted by Centro Ateneo per la Dottrina sociale della Chiesa, Fondazione Sinderesi and Konrad-Adenauer-Stiftung


In 1900 the world’s population did not exceed 1.7 billion people, of which only 0.7 were urbanised and lived in cities. Demographic projections indicate that by 2050 there will be 10 billion of us, a year that could also represent the world’s demographic ‘peak’ before a period of adjustment and decline. Of the 10 billion people, it is estimated that between 7.5 and 8 billion will live in urban areas. This is an increase that cannot only be read through these few numbers but also in terms of how cities have changed over the years. Until the 1950s, the average size of the city still closely linked it to the immediate area and region that provided most of the resources needed for sustenance.

Even today, if one looks mainly at Asia but also at other continents to a lesser extent, cities have reached population sizes that were inconceivable even only sixty or seventy years ago. If we think about the municipality – which is the equivalent of our metropolitan areas – of Shanghai, we are talking about an urban agglomeration of just over 30 million inhabitants with a density of 4.8 million inhabitants per km2. In comparison, Lombardy does not reach 10 million, with a density of just over 400,000 inhabitants per km2.

The growth in size has also radically altered the nature of cities: it is therefore not just a question of an increase in scale, but precisely of the development of urban areas that, while they maintain their name in comparison to the past, are hard to compare, except for the governance system that has often remained stuck in the past and is not very effective anymore. Just think about Milan. If we fly over Lombardy at night, we realise that it has an urban development that goes from Novara to Brescia, from west to east, and from Lodi or Pavia to Como, Varese and Lecco from south to north. The government of this large urban area that insists on Milan has a power that is split into multiple administrations that are entrusted with all the management tasks over their territories.

Along with size, the relationship between city and region and the dynamics within cities has also changed dramatically. The cycle of production-consumption-waste-generation and disposal has broken down, cities have become great resources absorbers through the consumption of products and energy that are no longer found within the city or the surrounding region, but can be distributed anywhere in the world; the same applies to waste management, which is no longer used to regenerate the territory, but must be disposed of, taken by the cities to other territories to preserve the soil that can potentially be used for the growth of the urban agglomerations themselves and sometimes even abroad.

From this perspective, the real problem to date has been related to supply and disposal, processes for which ad hoc infrastructures have been created over time that require high resources and energy consumption.

Resources are one of the keys to the change towards a circular model of cities, which are responsible for most of their consumption and more than 75% of the energy produced worldwide. Beyond the debate on energy, fossil or renewable, which has characterised recent months also due to the skyrocketing price of gas, it must be clear that the problem of shortage covers all non-renewable resources (in figure 1, the Mendeleev table shows a clear projection of the state of resources in 100 years’ time) is the cause of the continuous shift of overshoot day (indicates, illustratively, the day on which mankind consumes all the resources produced by the planet in the entire year) which, year by year, is brought forward – some 20 years ago it was still in December, while in 2022 it was as late as 28 July.

The linear model of the city, seen as a significant resource absorber, is becoming less and less sustainable. The large influx of resources needed for supply and consumption that often results in waste – and the consequent creation of waste that requires disposal – creates more and more environmental and social issues that require action. It is, therefore, necessary not only with a view to reduction and future sustainability but also to regenerate the urban ecosystem.

The term ecosystem introduces three key concepts. The first is that of change, in the sense of the vital activity of cities that are constantly changing; the second is of socio-economic nature and implies the interaction between those who live in the city and the city itself with its infrastructures; the third is of balance, intended as the city’s capacity to be sustainable over time and to regenerate itself. In these concepts lies a paradigm capable of rethinking the production-consumption-disposal process, making it capable of reducing the consumption of resources used and consequently also of the energy needed to sustain the flow.


A circular city is an urban system in which resources flow in a circular path, the ecosystem regenerates, and the technological and social systems (infrastructure and community) evolve as context conditions change. A circular development can implement circular systems, activities and infrastructures through spatial planning and economic development processes, giving a central role to development goals (SDGs) such as inter-generational equity, the future and environmental protection.

The circular city can offer its citizens what they need when they need it and, above all, at prices that are accessible to the broadest range of people in order to guarantee the highest rate of inclusion through processes of efficiency, reuse, repair and regeneration of objects of use using renewable energy sources.


The picture below shows the circular mechanism that brings production processes into the city – through the closing of the inner circles of both the biological and technical material cycles – that do not require new resources but instead make use of the material resources that are already present. Thus, production processes increase their life cycle and reduce waste, the use of transport infrastructures, land consumption and energy consumption.

In the socio-economic sphere, those processes develop new types of work based on often forgotten skills that allow them to continue to create development in the process of decoupling from the consumption of non-renewable resources through the creation of value provided by the work’s creativeness. The creation of local activities that allow for the reuse, repair and regeneration of objects also passes through the ability to design the objects themselves in a way that allows for modularity and ease of assembly and reassembly.

Over the years, many urban regeneration projects have been driven mainly by aesthetic, environmental and digital principles. They have produced marked processes of gentrification, as property prices have risen significantly, not allowing access to large sections of the population and excluding urban production projects based on product regeneration or urban agriculture.

Cities have started to include circularity indicators in their urban development plans only in more recent years. These indicators could foster the creation and maintenance of resource regeneration activities on the territory and the creation of new types of markets suitable for retaining resources and creating jobs for broader segments of the population without compromising the growth of housing prices. Cities such as Paris, London, Stockholm and Amsterdam have included references and actions for circular development in their growth plans; other cities have joined the OECD project on the circular city that provides guidelines and indicators for measuring and identifying the levers needed to foster change that is unlikely to be carried out by a top-down government process or by a single stakeholder. The possibility of success and intervention passes through awareness-raising, environmental education and collaboration among the city’s stakeholders both in the horizontal dimension (e.g. among citizens) and in the vertical dimension with public/private collaboration projects and by orienting the purchasing processes of public administrations towards locally produced goods, powered by urban mining and ecodesign processes.

Social Network