What is a green city?

Before proceeding to answer this question, a few terms must be defined. First, even if the specific challenges that the city centers are facing are often highlighted in articles, the term “city” generally refers to a broader metropolitan area. For example, “Milan” represents the large metropolitan area surrounding the city, not just the city lying within the city limits. The same applies to other major cities in different parts of the world, such as Chicago, London, Tokyo, São Paulo, etc.

A metropolitan area is made up of a central area containing a substantial population nucleus, together with adjacent communities having a high degree of economic and social integration with that nucleus. Metropolitan areas may therefore include several cities/urban agglomerations. Focusing on metropolitan areas makes sense because the majority of people and jobs are concentrated in metropolitan areas (over 50% worldwide and 70% in Europe), but outside of the proper “center”.

Defining a “green” metropolis is a more difficult task. Most of us have an intuitive sense of what defines a green city, like Portland, Oregon, as compared to urban centers defined as “gray”, like Mexico City.

Apart from having cleaner air, green cities also encourage “green behaviors”, like the use of public transport, with their environmental impact being relatively low so as, in some cases, to almost arrive at zero impact. Can this definition of a green city be translated into objective indicators of urban environmental quality?

In this sense, there are different types of evaluations. Environmentalists stress the importance of monitoring the size of a city’s ecological footprint. This approach focuses on what people consume and how much carbon dioxide is produced as a byproduct of urban consumption and manufacturing…