In the field of sustainable cities, Herbert Girardet's name is legendary. He has made the discipline his life's work. Besides being the author of 11 books on the subject he is also co-founder of the World Future Council.

But now he's left the concept of sustainability behind, moving on to define a new, more dramatic concept: the idea of regenerative cities. And that is the theme of his new book Creating Regenerative Cities. 

The first half of the book sets out the problem, the idea of Petropolis. In this first part of a two-part interview he talks about the concept of regenerative cities, the existing state of affairs defined by Petropolis, and urban metabolism.

To create regenerative cities is a new challenge for policymakers. 

Regenerative cities are cities which we pay back the debt we take from nature. It takes is model from nature where there is no waste and everything gets reused without an increase in entropy. Entropy is disorder, defined in this case by resources emerging from their consumption within cities in a less useful, downcycled state which at the worst cause terrible pollution.

Just as a house can be seen as a nexus through which various processes occur, so can a city. In the case of a house inputs are water, electricity, heating, cooling, food and products. The outputs are wastewater, solid wastes, heat.

In the case of the city the inputs are similar but the outputs more varied and include the products of agriculture such as phosphate and nitrate pollution with the consequent destruction of aquatic and marine ecosystems. Air-pollution is another serious output in the form of hydrocarbon particles. Climate change is a global problem.

Since cities are increasingly responsible for the majority of environmental damage caused by human beings, then Herbert Girardet argues that it is absolutely necessary for them to adopt new policies that foster the closed loop approach, where either there are no negative outputs, or they become the inputs for processes which generate positive outputs.

You can watch the second part here. It looks at how to create a regenerative city, with case studies such as Adelaide, Bristol and Copenhagen, and whether Herbert, with his vast experience, is optimistic for the future.