Human settlements and sustainability: a crucial and open issue

The human habitation of the surface of the planet has led, especially since the mid-twentieth century, to an enormous increase in the built up area. This phenomenon concerns both the oldest industrialised countries, such as European Union and the United States, and the so-called emerging countries in Asia, Africa and Latin America. The urbanised built area has increased in different ways, but has led everywhere to the destruction of large portions of virgin soil, the loss of biodiversity in the number and type of species in fauna and flora, and often the total or partial impairment of ecosystem functions of enormous environmental value (such as the evapotransportive mechanisms of soil and vegetation). Although the curve of global population growth is slowing, the growth of urban areas continues to expand, even in countries which have long been industrialised, where the spread of building has given rise to cities dispersed over a territory so that there is no longer a recognisable clear division between the city and the countryside. In fact, contemporary cities are the main consumers of all environmental resources, from water to food, including energy and environmental stressors, and are responsible for 80% of CO2 emissions into the atmosphere. The ecosystem surface required to sustain a large city on the planet today can be about 200 times larger than its physical size. The urban civilisation of the 21st century, which at a superficial glance may appear as a symbol of the human capacity to radically adapt and transform the natural habitat to its own needs, is also a witness to the unsustainability of the human footprint on earth. Radically rethinking cities and human settlements entails an equally radical rethinking of our economic and development model, but it is a necessary and strategic task if we really want to face the challenge of sustainability with appropriate instruments.