4. Ecological soil quality for sustainable cities

The demographic revolution of the last century has seen the world's population rise from 3 billion in 1960 to 7.5 billion today. This trend is set to continue, with forecasts predicting a population of 9 billion by 2050! At the same time, man has become a predominantly urban species, with urbanized environments concentrating more than half the world's population. This rapid evolution has been accompanied by a number of negative externalities (i.e. increased waste, production of relegated spaces, pollution, artificialization, urban sprawl on arable land, development of heat islands, reduced biodiversity, hazards and vulnerability of territories to climate change). For example, the major metropolises of Northern Europe appropriate for their resource consumption and waste storage a forest or agricultural area at least 565 to 1,130 times larger than the surface area of the cities themselves....