75% of CO2 emissions are produced in cities. The world is facing major environmental challenges and cities are a major contributer to the consumption of energy, natural resources and emissions. So most discussions are about the ecological footprint of a city – a factor that describes the amount of land required to sustain its metabolism. Based on this definition Herbert Girardet, consultant to Habitat II, the UN agency concerned with sustainability in cities, calculated that London’s footprint, for example, is 125 times its surface area. This is the equivalent to Britain’s entire productive land. Another example is Tokyo. The raw materials on which the city feeds and processes the waste products it excretes takes 1.2 times the land area of the whole of Japan. If mountains and other regions are discarded and only habitable land included, then this becomes 3.6 times the land area of Japan.
No wonder that the center of attention within sustainable development is on reducing CO2 emissions with concepts like decentralized infrastructures for energy production, waste and water management systems evolving from today’s recycling model to a new model that includes the product lifecycle and inverse logistic procedures.