ABSTRACT
Some other contemporary human systems, aside from energy, are also not sustainable. These include many aspects of use of natural resources (soil, water, biota), as well as the economic-cultural system employed to keep raising output and consumption-the activities generally used to defi ne economic growth. This system was seen as so essential that Alan Greenspan felt it necessary to lower interest rates nearly to zero in order to sustain the consumption bubble of the 1990s and the early twenty-fi rst century. Consumers were encouraged to borrow money on the basis of infl ated house values, so as to be able to spend beyond their incomes.
