a measure of human demand on the earth's ecosystems
Ecological footprint The ecological footprint measures human demand on nature, i.e., the quantity of nature it takes to support people or an economy. It tracks this demand through an ecological accounting system. The accounts contrast the biologically productive area people use for their consumption to the biologically productive area available within a region or the world (biocapacity). In short, it is a measure of human impact on Earth's ecosystem and reveals the dependence of the human economy on natural capital.
History of sustainability Ecology had now gained general acceptance as a scientific discipline, and many concepts vital to sustainability were being explored. These included: the interconnectedness of all living systems in a single living planetary system, the biosphere; the importance of natural cycles (of water, nutrients and other chemicals, materials, waste); and the passage of energy through trophic levels of living systems.[31]