Sustainability is the capacity to endure. In ecology the word describes how biological systems remain diverse and productive over time.
For humans it is the potential for long-term maintenance of well being, which in turn depends on the well being of the natural world and the responsible use of natural resources.
Sustainability has become a wide-ranging term that can be applied to almost every facet of life on Earth, from local to a global scale and over various time periods. Long-lived and healthy wetlands and forests are examples of sustainable biological systems. Invisible chemical cycles redistribute water, oxygen, nitrogen and carbon through the world's living and non-living systems, and have sustained life for millions of years. As the earth’s human population has increased, natural ecosystems have declined and changes in the balance of natural cycles has had a negative impact on both humans and other living systems.
There is abundant scientific evidence that humanity is living unsustainably, and returning human use of natural resources to within sustainable limits will require a major collective effort. Ways of living more sustainably can take many forms from reorganising living conditions (e.g., ecovillages, eco-municipalities and sustainable cities), reappraising economic sectors (permaculture, green building, sustainable agriculture), or work practices (sustainable architecture), using science to develop new technologies (green technologies, renewable energy), to adjustments in individual lifestyles that conserve natural resources.
The word sustainability is derived from the Latin sustinere (to hold). Dictionaries provide more than ten meanings for sustain, the main ones being to “maintain", "support", or "endure”. However, since the 1980s sustainability has been used more in the sense of human sustainability on planet Earth and this has resulted in the most widely quoted definition of sustainability and sustainable development, that of the Brundtland Commission of the United Nations on March 20, 1987: “ sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. ”
At the 2005 World Summit it was noted that this requires the reconciliation of environmental, social and economic demands - the "three pillars" of sustainability. This view has been expressed as an illustration using three overlapping ellipses indicating that the three pillars of sustainability are not mutually exclusive and can be mutually reinforcing.
The UN definition is not universally accepted and has undergone various interpretations.What sustainability is, what its goals should be, and how these goals are to be achieved is all open to interpretation. For many environmentalists the idea of sustainable development is an oxymoron as development seems to entail environmental degradation. Ecological economist Herman Daly has asked, " what use is a sawmill without a forest? " From this perspective, the economy is a subsystem of human society, which is itself a subsystem of the biosphere, and a gain in one sector is a loss from another. This can be illustrated as the three concentric circles.
A universally accepted definition of sustainability is elusive because it is expected to achieve many things. On the one hand it needs to be factual and scientific, a clear statement of a specific “destination”. The simple definition "sustainability is improving the quality of human life while living within the carrying capacity of supporting eco-systems", though vague, conveys the idea of sustainability having quantifiable limits. But sustainability is also a call to action, a task in progress or “journey” and therefore a political process, so some definitions set out common goals and values. The Earth Charter speaks of “ a sustainable global society founded on respect for nature, universal human rights, economic justice, and a culture of peace. ”
In the 21st century there is heightened awareness of the threat posed by the human-induced greenhouse effect. Ecological economics now seeks to bridge the gap between ecology and traditional neoclassical economics: and proposes an inclusive and ethical economic model for society. Many new techniques have arisen to help measure and implement sustainability, including Life Cycle Assessment, Cradle to Cradle, Ecological Footprint Analysis, and green building. The work of Bina Agarwal and Vandana Shiva amongst many others, has brought some of the cultural knowledge of traditional, sustainable agrarian societies into the academic discourse on sustainability, and blended that knowledge with modern scientific principles.