Sustainability, in general terms, is the ability to maintain balance of a certain process or state in any system. It is now most frequently used in connection with biological and human systems.

Sustainability has become a complex term that can be applied to almost every system on Earth, and is expressed in human organization concepts, such as; eco-municipalities, sustainable cities, and human activities and disciplines, such as; sustainable agriculture, sustainable architecture and renewable energy. For humans to live sustainably, the Earth's resources must be used at a rate at which they can be replenished. However, there is now clear scientific evidence that humanity is living unsustainably, and that an unprecedented collective effort is needed to return human use of natural resources to within sustainable limits.

Since the 1980s, the idea of sustainable human well-being has become increasingly associated with the integration of economic, social and environmental spheres.

Definitions of sustainability may be expressed as statements of fact, intent, or value with sustainability treated as either a "journey" or "destination." Where we are now, where we need to be going, and how we are to get there are all open to interpretation and will depend on the particular context under consideration. This difficult mix has been described as a dialogue of values that defies consensual definition. Sustainability has been regarded as both an important but unfocused concept like "liberty" or "justice" and as a feel-good buzzword with little meaning or substance.

The idea of sustainable development is sometimes viewed as an oxymoron because development inevitably depletes and degrades the environment. Consequently some definitions either avoid the word development and use the term sustainability exclusively, or emphasise the environmental component, as in "environmentally sustainable development."

The dimensions of sustainability are often taken to be: environmental, social and economic, known as the "three pillars".

Scheme of interaction of the three "pillars" of sustainable development. (Source: Wikipedia.)

These can be depicted as three overlapping circles (or ellipses), to show that they are not mutually exclusive and can be mutually reinforcing. While this model initially improved the standing of environmental concerns, it has since been criticised for not adequately showing that societies and economies are fundamentally reliant on the natural world. According to English environmentalist and author Jonathon Porritt, "The economy is, in the first instance, a subsystem of human society ... which is itself, in the second instance, a subsystem of the totality of life on Earth (the biosphere). And no subsystem can expand beyond the capacity of the total system of which it is a part."

Another representation showing economy and society bounded by the environment. (Source: Wikipedia.)

For this reason a second diagram shows economy as a component of society, both bounded by, and dependent upon, the environment. As the American World Bank ecological economist Herman Daly famously asked, "what use is a sawmill without a forest?" The concept of living within environmental constraints underpins the IUCN, UNEP and WWF definition of sustainability: "improving the quality of human life while living within the carrying capacity of supporting eco-systems."

The Earth Charter goes beyond defining what sustainability is, and seeks to establish the values and direction needed to achieve it: "We must join together to bring forth a sustainable global society founded on respect for nature, universal human rights, economic justice, and a culture of peace. Towards this end, it is imperative that we, the peoples of Earth, declare our responsibility to one another, to the greater community of life, and to future generations."

See Wikipedia "Sustainability" for continued discussion of the evolution of thinking about sustainability in human history...

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An economy is the realized social system of production, exchange, distribution, and consumption of goods and services of a country or other area. A given economy is the end result of a process that involves its technological evolution, civilization's history and social organization, as well as its geography, natural resource endowment, and ecology, among other factors. These factors give context, content, and set the conditions and parameters in which an economy functions.

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Community-based economics or just community economics encourages local substitution and a rejection of outside energy subsidy and coercion. It is most familiar from the lifeways of those practicing voluntary simplicity, including traditional Mennonite, Amish, and modern eco-village communities. However, it is also increasingly a priority in urban economics, where moral purchasing and local purchasing are increasingly cogent concerns.

It also includes various specific programs for community economics and local currency. Recently, the more mainstream approach of Independent Business Alliance organizing has spread across the U.S., helping independent, locally-owned businesses compete effectively and countering the spread of corporate chains at the local level. [The "Buy Local" movement is another aspect of community-based economics.]

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Economics – Proponents of industrial agriculture claim that large-scale factory farming is the most efficient way to produce huge quantities of inexpensive food and that without industrial agriculture, food prices would be excessively high. But the price of industrial food does not take into account the true costs of production. When these hidden environmental and health costs are factored in, industrial food costs more than sustainable.

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What is a local food system? – It takes more than some fertile land and interested shoppers to make local food a success. Farmers need education and training about how to grow the high quality food that local consumers look for. They also need local businesses and networks to buy, sell and trade supplies. Once crops are grown and harvested, they need to be shipped to market. Some farmers do their own shipping, while others depend on trucking companies. If local items are bound for the grocery store, they may make a stop at a local distribution center first. All the people and steps it takes to get food to market make up a local food system.

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