Sustainability is a characteristic of a process or state that can be maintained at a certain level indefinitely.

Sustainability focuses on providing the best outcomes for both the human and natural environments now, and into the indefinite future.

In recent years an academic and public discourse has led to the use of the word sustainability in reference to how long human ecological systems can be expected to be usefully productive.

The implied preference would be for systems to be productive indefinitely, or be 'sustainable." For instance, "sustainable agriculture" would require agricultural systems expected to last indefinitely, "sustainable development" would be development of economic systems that last indefinitely, and so on.

A side discourse relates the term sustainability to longevity of natural ecosystems and reserves, but the greatest emphasis has been on human systems and anthropogenic problems, such as anthropogenic climate change, or the obviously anthropogenic depletion of fossil fuel reserves.

It is perhaps meaningful, and pragmatic, to speak of practices being "more sustainable" or "less sustainable." Thus energy saving compact florescent light bulbs can be considered more sustainable than incandescent ones, and so forth.

Definitions of sustainability abound, and the popularity of the term has led to competing definitions, and much confusion.

One of the most oft-cited definitions of sustainability is the one created by the Brundtland Commission, led by the former Norwegian Prime Minister Gro Harlem Brundtland. The Commission defined sustainable development as development that "meets the needs of the present without compromising the ability of future generations to meet their own needs." Sustainability relates to the continuity of economic, social, institutional and environmental aspects of human society, as well as the non-human environment.

Definitions, metrics and indices

Sustainability can be defined both qualitatively in words, as an ethical/ecological proposition such as the Bruntland definition above, and quantitatively in terms of system life expectancy and the trajectory of certain factors or terms in the system.

Quantitative analysis in sustainability thinking typically uses system dynamics modeling as systems are often non-linear and so-called feedback loops are key factors. So, for instance, important human ecological sub-systems that could be analyzed or modeled in this way might include the nitrogen cycle in sustainable agriculture, or the depletion of oil reserves.

In order to distinguish quantitatively and qualitatively which human economic activities are destructive and which are benign or beneficial, various definitions/models of sustainability have been developed.

Environmental Sustainability Index

In 2004, a joint initiative of the Yale Centre for Environmental Law and Policy (YCELP) and the Centre for International Earth Science Information Network (CIESIN) of Columbia University, in collaboration with the World Economic Forum and the Directorate-General Joint Research Centre (European Commission) also attempted to construct an Environmental Sustainability Index (ESI).

This was formally released in Davos, Switzerland, at the annual meeting of the World Economic Forum (WEF) on 28 January 2005. The report on this index made a comparison of the WEF ESI to other sustainability indicators such as the Ecological footprint Index.

However there was no mention of the energy sustainability index.

Nevertheless writers like Leone (2005) and Yi et al. have also recently suggested that the energy sustainability index has significant utility.

Common principles

Some people now consider the term "sustainable development" as too closely linked with continued material development, and prefer to use terms like "sustainability", "sustainable prosperity" and "sustainable genuine progress" as the umbrella terms. Despite differences, a number of common principles are embedded in most charters or action programmes to achieve sustainable development, sustainability or sustainable prosperity.

These include:

• Dealing transparently and systemically with risk, uncertainty and irreversibility.

• Ensuring appropriate valuation, appreciation and restoration of nature.

• Integration of environmental, social, human and economic goals in policies and activities.

• Equal opportunity and community participation/Sustainable community.

• Conservation of biodiversity and ecological integrity.

• Ensuring inter-generational equity.

• Recognizing the global integration of localities.

• A commitment to best practice.

• No net loss of human capital or natural capital.

• The principle of continuous improvement.

• The need for good governance.

Sustainability and business

The World Business Council for Sustainable Development, founded in 1995, has formulated the business case for sustainable development and argues that "sustainable development is good for business and business is good for sustainable development". This view is also maintained by proponents of the concept of industrial ecology. The theory of industrial ecology declares that industry should be viewed as a series of interlocking man-made ecosystems interfacing with the natural global ecosystem.

According to some economists, it is possible for the concepts of sustainable development and competitiveness to merge if enacted wisely, so that there is not an inevitable trade-off^[12]. This merger is being motivated by the following six facts (Hargroves & Smith 2005):

1. Throughout the economy there are widespread untapped potential resource productivity improvements to be made to be coupled with effective design.

2. There has been a significant shift in understanding over the last three decades of what creates lasting competitiveness of a firm.

3. There is now a critical mass of enabling technologies in eco-innovations that make integrated approaches to sustainable development economically viable.

4. Since many of the costs of what economists call ‘environmental externalities’ are passed on to governments, in the long-term sustainable development strategies can provide multiple benefits to the tax payer.

5. There is a growing understanding of the multiple benefits of valuing social and natural capital, for both moral and economic reasons, and including them in measures of national well-being.

6. There is mounting evidence to show that a transition to a sustainable economy, if done wisely, may not harm economic growth significantly, in fact it could even help it. Recent research by ex-Wuppertal Institute member Joachim Spangenberg, working with neo-classical economists, shows that the transition, if focused on improving resource productivity, will lead to higher economic growth than business as usual, while at the same time reducing pressures on the environment and enhancing employment.

It is an unresolved question as to whether all of the attempts at definitions have anything to do with the compound constructs of sustainability investment advanced by network economics and systemic entrepreneurs.

Barriers to ecological sustainability

Despite the now overwhelming evidence that the human species is set on a population adjustment course of immense proportions, and despite long-standing and widespread public awareness of the seriousness of the consequence (e.g., Nelson, 1986; Yankelovitch, et al., 1983; Diamond, Jared (2005) ), it seems impossible to alter the course of our destiny.

This is generally attributed to “change resistance”, viewed as involving change in individual values, whether at personal, corporate, or collective levels. Unfortunately, it has been frequently demonstrated,  that people’s values are, in general, in the right place. The problem is to enact them. This has led to the preparation of numerous “wish lists”—such as that compiled by Shah, H., & Marks, N. (2004)—drawing together many recommendations for government action.

Government and individual failure to act on the available information is widely attributed to personal greed (deemed to be inherent in human nature) especially on the part of international capitalists. But even Karl Marx did not suggest this, instead highlighting sociological processes which have been in operation for thousands of years.

If fault is to be found with Marx's work it can be argued that it lies elsewhere. Because he believed that the collapse of capitalism was imminent, he never discussed how to run society in an innovative way in the long term public interest.