The biological and physical environment provides the economy with:

1. Resources such as water, air, fuels, food, metals, minerals, drugs and so on.
2. Services as for example the cycles of H₂O, C, CO₂, N, O₂; photosynthesis; soil formation.
3. Mechanisms to absorb waste.

According to an attempt to monetize all three global services (Costanza et al., 1997), their total value in 1997 was $33 trillion/year. This number gives us an idea of the importance of the environment.

Economic growth is based on these three services and since the global ecosystem does not grow, economic growth cannot continue indefinitely. It is claimed by several economists that substituting one form of capital for another solves the problem of finiteness of the ecosystem. But substitution has its limits too and often is impossible owing to the scale of the global ecosystem or the laws of nature. There is no substitute for a stable climate and there are no substitutes for extinct species and their services to nature.

In the last decades, we have witnessed dramatic environmental changes as a result of human economic activity. Global warming, stratospheric ozone depletion, species extinction, and exhaustion of natural resources provide strong evidence that development is currently unsustainable. As a result, there has been growing interest among policy-makers and scientists in the concepts of sustainability and sustainable development.

Sustainable development does not necessarily mean growth, but improvement of the various societal sectors, as for example health, education, or the state of the environment. So what is sustainable development?

In more general terms, sustainable development according to the Brundtland:

Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

or according to IUCN:

Development that improves the quality of human life within the carrying capacity of supporting ecosystems.

In general, sustainability integrates various aspects: environmental, economic, societal. It also covers different geographical scales: ecosystems, regions, countries, and the globe. Also it has a restricted time horizon: although sustainability encompasses long-term goals, it cannot be planned for thousands of years into the future; all the time we make adaptive decisions which bring us as close to our goals as possible.

References

• Costanza R, d'Agre R, de Groot R, Farber S, Grasso M, Hannon B, Limburg K, Ñame S, O'Neil RV, Raruelo J, Raskin RJ, Sutton P, van den Belt M (1997) The value of the world's ecosystem services and natural capital, Nature 387, 253–260.
• WCED (World Commission on Environment and Development) (1987) Our Common Future, Oxford University Press, Oxford.