Unsustainable development compromises the ability of future generations to meet their needs. Phenomena including global warming, destruction of the ozone shield, acidification of land and water, desertification and soil loss, deforestation and forest decline, diminishing productivity of land and waters, and extinction of species and populations, demonstrate that human demand is exceeding environmental support capacities. Population growth increases poverty and deprived people are forced to undermine the productivity of the land on which they live. It is extremely difficult for people, or other species, to adjust to change at this rate.
Sustainable development requires economic efficiency and equity within and between generations. Economic efficiency is the production of the optimal combination of outputs by means of the most efficient combination of inputs. Equity is the expansion of opportunities for the disadvantaged and passing on to future generations a portfolio of assets of equal or greater value than the existing one. If one group increases its welfare at the expense of another, it should compensate the other by transfer of assets of equal or greater value, both within generations and between generations. Such compensations would be made now rather than in the future, because the welfare of the deprived group has actually been reduced, and equity is not served by compensation that is merely hypothetical.
In order to ensure that the total value of the portfolio of assets is not diminished: the assets must be valued to reflect all their current and future contributions to future welfare; incentives must be provided so that individuals and organizations manage the assets according to these values; depletion or degradation of one asset must be compensated by an increase in the value of another.
The industrial way of life with its ethos of expansion is not sustainable. Its termination within the lifetime of someone born today is inevitable – unless it continues to be sustained by an entrenched minority at the cost of imposing great suffering on the rest of humanity. We can be certain, however, that sooner or later it will end (only the precise time and circumstances are in doubt).
Natural systems function with numerous built-in limits which, if transcended, result in resource exhaustion, environmental impact, and degradation of person and planet. Such outcomes are clearly not sustainable.