have to be addressed, such as: will land be set aside for natural ecosystems and wild animals?
On an individual level, if, for example, it is necessary to limit energy consumption, people may have to make choices about how they live and what they do. Perhaps deciding between using an electric car for personal transport for a year and flying half-way around the world for an annual holiday in a plane powered by biofuels.
Because of the need to allocate resources, it is not possible to state categorically that a specific part of a system is sustainable. For example, it is meaningless to say that a building is sustainable as this will depend on the interactions it has with other parts of society, such as land use, transport, utilities and other amenities. Indeed, the greatest efficiencies in resource utilisation may well come from an integrated design of a village or city. Even then, sustainability will probably depend on what happens in the rest of the country and ultimately the world.
Adaptability and resilience
While a system should avoid changing the environment to remain in equilibrium with it, some changes may be beyond the control of the system. For example, global warming has a momentum behind it that will take decades to slow down. On longer time scales, our current climate is probably an interglacial period between ice ages. During transitions from one set of stable environmental conditions to another, both the society and ecosystems must have the capability to adapt until a new equilibrium can be achieved.
Transient shocks also have the potential to disturb the equilibrium between a system and its environment. Examples include storms, earth quakes and tsunamis. To be resilient both society and ecosystems need to either absorb the shocks or quickly recover from them. Some ecosystems provide protection to both society and other ecosystems, for example coral reefs and mangroves protect coasts from storms. Such non-productive benefits are known as ecosystem services.
We have degraded some ecosystems by polluting them with wastes, others by over-exploitation, others still by destructive actions. This has reduced their productive capacity, their adaptability, their resilience and the quality of their services. Hence, we have already reduced the probability of sustainability for future generations. Therefore, as society moves towards equilibrium with the environment, we should also seek to restore we have caused to become degraded.
A sustainable society is one that is in equilibrium with its environment having closed the loops between its inputs and outputs. It differentiates between renewable and non-renewable resources, ensuring that ecosystems can supply or recycle the former while recycling the latter itself. It avoids making changes to the environment but where changes are outside its control, it ensures that both the systems within society and the ecosystems within the environment can adapt to those changes until a new equilibrium is attained. Likewise, it ensures that both are resilient to transient shocks.
Our society may have a long way to go and sustainability may not be certain, but restoring the productivity, adaptability and resilience of the ecosystems it has degraded will only help. The harnessing of renewable resources and using them more efficiently are areas of where improvement is vital. Finding new ways to recycle non-renewable resources or replacing them with renewable substitutes are opportunities for innovation. Clearly greater cooperation in managing ecosystems and allocating resources is going to become increasingly important. Not everything needs to be done immediately but some actions are more urgent than others and they need to be identified and priorities set.
By looking at their inputs and outputs, it can be simple to determine which parts of a system are not sustainable, but it is often meaningless to say that one part is sustainable without considering the whole. Therefore, it may be impossible to achieve sustainable development but development towards sustainability can be and should be o