Our earth is a closed ecological system, with sunlight providing the only inflow of energy. Therefore, society will have to create its living environment from earth-available resources and energy stemming directly or indirectly (e.g. wind, tides, biomass) from sunlight.
Until late in the 20th century the common perception was that the food and energy potential of our globe would be able to sustain the growing population for many years to come, and that human activities had only a minor influence on the climate. Recently, however, it has become clear that the human influence on its own habitat and all living organisms on Earth is much larger than previously anticipated.
If we continue in this way, we will slowly but surely destroy our own living environment, depleting all our resources and initiating the extinction of many species. Evidence for this is abundantly available, such as the disturbingly increasing soil and water poisoning, an ascending average global temperature, the depletion of fossil fuels (currently without good alternatives), and problematic food supplies in a growing number of countries.
In fact, with the speed at which most of our resources are being consumed, the amounts of available fuels, minerals, metals and even drinking water available to human society are in danger of becoming limited already on the time-scale of decades, not centuries.
To ensure ourselves and our children a viable future a radical transformation is inevitable - a transformation of a society based on the exploitation of earthly resources, to a sustainable society that is more in balance with the environment. This requires a paradigm shift in technology and new knowledge. Next to solving the energy issue, the sustainable transformation of (recyclable) raw materials into products - using mild and clean conditions - is crucial for a sustainable society.