The Sustainability Challenge
Sustainability in its literal sense means the ability to sustain something over time. Our current economic activities are unsustainable as the depletion of our natural resources and the accumulation of wastes in our biosphere-geosphere are both occurring faster than the earth's ability to cope. The Malthusian view is that we will eventually reach a point where the earth's natural systems, including human life, can no longer survive.
In 1987 the World Commission on Environment and Development (better known as the Brundtland Commission) proposed a brief, widely quoted description of the major components in sustainable development:
"Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs."
The Stern report which is summarised in newsletter 64 confirms the urgency, not just from a "green" viewpoint but from that of a very rational economist, of getting on with the planetary engineering role we have so long neglected and concentrating on maintaining earth the way it should be.
"Dire predictions notwithstanding, we can still act to ensure a livable world. It is crucial that we know this: we can meet our needs without destroying our life-support system. We have the technical knowledge and the means of communication to do that. We have the savvy and the resources to grow sufficient food, ensure clean air and water, and generate the energy we require through solar power, wind and biomass. If we have the will, we have the means to control human population, to dismantle weapons and deflect wars, and give everyone a voice in democratic self-governance" 
Nature has had billions of years to evolve systems that work and a homeostasis amongst these systems. To live on the same planet we must act in harmony with the rest of the planet. Rather than dominating, nurturing, rather than just taking, giving, producing as well as consuming. Natural, like other forms of capital has limits. The need for innovative change has never been greater.
We can do something about all the problems on the planet by improving sustainability as they are all connected
Charles Darwin is reputed to have said "It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change." We must change our ways to survive.
 Macy, Joanna,"Coming Back To Life: Practices to Reconnect Our Lives, Our World" (pp. 16-17), New Society Publishers.