The most important of the three pillars of sustainability is environmental sustainability. If this is not solved, then no matter how hard we try the other pillars cannot be made strong because they are dependent on the greater system they live within, the environment.
Environmental sustainability is the rates of renewable resource harvest, pollution creation, and non-renewable resource depletion that can be continued indefinitely. If they cannot be continued indefinitely then they are not sustainable.
Definition of environmental sustainability has been implemented by Herman Daly, one of the early pioneers of ecological sustainability. In 1990 he proposed that:
- For renewable resources, the rate of harvest should not exceed the rate of regeneration (sustainable yield);
- [For pollution] The rates of waste generation from projects should not exceed the assimilative capacity of the environment (sustainable waste disposal); and
- For non-renewable resources, the depletion of the non-renewable resources should require the comparable development of renewable substitutes for that resource.