Getting serious about sustainability.

Sustainability and sustainable development are catchwords that dominate today's environmental science and policy discourse. It is easy to demonstrate that most of the activities of today's industrial society are unsustainable. Unfortunately, much of the talk about sustainability lacks a basic understanding of what truly sustainable activity would be. To set sustainability as a target or goal for our industrial society, we must be able to quantify that target or goal. We propose four basic steps to begin this process for one aspect of sustainability, the rate of use of resources: (i) establish the available supply of the chosen resource; (ii) allocate the annual permissible supply according to a reasonable formula or market process; (iii) establish the "recaptureable" resource base; and (iv) derive the sustainable limiting rate of use and compare to the current rate of use. We apply these sustainability measurement methods to three common materials in industrial society: zinc, germanium, and greenhouse gases. These examples demonstrate that with some basic (although potentially controversial) assumptions, quantitative sustainable use goals can be set and current performance relative to those goals can be evaluated. The assumptions and approximates we have used are meant to stimulate thought and debate, beginning a long conversation on the measurement of sustainability.