“Sustainable” is easy to define. It is the ability to continue indefinitely activities in any defined place such as an ecosystem or a geographic governmental unit. This means the activities cannot degrade a place, else the “indefinitely” cannot be used because activities supported will be diminished with the degradation. (This, of course, is where we are on the midcoast, with what can be supported continuously declining due to declining support features such as natural resources, even as demands on the same limited place increase and accelerate the decline with growing development and population.) In short, places like the midcoast are being screwed for the long term for the sake of some quickie short-term returns to a relative few.
One does not need to know about everything necessary for a kind of human activity to calculate sustainability. Rather, one can take the most critical local resource in short supply--or, better, two or three resources in short supply--determine how much is available in the leanest of times (a 100-year low, for example), and then determine how much of the scarce resource(s) can be extracted in those lean times without degrading the supportive system. Once one determines the amount that can be extracted, one can then easily calculate how much total combined activity of given kinds and degrees can be sustained.
It’s logical, quantitative, fairly simple, physical (rather than based on woo-woo abstractions), economic, efficient, and responsible. No wonder those few who line their pockets by wrecking places and communities at the expense of everyone else don’t like the concept of sustainability.
Carl May