How is sustainability determined for a product or system, and by whom?

Question

I see many questions on this site about the sustainability of various products or practices. I also see that some things which are considered sustainable in one context may be less sustainable when looked at in another – for instance, hybrid cars.

In the case of hybrids, the answer appears to lie with close study of life-cycle assessments. But what about products which don't have a clear life cycle? Or practices like recycling, which is generally sustainable but not in every case? What about complicated industries and supply chains, like those surrounding biofuels?

I understand that in many cases, whether a system is sustainable or not depends upon how the system is defined. So who defines the systems in question?

In general: how is the sustainability of a product or practice determined, and by whom?

Answer 1

By opposition, what is not sustainable is unsustainable. So that is what makes, for instance, in a closed system, something uses more energy than it gives some back. (It's like if you were spending more money than your incomes, that can't be sustainable)

To me, at least, sustainability is only defined by us like being the thing the less unsustainable as possible. You could also consider that as some kind of optimization (like in coding).

As far as I know, this isn't generally something defined officially (even though it's very likely that it has also been defined this way) so that there isn't really some people out there deciding for us what is sustainable or not. It's often pure common sense and abuses of language, otherwise or/and when you feel the need to clarify from which point of view we are talking, just go ahead and precise it.

Sustainability should be taken as a whole. When it's only from a point of view, just take that for what it is, another point of view to help you to build your own vision of the whole thing (This also depends on which importance you give to this point of view, all don't worth the same from one person to another (a bit like taste and color)).

Sorry, I know my answer is a bit fuzzy. Apologies. But I had to give it a shot. Hope it helps.

Answer 2

I don't think a definitive answer can exist.

I don't think we can ever say anything is defined other than from a point of view. One of the most important books on scientific epistemology (meaning theory of justifying scientific theories and the limitations of such) I can think of, Physics and Philosophy by Werner Heisenberg (yes, that Heisenberg), basically points out that even in theoretical physics, coming up with a theory involves essentially using unprovable/non-falsifiable assumptions to project meaning onto available data. As he puts it "data does not imply theory" or even one might say that scientific theories are products of our own assumptions at least as much as they are products of the data.

If that's the nature of things in theoretical physics (and I think Heisenberg is right there, and thus science thrives on uncertainty, pun intended), then it is true a even more in complicated questions like this one. These things are extremely complicated and there are no clearly defined boundaries between systems. The only really natural boundaries are those of the planet and those aren't very useful ones.

So when we talk about lifecycle analysis or any of the rest of this, we are talking about what are fundamentally simplified models based on unprovable assumptions only some of which we may be aware of (something drilled into my head when studying computational environmental modelling in college). Thus I think these tools are conversation-starters, but they don't definitively define what is sustainable. Certain there are things we can say are probably not (corn ethanol as a fuel source) and other ones have the jury out.

So in the end, what I would propose is that rather than seeing a definitive answer as to who we should trust to make these definitions, we must be responsible for such definitions ourselves.

So to the extent that an answer is possible, sustainability must be defined by each of us and all the models of the experts must be seen as conversation-starting pieces of the puzzle but in no way the complete picture even of a narrow topic.

Answer 3

Ultimately nothing is sustainable. Entropy increases. Eventually the sun goes out.

Ecologists refer to the 'carrying capacity' This is the amount of a resource in an ecological cycle that can be extracted without making a significant difference to the overall system.

The trick is that word 'significant'

So, for example, if you plant a forest on new land, it will initially not sequester carbon very fast. The trees are small. Then it will sequester rapidly, tying up carbon in wood mass. When the forest reaches climax, it no longer increases it's carbon mass. -- wood and leaves are rotting/being eaten as fast as they are growing on a year round scale.

I did the calcuations for my local poplar forest, estimating the total biomass at around 100 tons per acre. The maturation time of an aspen poplar forest is around 60 years in our climate. That gives me a 1.6 ton/year gross production over the life cycle of the forest.

So by one measure, I could extract something like 1 ton of biomass from the forest per acre per year, and do this indefinitely.

So that could be considered sustainable.

But wait: I take that wood away, and burn it or make chip board or fence posts (bad idea, rots to fast) and with the celluose I'm taking small quantities of Phosphorus and potassium.

Indeed: places where they have done intensive forestry, after about 3 generations of trees being removed, they have problems with mineral deficiencies. (That's removing something like half the biomass each time.) (Source Forestry Practices course 40 years ago in college.)

So if I'm burning wood for heat and return the ashes is it sustainable.

Maybe. That wood ash has calcium converted to CaO which reacts with water to make Ca(OH)2 which is quite alkaline. While sustainable in the sense that I've closed the cycle, it may make some radical changes in the soil chemistry.

It is no longer the same ecosystem.

Perhaps it would be better to estimate a 'sustainability' factor. How many times can this operation be repeated (or years) before the measurable impact occurs.