The idea of sustainability is one of the more popular concepts in environmentalism (perhaps because it is anthropocentric -- i.e., it doesn't make any unpopular claims about the inherent moral worth of non-human beings and systems -- while justifying wide-ranging environmental protection). In essence, it states that we should leave sufficient resources for future generations to live. The first question this raises is how much future generations need. Should we make sure they have just enough to survive? That doesn't seem very kind, and it leaves us with a fairly anemic form of sustainability. What about leaving them as much as possible? This is an unpalatable sort of call to self-sacrifice. And it's self-sacrifice for a group that will not benefit from it -- if the next generation maintains this strong sustainability principle, it too will sacrifice its use of nature for the following generation's potential benefit. At best we can enjoy non-consumptive values, such as aesthetic pleasure or clean air for breathing (but not clean air as a pollution sink). What's necessary is a commitment to some form of minimum quality of life standard that future generations are entitled to, and thus to providing sufficient resources to attain that standard of living.

This leads us to another problem: we don't know what resources future generations will need. A resource is socially constructed -- it is only a resource if people want to use it for something. If future generations' uses of the environment were to stay constant, we could more easily ascertain what resources they will need. While this may be a reasonable assumption for a society that changes fairly slowly -- such as pre-contact Aboriginal Australians (though even Aboriginal society changed over time, incuding some potentially quite rapid changes) -- it does not work so well for our modern dynamic society. We can't be certain what inputs and sinks our progeny's preferred productive and consumptive activities will require. The form of society matters as well. It takes fewer resources to maintain a given standard of living if they are distributed equitably than if most of them are monopolized by a few members of society.

There's yet another complication: the availability of resources affects the shape of society. Had (to pull out a bizarre hypothetical) the Mongols torched the world's oil reserves, assuming oil was not a resource, we wouldn't have developed into an oil-dependent economy that's really in trouble because there's no oil. We would have developed a different technology. We should be careful of being too adaptational in our thinking, lest we wind up assuming that future generations will be able to make do with whatever we leave to them. But it does suggest that perhaps the solution lies in our ability to adjust both sides of the equation. This possibility is bolstered by the fact that the next generation is not some separate phase of human activity. One generation does not pass from the stage before the next comes along. It's a rolling process. This opens the door to short-term resource management and adjustment. However, I've now set myself up for yet another problem: without some sort of long-range view, we can't tell if we're carefully walking into a dead end.