Here is how I put it in a letter to my sister, who works for a coal-intensive electric utility:
Whew! Needless to say, the letter had little effect. But to expand a bit, what realizing a sustainable future will take is not only consciousness-raising, but also a high intellectual level of personal cultivation and cultural discussion. To have rational foresight centuries and millennia into the future, and to value those future inhabitants of the earth takes both great insight and great imagination. There is no time to lose. This is surely no time to be debasing our discourse and dumbing down our children, as seems to be the primary aim of much organized religion.
There is a large paradigm shift underway, from the primeval conviction that nature is infinite, our place minuscule, and our effects minor, to a realization that the planet is finite, and that we are deranging the biosphere in major ways. Everyone except the current administration sees the reality of global warming. So the issue becomes one of how to calculate the costs we are imposing on future generations and incorporate them into our current choices. The extinction of the arctic ecosystem... the "fishing-out" of most large ocean fish... the eventual loss of all large rain forest species (such as the apes), and most smaller animals.. the mysterious disappearance of most amphibians... When you take a thousand year, or 10,000 year, or beyond perspective, these are incalculable costs. I can not say how this generation will be damned by the future for despoiling their world, but the costs are clearly not showing up on any one's balance sheet yet. To say that we should do only what is easy, satisfying our greed now and leaving the future to fend for itself seems deeply wrong if we are unalterably changing the world they are to inhabit.
We know a great deal about the bounds of what that future will hold. Life will go on in any case. If we kill off the rich diversity of animal species, the microbes will persist in their vast profusion in any case. We are also in little danger of killing ourselves off. If we turn the whole earth into a farm, the oceans into a microbial soup, and the air into a miasma of pollution, people will find surely some way to survive, and in large numbers. The question is what kind of existence that will be. It is also completely implausible to expect to live anywhere other than the earth. No other planet is habitable on any practical basis. In fact, this would be a good time to add my critique of the administration's Mars policy, which sacrifices the high-tech robotic exploration of space, which has been spectacularly successful, as well as being an engine of positive economic benefits, to the idiocy of manned trips to places we do not need to send people, and for truly astronomical costs. The impracticality of getting to Mars, let alone living there, is monumental. So, though I am as much a Trek fan as anyone, I have to say that the physics of the situation places our long-term and exclusive home here on earth.
What all this boils down to is an imperative to move quickly to a more sustainable way of living, both in terms of the overall number of people, and in the per-person cost of inhabiting the earth. The motivation is more aesthetic and moral than it is any problem of absolute self-preservation, but man does not live by bread alone, and should aspire to live on a beautiful earth, not a degraded one. My view of the environmental and sustainability issue is that we have big choices to make now in order that future generations can live decently and in a nature that nourishes them in spiritual as well as physical ways. Otherwise we can live in a Blade-runner or other science fiction dystopia. The rest of the world is willing, through the Kyoto process, to make baby steps in that direction, and it is shameful that we are not willing to join that process.
It is thought that early people contributed to the demise of many big animals through over-hunting. The field is controversial, but at any rate, we generally forgive them because they did not have the knowledge and consciousness we have today. We will not have that excuse vis-a-vis future generations. We know full well that we are doing irreparable harm to the biosphere. In economic terms, it is a tragedy of the commons, since the current institutional system pays little attention to the "external" costs of general environmental degradation. Pleading that we should only do what is convenient is not looking the problem in the face. Unfortunately, since the economic incentive system is so poorly designed, it falls to those who regard the issue in moral terms to call for greater action. This kind of moral persuasion is weak enough, but I believe it is at least right.