There is the fact that it is possible to treat something badly or to damage it, whether or not it is sentient. A pair of shoes can be badly or well looked after, and it is wrong not to look after a good pair of shoes properly. A living thing like a hedge can be properly maintained or attended to, but something more is involved. Sometimes, it seems to me, the aesthetics of the "art object" (horrible phrase) can reflect what it actually is. So it is natural to trim a box hedge in one way, and a mixed hedge in another way, perhaps a less formal and more undulating, the shapes reflecting the different kinds of growth - hawthorn, or privet or beech. (A hedge that is full of straggly and unwanted sycamore looks awful, and the holes soon begin to show.) Pugs and poodles may be perfectly happy qua sentient beings, though often there are specific health problems with specific breeds, but it is perfectly coherent to object to the whole process of breeding and thinking of living things as being objects for our use - manipulation - and enjoyment only. Much the same comments can be made about the wilderness, and your question and suggestion raise profound and important questions of ecological ethics and aesthetics. For some, the ethics of GM foods has a spiritual dimension too.

If "natural" means "part of nature broadly conceived," then it's hard to see what's uncontroversially not natural. But what this really shows is that there is mre than one meaning of "natural" and more than one contrast that someone might make.

Someone who believes that the material world was made by an immaterial creator would contrast the natural with the supernatural. On that usage, more or less everything in space and time would count as natural.

But someone might also have the distinction between natural and artifactual in mind, and if that's what they mean, then my computer is not natural, but the flower on my windowsill is. No contradiction here; just a different distinction. As for what makes something an artifact, that's not easy to say with real precision. But it's easy to come up with a wealth of examples that more or less everyone will agree to. (The fact that we can't articulate a distinction doesn't show that we can't make a distinction.)

There's another notion of "natural" that's broadly teleological. It makes most sense, perhaps, if we assume that there is a designer who made the world according to a providential plan. On that way of lookng at things, we and various other parts of the world were endowed with natures that, when working properly, contribute to the providential order. On such "natural law" views, what distinguishes humans from animals is that we can choose to act contrary to our natures. Thus, a natural law theorist might say that we were endowed with reason, and that to ignore our reason is to act contrary to our providentially-ordered nature.

There are non-theological analogues of this distinction that appeal to something like biological function. Unfortunately, the moral weight of theological notions of divine order sometimes gets carried over into the non-theological context, and leads people to say that, for example, homosexuality is wrong simply because homosexual sex is "unnatural" by virtue of not serving reproduction.

Someone might also say that a biological process gone awry is not natural. And in fact, it's interesting to note that we can all think of examples of what we'd count as "biological processes gone awry." Whatever weight we put on the associated notion of "natural," it doesn't seem merely to be empty.

So there's no one thing people mean when they use the word "natural." And so whether something counts as natural will depend, among other things, on what notion of "natural" is at issue.

I suppose we have the right to sponsor the sort of environment we favor, other things being equal, and where species live off each other we have to accept that there will be victims and there will be victors. Introducing a new and dangerous species seems wrong unless it has some practical benefit, or was designed to save it from an imminent disaster. Wiping out a species irretrievably reduces variety, and there is no reason why we should not value variety in our idea of an environment and seek to foster it, perhaps for aesthetic reasons alone.

Not necessarily. It is only worth saving things that are worth saving. One would need to have a view on whether a particular species was good to have around, serves any useful purpose or is an obstacle to the welfare of what we regard as important species, like us. Otherwise our attitude to nature would be like the attitude of those deranged individuals who never throw anything away because "it may come in useful one day". Indeed it may, but it is more useful not to have trash all over the house.

Imagine someone who thinks that wild things ought to be preserved and protected -- that it is humanity's moral duty to do so. She might even be one of those good people who manages to put these "green" moral principles into action. But suppose that she does not especially enjoy being around natural things. She might well prefer "civilization" to "roughing it", and she might not even find baby seals especially cute and cuddly. Perhaps she does not even derive any pleasure from the thought that there are wild places. They may leave her utterly unmoved, or they may even inspire in her fear and terror. (An astronaut might feel that way about the surface of the moon.) Such an individual might be described as respecting nature without liking it a whole lot.

By the same token, imagine someone who likes nature. She enjoys spending time in wild places and derives deep pleasure from her interactions with wild things. To find opportunities to commune with nature might even be one of her main lifelong pursuits. She might be as strong of an advocate for the national park system as the first person I mentioned, but simply because she would like there to be parks for her to enjoy, not because she feels any moral duty towards nature. Suppose that there is no moral component at all in her attitude toward nature. She does not think that nature is valuable in any objective or transcendent sense. She may take nature to be valuable to herself, since it is something she likes, but she does not believe that nature is somehow valuable in itself. She simply likes nature, just as I like ice cream but do not think that someone who is indifferent to ice cream is morally blind. Such an individual might be described as liking nature but as having no particular respect for nature.

This is a fascinating question, in some ways, I think, it's connected to the question of whether we have responsibilities to things bigger than us in the sense of things that can continue to exist without us--e.g. things like families, nations, political and artistic movements, cultures, universities, businesses. Generally, I would say there is a moral obligation to sustain good things generally--at least where sustaining some good thing doesn't require undermining another of greater value.

To your specific question: I would say that considering the species itself, there is no obligation to sustain it, since the simple existence of the species is neither good nor bad, so long as there are other species to substitute for it. Considering the species as part of the larger ecosystems of the planet, where genetic diversity is salutary for the health of living things generally, there is an obligation insofar as the well being of living things is good. Considering the existence of the species as the necessary condition for all kinds of other goods, such as art, science, scholarship, virtue, culture, family, sport, etc., implies that an additional obligation exists as well. Of course, this last bit does depend upon the idea that the goods that the existence of human beings makes possible are not overwhelmed by the bad things their existence produces.

The eventual demise of humanity seems inevitable, so that mere prospect doesn't seem noteworthy. That our activities cause some damage to other things also seems inevitable.

Surely, however, we are responsible for enviornmental damage that we cause. Even if some damange is unavoidable, we can--and should--find ways to minimize this damage here on earth or wherever else we find ourselves.

Preparing for emigration off-world seems a hasty response to me, but not because we are likely to destroy celestial bodies. Rather, Hawking's conclusons that there is nothing we can do to avoid an environmental catostrophe here on earth seems hasty and counter-productive: we don't have the technological and financial resources to move the population to another world, but do have the means to reduce the damage that we are doing to this planet. Therefore, I would think we would be wise to focus on that.

There are many interesting philosophical questions here. For example, when assessing the environmental damage that we cause to what extent and how should we consider the interests of non-human life or even non-living things? Should we consider the interests of unborn humans or other things that do not yet exist, but might? Finally, how strong is the obligation to act to prevent an envirommental catastrophe? For example, do we have moral obligations to the enviroment or to nature that trump obligations we have to other humans? For example, is it okay to act injustly to one another if we determine that this is necessary to prevent a large-scale environmental catastrophe?

Philosophers can bring reflection on the responsibilities that contributors to global pollution have toward foreigners, future people, and animals and the rest of nature.

Foreigners. Global warming is likely to cause severe harms to foreigners -- from draughts in Africa to flooding in Bangladesh -- especially to foreigners who are poor and vulnerable (who, for this reason, are themselves only very minimal contributors to global warming). Most of us shrug off the thought that we owe them anything. We think it's alright to pollute or that our individual contribution is too small to matter. Is this an adequate response if millions die prematurely as a result of the pollution we together produce?

Future people. Global warming is likely to have devastating effects far in the future. In cost-benefit analyses, it is common to discount the interests of future people, typically by 3 percent per annum. This is thought plausible in analogy to how individuals discount future pains and pleasures -- we are much more distraught when we face death tomorrow than we when face death in 40 years. But is the discounting of future people really plausible? Are deaths in 23 years only half as important, and deaths in 53 years one-fifth as important as deaths today? Is one human death today the moral equivalent of 500 deaths in 204 years, ... of 300,000 deaths in 414 years, of 17 trillion human deaths in 1000 years?

Animals and the rest of nature. Global warming may wipe out many biological species and destroy places of natural beauty. Do these losses have any disvalue beyond the significance they have for us? Or are we human beings permitted to destroy all these beings and places so long as we are ready to do without them?

Best for whom? The enviroment may change so that a particular species of tree is no longer very successful at propagating itself. If we do nothing, it will go extinct. But it might be much better for us if we did not let that happen, because the bark of the tree contains a chemical that is highly beneficial to us.

Life is complicated, sure enough...

My advice (for what it is worth--not much, I expect) is for you to hang on to your job. Partly, this is precisely because you quitting your job (unless you have some other very clear option available to you in a "clean" occupation) won't make the least bit of difference to the project of ending waste, for the very reasons you gave: someone else will do it, and all you will have done is put yourself out of work.

Instead, why don't you consider--and urge your colleagues to consider--"greener" practices at work. For example, designs done on computers (rather than sketched on paper) create less paper waste. (An out-of-date example, I'm sure, but I hope you get the point.) Those with expertise in an industry are in the best position to find ways to cut waste and to come up with processes (and products) that are not so bad for the environment. Find these!

And where you can't find better solutions, consider finding "compensations" such as planting more trees at your place of work--or contributing trees to plant in local park areas, or somewhere else in the world--and so on. Quitting your job may seem very noble and clean--but the reality is that you are likely to end up doing something just as bad (or possibly worse), and if you stay, you may be able to make a positive difference.