The question about moral obligations to future generations is sometimes approached in a backwards manner. In those instances it is simply assumed that we must have some moral obligations to future generations, and if a moral theory leads us to think that we do not, then there must be something wrong with the theory in question. This is, as I said, a backwards way of doing ethics, since the question about about future generations is all about application. To apply a theory we must first know what theory we endorse, not the other way around.
Now some people reject utilitarianism, since – they claim – utilitarianism cannot account for our moral obligations to future generations. I think that is a bad reason to reject utilitarianism. If one wants to reject it, one should argue against the theory itself and not make it stand or fall with one particular application of the theory. But destroying utilitarianism as a theory does not, of course, establish that we do have duties to future generations, because that should be defended as an application of a different theory, and not simply assumed.
But is it actually true that utilitarianism does not entail obligations to future generations? My answer would be no, at least not when it comes to the type of hedonistic utilitarianism that I endorse. It is true that this kind of hedonism sees no value in maximizing the pleasure of people not yet born. I believe in maximizing the pleasure of people who live right now. This is, thus, a kind of average utilitarianism, and it differs from “total” hedonism in that we can’t just make more and more babies to raise the sum of happiness (provided that the new babies will have lives that are more on the pleasure than on the pain side of the spectrum – lives “barely worth living” as some would say). By the same token we do not have to care about the potential pleasures of those unborn people.
In theory, the average view might advice us to simply use up all the world’s resources to enhance the pleasure of the people living right now. And if this was the last generation living on earth this would surely be the right conclusion. But as soon as a new baby is born, its pleasure must matter to us. If we can expect that this baby will live to the age of eighty, then we must at least make sure that her or his quality of live does not diminish sharply when our own generation is gone. Right, you might say, but do we only have to care about one generation after us? I would reply that this is no small thing. Since new babies are born all the time the horizon of obligation keeps moving forward at the same rate. Whatever point in time we pick it seems that we must always make sure that the world will be a hospitable place to live 80-90 years from now.
So while it is wrong to claim that hedonism implies obligations to future generations (if by this we mean unborn generations), it still implies an obligation to provide a good future for newly born generations – which, as argued above, is a constantly moving target. And it does imply robust protection of our environment, at least until we all perceive that the planet is doomed and we deliberately stop procreating (or move to another planet). This should, however, not be a decisive reason for an environmentalist to endorse hedonism. As I see it, environmentalism is applied ethics (unless we are talking about “deep ecology” and the like), which means that one should first decide which ethical theory is most reasonable, and then let the theory lead one to whichever conclusion on the environment that the original premises warrant. It seems kind of intellectually dishonest to start with the conclusion and then construct the premises.