Here I want to add another example. Suppose I think that it's wrong to eat animals and animal products (as in fact I do) but that I really like the taste of meat. Could I discharge my moral obligation (as I see it) to be a vegan by continuing to pack away the hamburgers and steaks but pay a carnivore to convert to veganism so that I "meat balance?" The very idea seems absurd.
But I've been wondering whether this sort of comparison is unfair to Gore. Perhaps his real mistake was in referring to global warming as a "moral issue," and thereby implying that each of us has a moral duty to future inhabitants of the planet. If global warming is just a policy matter, then all we should really care about is the bottom line. Or perhaps there is a species of moral actions that we should evaluate simply by our net impact. So that maybe it is morally permissible to buy one's way out of some obligations but not others. I certainly have the intuition that this is so. I also have the intuition that vicarious veganism clearly doesn't work, while vicarious carbon neutrality is closer to the line of the permissible. Another clear example: I can't discharge my duty not to commit murder by going on a killing spree and then saving an equal number of other lives. However, I am quite unclear about what exactly the criteria should be for deciding when a moral duty can be discharged by payment rather than directly. Or perhaps I'm simply wrong, and all duties can be discharged vicariously? (Don't worry; I'm not armed.)