This is kind of funny--from Robert Frank's defense of carbon offsets in today's New York Times:
Yet carbon offsets have drawn sharp criticism, even ridicule. A British Web site called Cheat Neutral (www.cheatneutral.com) parodies the concept — by offering a service under which someone who wants to cheat on his partner can pay someone else who will refrain from committing an act of infidelity.
Frank goes on to explain why the analogy isn't quite apt. And while he's right, I think he's being a bit literal about it. The wags behind Cheat Neutral do get at a larger absurdity.
I guess it comes down to how you feel about pollution--or, at least, gratuitous pollution (that is, pollution with no obvious economic or utilitarian benefit--like buying an SUV just because you like the look of it, not because you need one to navigate tough terrain). If it's immoral to pollute gratuitously, then buying an offset doesn't somehow make it better, any more than buying a papal indulgence or an infidelity offset wipes away a sin. But if the only problem with polluting gratuitously is that it results in pollution, then Frank's right and the offset conceit is fine. I guess I'm inclined toward the former view. It doesn't surprise me that an economist would tend toward the latter.
Update: Just to be clear, I'm not saying that gratuitously polluting is morally reprehensible--I'm sure I do it on a regular basis. I'm just saying it's a net moral negative, and you can't erase that moral negative with a carbon offset.
Update II: Brad has some additional thoughts over at The Vine. I don't really disagree with anything in his post, which makes me think I should clarify one more thing about mine: I think the biggest problem with pollution is its negative practical effects. So I agree with Brad and Robert Frank about that. I'm just saying there's a moral dimension, too--at least to polluting gratuitously (which is a squishy thing to get at in practice, but easy to understand in principle). My point is that, while a carbon offset solves the practical problem of pollution--which, again, is by far the bigger problem--it doesn't do anything about the moral problem. In the same way that, I dunno, an abusive parent can't wipe away the moral trangression of breaking their kid's arm even if they pay to fix it and solve the practical problem of the child not being able to write and play sports, etc.