It's probably worth noting that economists are also familiar with something called "collective action" problems; have probably noticed that individuals cannot, themselves, end global warming by purchasing a moderately large quantity of carbon offsets; and so would find it perfectly rational and utility-maximizing that individuals concerned with stopping global warming spend their time creating political pressure for a collective -- and thus effective -- solution, rather than ineffectually lowering their personal output.
One could argue, incidentally, that every time Al Gore is called a hypocrite, is efficacy is marginally reduced, and so he should indeed spend every spare penny buying offsets that won't actually solve any problems because they are useful for his political image which is in turn useful for his advocacy which in turn helps speed legislative action. But buying individual offsets is more an innovation in personal political validation than carbon reduction -- it lets you say something about who you are, but it doesn't solve any problems, nor even come close.
