Guilt-free flying for $88?

Air NZ has introduced a voluntary carbon levy.

Air NZ CEO Rob Fyfe said:

"When customers purchase a flight on Air New Zealand, they will now be able
to make a concious choice about whether or not they want to take positive steps
toward helping our environment."...

Prime Minister Helen Clark said at this morning's launch the airline had set
itself the "bold goal" of being the world's most environmentally responsible
airline.

I wonder if Air NZ has calculated the "environmental cost" of its flights. Underpinning any such work will be a stack of assumptions, many of which I expect are debatable. However, nit-picking aside, this raises the question in my mind as to why they did not impose a levy across the board (in the same way the airlines have imposed levies for fuel costs). The intuitive answer is that by being the first to do that would lose them market share.

Given the investment in carbon credits and the investment in for an "environment trust" (whatever that is) Air NZ is already bearing some of the cost of its emissions. And presumably that cost is being borne by either passengers and/or shareholders.

Being a cynic by profession, upbringing and experience, I can't help but wonder if this move is expected to actually generate significant revenue for the trust or simply a publicity stunt.