IN TRANSIT: AMSTERDAM -- Delta Air Lines announced on Wednesday that it would become the first airline to implement a "voluntary carbon offset program" for passengers feeling guilty about the carbon dioxide emissions of their flights. Starting June 1, passengers who book their tickets through Delta.com will be able to make small contributions ($5.50 domestic/$11 international roundtrips) to The Conservation Fund, which will plant enough trees on your behalf to soak up the CO2. Delta is also making contributions on behalf of every passenger who flies this Sunday, Earth Day, although I don't know for how much.

Delta isn't the first airline to realize the marketing angle of going green (that would be Silverjet, which builds the price into your ticket), but it won't be the last. I have a running argument going with my friend Andrew, who can make a pretty persuasive case that a backlash is brewing in the U.S. against the environmental impact of air travel. When the director of airport development here at Schiphol tells you that emissions and sustainability are the gravest concern facing the airport (even ahead of noise, the previous great bugaboo) you have to take those arguments seriously. But I refuse to believe that either Americans or Europeans would seriously hamstring the lifelines to the iPods and Toyota Prius engines being manufactured in Asia and airshipped over here. Still, why not offer passengers a chance to assuage their guilt and make your airline look good in the process?

My only question is who is accounting for the donations in question... and how? Delta has vowed that "100%" of donations will be passed along to The Conservation Fund. Assuming it catches on, I wonder how long it will be before a chunk of those donations are earmarked as "processing fees," and how long after that before those fees start dropping right to the bottom line.

Read more of Greg Lindsay's travel blog, IN TRANSIT.