"Offsets are not going to solve global warming," says Dale Bryk, a senior attorney at the National Resources Defense Council. "We need mandatory caps on pollution, and policies that drive innovation in biofuels and energy efficiency." Offsets can complement regulation, she says, but only if we choose them carefully. Does your money go to a specific project? Can the provider show that the project will produce new offsets rather than support those already in the pipeline? How long will it take for the offset to accrue—years? decades? "There's currently no objective standard or certification process, so you can't buy in confidence unless you thoroughly investigate what type of offsets a company is selling."

No matter how you look at it, there's an environmental toll to be paid for flying, just as there is for driving or for heating and cooling our homes. But as Bryk points out, there may also be an environmental benefit. "Traveling to places such as Indonesia and meeting those who will be most hurt by global warming might make people glad to pay an extra two dollars on their electric bill to fund clean energy."

Maybe we're part of the solution after all.