"Seems like a tough sell, but it's the latest rage in travel. About 50 companies and organizations, profit and nonprofit, have sprung up in the past couple of years to sell not something, but the absence of something -- greenhouse gases, to be exact".
This article in the Washington Post details an interesting new trend. Now consumers can pay carbon offset providers to calculate the greenhouse gases created by national or international flights and plant trees to offset those emissions.
"Here's how it works: A carbon-offset provider, using a calculator programmed to make certain assumptions, figures that a plane traveling between Washington and San Francisco will spew into the atmosphere, say, 90 tons of carbon dioxide, to choose one of many disputed estimates. If there are 180 people on that flight, then you're "responsible" for half a ton of those emissions. You pay the carbon-offset provider, say, $10, and it'll use the money to reduce the same amount of carbon somewhere else".