Amadeus, the airline IT and GDS vendor, plans to integrate data from the International Civil Aviation Organization's carbon calculator in all of Amadeus' reservations platforms my mid-2010.
In the announcement [pdf], Amadeus notes that more than 1 million passengers fly daily after booking their flights through reservations processed by Amadeus. So, that's a lot of travelers who may at least be reminded that -- regardless of the flight deal they may have found -- air travel comes at an environmental cost.
In fact, the ICAO estimated that in 2007, aviation accounted for 2% of the world's greenhouse gas emissions.
I'm kind of doubting that Amadeus' integration of the carbon calculator amounts to saving the world with technology, but it can't hurt.