By Dan Shapley
The travel industry is making a pitch to consumers who want to travel the globe, but feel pangs of guilt about all the carbon dioxide - not to mention high-altitude contrails - that trap heat in the atmosphere. On-line travel agents are leading the charge, offering automatic offsets for each ton of carbon emitted by a person's vacation. The surcharge on the ticket goes toward investments in renewable energy and the like, offering travelers a way to feel better about their travel plans. Critics wonder if both technology and vacationing habits will have to change, however, before travel can reach a sustainable level.