For many Americans, air travel is their largest source of greenhouse gases. One international trip can be the equivalent of a year's worth of driving. So what is a responsible climate-citizen to do? Of course, you could stay home, but what's the fun in that? Sustainability doesn't have to be about not having what you want; it should be about finding sustainable ways to get what you want. This article has several suggestions and mentions which airlines offer carbon offsets and use biofuels.