Good news for green-inclined travelers today, online-travel giants Travelocity and Expedia are adding the option to balance out the greenhouse gases produced by flights, rental cars, even the average hotel stay, to their checkout pages. “Zero footprint” programs of this kind have existed for a while, but streamlining the choice to offset into the reservations process seems like such a simple and smart way to ensure that more people will take advantage of them. Travelocity has partnered with the Conservation Fund to turn $10-$40 donations into enough new trees to absorb that last trip to Europe. Expedia is taking a different route, allowing users to pay a fee, between $6 and $30, that will fund TerraPass, an organization that supports research efforts into alternative energy sources such as “wind farms, [and] innovative ‘cow power’ methane capture plants on American dairies.” In both cases a small amount of cash translates to a big result: just $30-$40 offsets enough carbon dioxide to compensate for 13,000 miles worth of flights, or a long-weekend package vacation for a family of four.