The season of giving is over. It’s followed by the season of returns. During the first week of January, US consumers will send nearly $30 billion in products back to where they came from, returning 9% of all e-commerce purchases. That adds up to 5.8 million packages in transit, peaking January 5th, a day that UPS has nicknamed National Returns Day. But here’s something you probably didn’t know: Many of those returns aren’t going to make it back into store inventory and onto shelves. Instead, they will rack up a giant carbon footprint as they wind their way through a network of middlemen and resellers and, at each step, a share of those goods will be discarded in landfills. “It’s a huge environmental impact,” says Tobin Moore, cofounder and CEO of Optoro, a technology company focused on improving the “reverse logistics” of consumer returns. “It’s over 4 billion pounds of [landfill] waste generated a year in the US from reverse logistics.” Optoro, which UPS recently bought a stake in (paywall), estimates that just 50% of returns go back into store inventory. Because of their condition, due to use, damage, or even just opened boxes, the rest have a different fate. Stores may be able to return some to their manufacturer, or resell them through their own outlets. But often they sell them at a fraction of their original cost to discounters or massive, centralized liquidators, who buy truckloads of inventory that they sort and resell to other middlemen before they land at secondhand shops. At each step, if it’s more economical to throw an item away rather than ship it, off to the dumpster it goes. Big retailers toss out huge quantities of inventory each year. Moore says that many people mistakenly think their return will simply be resold, so they use free shipping/easy returns to effectively rent products, like TVs for Superbowl parties or power drills for moving into a new home. Unfortunately, not everything you send back will have a second life. That’s something to think about next time you hit send from that virtual shopping cart.