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.