Every single day this December, an estimated 1 million return packages were picked up through UPS alone, and online shoppers are expected to send back even more purchases this holiday season.

Each returned package — regardless of which carrier picks it up — leaves a trail of emissions from the various trains, planes, and giant trucks that carry it back to the seller. That pollution contributes to climate change and worsens air quality. Many of the discarded items head to a landfill. The environmental problem is only getting worse as e-commerce grows and free returns become the expected norm for shopping online.

Each returned package leaves a trail of emissions

The biggest flood of returns will come on January 2nd as people head back to work after the holidays, when UPS expects to handle nearly 2 million return packages. That’s a more than 25 percent jump from the packages it handled the previous year on January 2nd, which UPS has dubbed “National Returns Day.” Amazon, which has driven the new shopping trends, just expanded its free return policy and is also delivering more of its own packages than ever. Luckily, there are things both individuals and companies can do to cut back on the boomeranging packages.

Retail consequences

“People need to be aware that there are environmental consequences of sending back their returns. You know, they don’t just go into thin air and disappear,” says Sharon Cullinane, a professor at the University of Gothenburg in Sweden. She began researching what happens to clothing returns after a visit to a warehouse with her students; there, they came across a big pile of shrink-wrapped items in a corner. When she asked what was in the pile, she says she was told: “Those are the returns. Because we don’t know what to do with them, we call them the ‘uglies.’“

About half of the “uglies” that American consumers return go back on sale again, according to research by Optoro, a company that helps retailers like Ikea streamline their returns processes. Retailers might send things back to the manufacturer that they can’t put up for sale again, or they might try to unload it to other companies who sell it at deep discounts.

Wherever the unwanted purchase goes, taking it there means more trucks pumping out more planet-warming carbon emissions and other harmful pollutants. Hauling around returned inventory in the US creates over 15 million metric tons of carbon dioxide emissions annually, Optoro found. That’s more than what 3 million cars might put out in one year.

Five billion pounds of returned goods end up in US landfills each year

Then there’s the trash. Five billion pounds of returned goods end up in US landfills each year. Even if something was in good condition when the buyer put it in the mailbox, shipping it back can damage the item. Sometimes retailers realize that throwing out a returned item is the most cost-effective way to deal with the thing, instead of paying for it to be cleaned, repaired, and returned to the shelves. “If you’re buying a T-shirt or something like that and it only costs a few dollars, you can understand that the company just cannot afford to do anything but throw that onto the landfill,” Cullinane says. Landfills are filling up with packaging waste from e-commerce, too.

Return revolution

If customers want to reduce the environmental impact of their returns, there are a few things they can do: Return items sooner. Waiting until the last minute to send something back increases the chance that the item won’t go back to stock for resale (especially for holiday-themed items that are returned after the holidays)

Take items to a collection center for returns, like UPS offers, instead of mailing it off

Order just what you need, instead of buying multiple options with the intention of sending some back

The amount of purchases being returned is climbing and there are spikes after Black Friday and Christmas, Cullinane tells The Verge. That’s thanks in part to the rise of e-commerce. E-commerce has a higher return rate, 20 to 30 percent according to the National Retail Federation, compared to other kinds of purchases (auto parts and consumer electronics trail behind with a roughly 20 percent return rate). Offering hassle-free returns has been a big part of encouraging customers to buy something online that they’ve never actually seen or touched in real life. But that’s led to people buying things just to try something out and return it later. “They’re basically using their home as the changing rooms,” says Cullilane.

Companies that have encouraged these changes in consumer behavior can take steps to minimize returns and make the process less harmful when someone does send something back. For one, they can make sure that the way they market their items online is true to what the product is like in real life. Giving more detailed information on sizing for apparel is helpful, too. Plus more and more brands are offering ways to let prospective shoppers try stuff on virtually.

Advocacy groups like the Environmental Defense Fund are also pushing for companies to electrify delivery vehicles, especially along what’s called “the last mile of delivery.” The last mile refers to the trip from a warehouse or distribution center to someone’s front door (or the reverse, in the case of returns). Warehouses have been popping up closer and closer to neighborhoods in order to meet the growing expectation for fast deliveries, and that means that the air pollution from e-commerce is creeping closer to peoples’ homes. To lessen the environmental and health harms along their supply chains, companies can replace diesel-burning trucks with zero-emissions vehicles. Ikea said that it will start offering zero-emissions delivery in five major cities in 2020. Amazon announced in September that it would order 100,000 electric delivery vans.

a new trend: customers caring about how their purchases affect the planet

Taking those steps makes business sense. Not only can companies save money on costly returns, they can also cater to a new trend: customers caring about how their purchases affect the planet. “You’re inviting a company or product into your home; it’s sometimes a personal expression of your identity,” says Aileen Nowlan, a senior manager at the Environmental Defense Fund. “Consumers are increasingly really caring about all the implications of those decisions.”