A FedEx employee sorts boxes on the sidewalk on Nov. 21, 2019, in New York City.

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At a Glance

New research shows online shopping generates more pollution than going to the store.The results could vary in places where people are more likely to bike or walk to shops.U.S. consumers spent $158 billion shopping online during the last quarter of 2019.

Online consumers might think they are helping the environment by not driving to the store, but researchers say that's not always the case.

A new study in the journal Environmental Science & Technology found that shopping in a regular brick and mortar store often creates less greenhouse gas emissions than shopping online and having packages delivered to your home.

That's because most people only buy a few items at a time online, and then those items have to be packed and transported, sometimes from different distribution centers. Packages often arrive with only one or two items in the box, or people make small purchases separately online instead of all at once.

"When they shop in a store, they aggregate these purchases ," Sadegh Shahmohammadi, a doctoral student in Environmental Science at Radboud University in the Netherlands and one of the researchers, told CNN.

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Frequent online purchases also produce more packaging waste, Shahmohammadi added.

The study, conducted in the United Kingdom, looked at "fast-moving consumer goods" such as toiletries, cleaning supplies and packaged foods, and focused on the carbon footprint of what's known as the "last mile" in the supply chain process: the distance between a store and a customer for brick and mortar shopping, or between a distribution center and a customer in the case of online shopping.

The results showed that greenhouse gas emissions were higher for online shopping 81% of the time. The study conceded that results could vary in places where people are more likely to bike or walk to shops.

"This pattern holds true in countries where people mostly drive," Shahmohammadi told CNN. "It really depends on the country and consumer behavior there."

generated similar results.

But Americans aren't likely to give up their click-it-and-ship-it habits anytime soon.

The U.S. Census Bureau estimates that e-commerce sales racked up in revenue for the fourth quarter of 2019. A 2018 NPR-Marist poll showed of Americans said they had purchased something online at least once, and 43 percent said they regularly shop online. Reflecting the demand, UPS, FedEx and the U.S. Postal Service now deliver packages seven days a week.

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