E-scooters have a very environmentally-friendly image. Tiny and battery-powered, they seem like a convenient, responsible alternative to making short trips in a car, but new research suggests that the big picture is a lot more complicated.

A team of researchers from NC State took an in-depth look at the overall environmental impact of the e-scooter trend, examining the emissions output associated with building, shipping, and charging the scooters, as well as the travel habits of individuals who often use them. The results paint a troubling picture of the seemingly green transportation option.

E-scooters themselves are zero-emission vehicles, and that’s great. However, as the researchers explain, the manufacturing process that actually produces the scooters is far from pollution-free, while shipping and distribution of the scooters adds even more to their carbon footprint.

But perhaps the most striking thing the study reveals about the e-scooter trend is that the majority of those who rely on them for their transportation needs aren’t doing so in lew of a car ride. In fact, in a survey of e-scooter riders, the team found that 49 percent of them would have biked or simply walked if the scooters weren’t readily available.

The most damning aspect of e-scooter proliferation seems to be the fact that companies rely on other vehicles — gas-burning trucks and vans — to collect the scooters and redistribute them to the locations where they are picked up by users.

“We found that the environmental impact from the electricity used to charge the e-scooters is fairly small – about 5% of its overall impact,” Jeremiah Johnson, co-author of the study, said in a statement. “The real impact comes largely from two areas: using other vehicles to collect and redistribute the scooters; and emissions related to producing the materials and components that go into each scooter.”

Put simply, e-scooters may be an Earth-friendly alternative to firing up your car for a trip to the store, but walking or biking proves to be a far more environmentally conscious.

Mike Wehner has reported on technology and video games for the past decade, covering breaking news and trends in VR, wearables, smartphones, and future tech. Most recently, Mike served as Tech Editor at The Daily Dot, and has been featured in USA Today, Time.com, and countless other web and print outlets. His love of reporting is second only to his gaming addiction.