Buying groceries and toiletries online can lower the carbon emissions from your purchase, but only if they’re delivered from a brick-and-mortar shop nearby, according to a new study from the UK. If your local grocer offers deliveries, that could have a smaller environmental impact (at least when it comes to planet-heating greenhouse gases) than driving to the store to pick them up yourself.

In contrast, buying the same products from an online market (like, say, Amazon) will contribute more to climate change because more emissions are generated when the items are shipped from a distribution center via courier.

The recent study adds to growing evidence that the environmental costs of online shopping are getting more complicated as online retailers drive new consumer habits. Online shoppers can minimize their impact by bundling their items and purchasing them from the same retailer, even if doing so means it takes longer to deliver, the study suggests. Online retailers, on the other hand, can shrink their emissions by finding cleaner delivery vehicles along what’s called the “last mile” — the last stretch from a warehouse to someone’s front door.

Taking these steps into consideration is only going to become more important as more shoppers turn to the internet to buy everyday items like groceries, toiletries, and cleaning supplies, which are referred to as “fast-moving consumer goods” in the study. People buy more of these products every week compared to other items that are frequently bought online, like clothes or electronics.

“The overall impacts from [fast-moving consumer goods] shopping is much larger compared to shopping for other products,” Sadegh Shahmohammadi, an author and researcher with the Radboud University in the Netherlands, said to The Verge in an email. He points out that the number of people buying these household necessities online is growing rapidly. That’s worrying because his study finds that online-only shopping is also the most greenhouse gas-intensive option.

In-store purchases had a smaller greenhouse gas footprint than online purchases shipped from faraway distribution centers in 81 percent of the study’s simulation runs. Purchases shipped from afar had median total greenhouse gas emissions that were twice as high as in-store purchases and about two to five times higher than items bought online but delivered from a local store.

The study published today in the journal Environmental Science & Technology was completed by researchers with Unilever and from the Radboud University Nijmegen; they received funding from the European Union. They modeled the greenhouse gas emissions from fast-moving consumer goods (using Unilever products as examples for calculating the weight and volume of goods bought as well as data from Unilever on energy usage from warehouses and on whether their products are typically transported via ship, train, or truck). They took into account the greenhouse gas emissions generated at every step of the shipping process, from transport from a factory to a warehouse and / or store, storing the item, and sending it out to a customer. They also considered packaging for deliveries from warehouses only, contending that packaging from brick-and-mortar stores was negligible.

Research from about a decade ago found that buying stuff online can result in less planet-heating pollution than driving to a store yourself. Shoppers stayed at home instead of driving gas-guzzling cars to and from the mall. But a lot has changed since then. Delivery vans make more trips in order to satisfy consumers’ expectations for fast deliveries. Returns add on more trips.

“The world has changed over the past few years. And therefore, it’s quite right that people are coming along and saying we have to reassess what the net environmental effect is of online retailing,” says Alan McKinnon, a professor at the Kuehne Logistics University in Hamburg, Germany. He was not involved in the study, but his research was cited in the paper.

McKinnon says he welcomes new studies like this that call into question whether there are still environmental gains to shopping online, and he points to some of the study’s limitations. One limitation is that the study calculates emissions from courier services like UPS. Amazon is increasingly shipping products itself and is purchasing electric vehicles to cut down its emissions. Another major limitation: people still don’t mirror their supermarket purchases online. The study authors explain that people still buy a lot of food in grocery stores, while items like baby care and personal care products are more popular online.

“At the end of the day, it’s still a complex subject,” McKinnon cautions. “It’s hard to make a consistent comparison.”