It can be hard to resist the pull of online shopping and the satisfaction of getting an item in less than two days without even leaving the house. What most people don’t consider is the climate impact of that convenience. When it comes to shipping products, the “last-mile” of delivery—the final step before a package reaches your front door—produces the most emissions as drivers make multiple stops, linger in traffic, and often take inefficient routes to meet tight delivery windows. One 2022 study found that up to 50% of a delivery’s total carbon emissions are from the "last mile". The demand for ultra-fast shipping has heightened the issue. “If you have expedited shipping, then you are not actually able to consolidate [packages,]” says Dr. Sreedevi Rajagopalan, director of the MIT Sustainable Supply Chain Lab. “As a result, you end up delivering less goods in a short period. You also end up visiting the same route, maybe multiple times the same day or consecutive days. So that actually results in very high emissions.”Read more: The Health and Climate Benefits of Slow LivingAn increasing number of delivery companies are moving to make their last-mile delivery more sustainable—including electrifying their fleets of delivery vans. Retail giant Amazon has committed to getting at least 100,000 electric delivery vehicles on the road by 2030, while FedEx has pledged to convert its entire delivery fleet to zero-emission electric vehicles by 2040. Rajagopalan says that other changes—like encouraging customers to consolidate their items into one package or pick a slower shipping option can also help companies reduce the high emissions associated with last-mile deliveries.What is the climate impact of fast shipping?Online shopping isn’t necessarily less sustainable than in-person shopping. One 2021 study found that shopping in person results in anywhere from 1.5 to 2.9 times more greenhouse gas emissions than online shopping. However, a number of factors play into the sustainability of either option. “If you are going to use your own car or if you go to the store more often, then it is going to lead to an increase in emissions [compared to] using public transport and making purchases once in a week instead of going every day,” Rajagopalan says. After Amazon and Walmart rolled out same-day delivery options for customers in 2015 and 2017, researchers created a model that found that the practice was both more expensive and more carbon intensive—increasing both total CO2 emissions and costs up to 15% and 68%, respectively.Read more: You Can Now Calculate Your Grocery List's Carbon FootprintOne thing’s for certain: online shoppers return three times as much merchandise as brick-and-mortar shoppers, which drives up emissions and creates further package waste. (Not to mention, 5.8 billion pounds of returned merchandise ends up in landfill each year, according to Optoro, a logistics company that specializes in returned merchandise.) Consider your purchases before you make them, and if you’re uncertain, see if you can test out or try on a product in a store near you before you buy it. How can I adopt more climate-friendly online shopping habits?How you order online can make a difference. Rather than placing small orders throughout the week or month, take time to consider your purchases and make them all at once. Some retailers give customers the option to bundle items together, which might take longer to ship, but uses less packaging and reduces the number of delivery trips. If the option is available, avoid same or next day delivery. Delaying a delivery by three to four days can reduce emissions from anywhere from 40% to 56%, Rajagopalan says. As Rajagopalan puts it: “It's important for us as consumers to sit back and think, ‘Do I really need this product tomorrow?’”