Online shopping generates additional emissions from two major sources: additional packaging and shipping. Shipping is not a large contributor mostly because so many packages are shipped at once that the miles travelled per package is usually less than a mile. Furthermore, products that you buy in a store were still shipped - you're just becoming the delivery person by going to the store but the problem is that when it's delivered to your house the delivery person is making 100-300 stops and you're probably only making several.
The packaging for shipping is where the problem comes in. The largest additional emissions that online shopping generates comes from the box its shipped in. Each package emits about the same as a gallon of gas, mostly due to the box - so if you can go to the store for less than a gallon of gas, it's better than ordering online.
Delivery Speed and Distance
Delivery speed matters, but probably not how you might think at first. In shipping it takes about a day for an item to get from the last warehouse/depot to a small final destination like a house or small business. And so long as the item isn't flown, it can travel about 600 miles in a day by truck when including routing logistics time.
Let's take two-day shipping as an example: for that item to get to you without flying it has to come from a warehouse within 600 miles (based on UPS ground cross country/regional shipping times). One day to get it to your city and another to get it to your exact location. Same/next-day shipping? That item has to come from within your metro area. Amazon isn't likely overnighting items to you to achieve same-day shipping because it'd cost too much - so they're probably stocking that item close enough to you that they can put it right on the final delivery van. Meaning that same-day shipping from a large retailer can be the most emissions efficient option!
How small retailers compete
Smaller retailers don't have enough volume to justify their own logistics networks but that is where commercial logistics companies like FedEx and UPS come in. These companies work as external shipping networks working to combine the needs of many retailers so that they can get efficient delivery costs (and therefore emissions). But it comes at the expense of speed as Amazon has so thoroughly demonstrated.
Is a large or small retailer better than the other from an emissions perspective? The shipping itself is probably fairly similar, especially if there isn't a plane involved. But larger companies with huge internal logistics networks have a couple of advantages:
- they can make sure that a higher percentage of orders don't need flights to be delivered quickly
- if you order multiple things and they stocked those items in the same warehouse, they can use fewer boxes which is the most important factor in the emissions of an item
- they can route items directly from a port to the distributed warehouse instead of through a centralized warehouse (say Los Angeles Port -> San Francisco distribution center instead of Los Angeles Port -> Colorado Distribution Center -> San Francisco distribution center). This means that the items are likely travelling a shorter distance overall which is lowering emissions but this is likely an extremely small effect since so many packages are being transported to warehouses.
Local vs. Foreign
Often locally made is touted as better environmentally but that isn't necessarily true because it is close by. Transportation doesn't dominate the total environmental impact of a good, the energy to produce it does. So it more matters how the electricity is generated in the region that it is made more than how far it is transported (this becomes wildly untrue if the item must be transported quickly - fruits are a great example of this but we're also getting better at preserving fruit during transport allowing it to be shipped by more fuel efficient means).
Secondly, unless all the input materials for that good are made locally as well, the components of the good are still shipped, nullifying the locally made benefit. Ultimately, it is more efficient from an emissions perspective to make goods in locations powered by clean energy and to eliminate waste than it is to make things locally.
The future of delivery
Where is all this headed? Overall, delivery would be a lower emissions solution than in person shopping if the packaging problem could be solved. It also has interesting potential for packaging since the display of the item online can be different than the actual packaging allowing more flexibility in the packaging design.
Some large retailers like Amazon are well aware of their carbon footprint and are working hard to reduce so you can be sure it and they're likely focused on packaging to start. Large companies are also adopting electric delivery vans and semi-trucks. In fact vans and trucks are the place it makes sense to electrify transport first because they travel so many miles and it's easier to justify the cost. In the long run, more dedicated delivery systems like drone delivery could eliminate the need for a disposable box all together. While drones will likely consuming more energy per package than a truck, they can help replace fossil fuel delivery vehicles while we work to replace the world's supply of delivery vans.