What is the difference between negative externalities and demerit goods?

What's the difference in environmental cost (carbon footprint) between online ordering and traditional retail for fast moving consumer goods?

• Services like make the ordering of fast moving consumer goods (FMCGs: http://en.wikipedia.org/wiki/Fast_moving_consumer_goods) such as groceries, toiletries, etc incredibly convenient. Items are shipped within two days for free, and the service even allows one to setup automatic scheduling for replacement purchases. But is this bad for the environment? If I wanted shampoo or mouthwash, would I be doing more or less harm to the environment if I drove down to my local or and bought it there instead of ordering through Amazon? On the one hand, if enough people switch to the online ordering and delivery of FMCGs, the supply chain would be simplified so that less trucks serve more people, so the carbon footprint is reduced in that respect. On the other hand, don't people go out and drive around to work and other places anyway? Wouldn't driving to a local pharmacy or supermarket to acquire these goods be marginal in the final carbon footprint calculation? Another consideration is packaging. Major warehouses and distribution centers receive these goods from suppliers on large pellets, then each items or small group of items must be broken down and repackaged into a smaller box for delivery to a single address. Doesn't that add to the carbon footprint as well (environmental cost of producing boxes, delivering boxes, etc)? At traditional sources of FMCG acquisition, the items are also delivered on pellets but not repackaged like in the online model. So what's the difference, environmentally?

• Answer:

  Hey, here is a study on products carbon footprint with focus on the final stage of the supply chain, between the retailer and the consumer. This stage of the supply chain is also commonly called the "last mile". In brief, they showed that online shopping using van or truck load delivery will be 40 times more carbon efficient compared a single car trip with the sole objective to buy one or two items from a store. They also considered the other scenarios you have mentioned. http://www.greenlogistics.org/SiteResources/ee164c78-74d3-412f-bc2a-024ae2f7fc7e_FINAL%20REPORT%20Online-Conventional%20Comparison%20(Last%20Mile).pdf