Does Ebay Shipping Hurt the Environment?

A recent New York Times story explores how eBay is trying to market an environmental appeal for buying used goods. The story ends with some economic discussion:

EBay hired Cooler, a company that calculates carbon footprints, to determine how much carbon shoppers save by buying something used instead of new. They say that the leather handbag, for example, saves as much energy as a flight from London to Paris.

Cooler calculated the total cost of creating a new item, including materials and manufacturing, and factored in the cost of packaging and shipping eBay items via fuel-guzzling planes or cars, Ms. Skoczlas Cole said.

I doubt that the shipping of eBay items hurts the environment much, on the margin.

New items also have to be shipped: from the manufacturer to the retailer and from the retailer to the customer's home. It's unclear that shipping used items requires more fuel, so a shift from new goods to eBay goods isn't necessarily bad for the environment.

Additionally, shipping is dominated by fixed costs--a certain number of trucks and delivery routes exist regardless of whether you send your item, so mailing one more package probably isn't going to burn more gas.