I would be surprised if the production of a cardboard box is carbon-negative. edit: I had to look. Some article suggesting cardboard is worse than plastic: https://www.theguardian.com/environment/2010/mar/31/plastics-cardboard A site that says the CO2 emissions for cardboard generation is: 3.3 kg per kg: http://www.greenrationbook.org.uk/resources/footprints-cardboard/ Europeans really getting into the details: http://www.cepi.org/system/files/public/documents/publications/environment/2017/NEWcarbon%20footprint-final_1.pdf I don't think cardboard counts as sequestration.
Just saw this post because of a link, so sorry to revive a dead thread. But I've been thinking a lot recently about how whoever comes up with a logistically workable reusable shipping box system is going to make a fuckload of money once carbon cap and trade is a thing. Basically they'd be manufacturing CO2 credits. Tesla sells their ZeV credits to FCA and already makes a lot of money off it. It's going to be a growth business, but I thin it will take a shitload of capital up front, so probably only Amazon can pull it off.