The other day I bought a watermelon at a small supermarket in Cambridge. The market used to give away super thin plastic bags so I was about to ask for the melon to be double-bagged. The clerk then pulled out a bag that was at least as thick as a “contractor” garbage bag for disposing of 2×4 fragments. Probably 25-50X as much plastic went into the new-style bag as had gone into the old one. What changed? The city has made it illegal for merchants to give away bags. They have to charge 10 cents for each bag by law. Apparently this grocery store doesn’t want to be seen as ripping consumers off so they have laid in a stock of the world’s thickest and strongest plastic bags. Unless at least 95 percent of customers actually bring their own bags to the store, then, the effect of the law will be to increase the use of plastic.