San Francisco environmental officials are hoping to cut down on grocery bag pollution. This week they're expected to ask authorities to consider a tax on paper and plastic grocery bags. You'd have to pay 17 cents per bag. The move is fiercely opposed by grocers. They say that many people already reuse their bags — that's recycling, isn't it? But city officials say that discarded bags drift in the wind, and decorate too many of the city's trees.