The relationship between economics and environmentalism is something politicians and activists seldom get right, though it's interesting to note that the communist government of China seems clearer on the concept than the government of San Francisco -- or the state of California. Fortunately, when it comes to phasing out plastic shopping bags, Los Angeles County is looking west rather than north for role models.
Those plastic bags handed out by grocery stores, takeout restaurants and other retailers are an environmental catastrophe. They're petroleum-based nuisances that take generations to break down, clogging our rivers and storm drains, polluting our parks and threatening marine life. San Francisco's response last year was to ban them outright. In the City by the Bay, the question isn't paper or plastic but paper or potato; stores can no longer offer plastic bags, but they can offer biodegradable alternatives made from potato-starch or cornstarch.
The trouble with this approach is that it amounts to a hidden tax. Plastic bags cost stores about a penny each, while biodegradable alternatives cost from 4 to 8 cents. Those extra costs are being passed on to consumers in the form of higher prices for food and other goods. The starch bags also don't entirely solve the pollution problem because they may never break down in landfills, which are sealed to prevent water seepage and thus "mummify" everything dumped in them, biodegradable or not.