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Synthetic fibers and other plastics are made from oil--a fact that seventy-two percent of Americans in 2007 didn't know, according to an online survey--and our world, increasingly, is made of plastic. Preferring items made from natural materials is a strategy often recommended as environmentally sensitive, but forsaking pantyhose, Under Armour, eyeglasses, cell phones, personal computers, running shoes, snowboards, sleeping bags, and all our other oil-based possessions poses the same unhappy dilemma that promoting ethanol does: it diverts agricultural capacity and resources (all those new rubber plantations and flood-irrigated cotton fields!) away from the production of food. The world is suffering food and water shortages already; should vegans reconsider fur coats?

Near the southwestern end of Lake Mead, 20 miles from the Las Vegas Strip, an earthen causeway runs between the shore and Pyramid Island. Two cantilevered piers extend like wings from the causeway's sides. There used to be a "No Fishing" sign at the end of one of the piers, but it served no purpose beyond stating the obvious: the lake's volume has shrunk by nearly 60 percent since 1998, and the piers overhang dry land. The lake's rapid decline is mainly the result of an ongoing drought in the Southwest and of reduced snowfall throughout the watershed of the Colorado River, which feeds it. A section of the lake to the south of the causeway used to be reserved for scuba diving; today, you can explore it in hiking boots.

Water pumped from the Colorado is apportioned according to a 1922 agreement, which annually allocates 15 million acre-feet among seven states. Most of that water goes to agriculture, much of it to environmentally questionable activities such as growing heavily subsidized cotton in Arizona. Cellulose, pea starch, and high-fructose corn syrup, among other unlikely-sounding substances, may turn out to be useful as natural sources of polymers that can be turned into commercially viable non-petroleum-based fibers and other plastics. But these possibilities raise the same discouraging question that all plant-based petroleum replacements do: we can't eat our crops and wear them, too, especially if we are also depending on them to fuel our cars.

David Owen, Green Metropolis, environment, sustainability, urban living, green living